Ramsey FX-146 User guide

2 METER AMATEUR PLL
SYNTHESIZED FM
TRANSCEIVER 140 - 180MHz

Ramsey Electronics Model No. FX-146

• Synthesized - no crystals to buy !

• Perky 5 watt RF output

• Dual conversion sensitive receiver with crystal and ceramic IF filters

• PACKET ready ! Dedicated packet interface connector on back!

• 12 Channels, expandable to as many as you want - programmed with

diodes !

• Easy 4 evening assembly - need only a voltmeter and another rig for

testing

• Fantastic manual teaches as you build, rig is assembled in bite-sized

sections that are tested as you build - your kit will work first time !

• Rig operates over 20 MHz of band, great for snooping out of band !

• Be proud to say...The rig here is a home-brew!

Published in Three Sections:

• FX-series General Reference Information

• Kit Assembly Phase I: Circuit Stages A through F

• Kit Assembly Phase II: Circuit Stages G through TX

Plus:

• Fold-out Schematic Diagram

• Fold-out Multi-color Parts Layout

FX-146 • 1

A DEDICATION

The Ramsey FX-series FM Transceiver Kits are writing a truly NEW chapter
in the annals of the ham radio story. Growing numbers of today's radio
amateurs ARE willing to build, understand, adjust and maintain modern VHF
gear capable of digital frequency programming and data communication as
well as FM voice. How do we know? We know it because, during 1991,
thousands of hams worldwide built and are using our pioneering FT R-146 for
two meters. The FX Transceiver design was developed in immediate
response to those builders' suggestions, wish lists and inquiries. T his
publication is dedicated with deep thanks to all those FTR-146 builders!

FX-146 VHF FM Transceiver Reference and Kit Assembly Manual
Ramsey Publication No. M146FX
First Printing: December, 1991
Copyright 1991,1994 by Ramsey Electronics, Inc. All Rights Reserved.
Revision number 2.0
Published by Ramsey Electronics, Inc. Printed in the United States of

America

RAMSEY ELECTRONICS, INC.

Amateur Radio and Hobby Kits Dept.

793 Canning Parkway Victor, New York 14564

[phone] Fax: [phone]

FX 146 • 2

TABLE OF CONTENTS:

The Ramsey FX-146 Tranceiver Manual is organized into three sections:
General Reference Information, Kit Assembly Phase 1, and Kit Assembly
Phase 2.

FX-146 GENERAL REFERENCE INFORMATION

Notice Regarding FX-146 Frequency Coverage ................................4

FX-146 Technical Specifications........................................................5

Introduction to Transceiver Kit Assembly...........................................6

A Message to Ham Radio Beginners .................................................8

DC Power Supply Considerations......................................................9

Enclosure and Hardware Considerations.........................................10

Ramsey CFX Transceiver Enclosure Kit ..........................................12

Guide to PC-board I/O Connections.................................................14

Microphone & Speaker Information..................................................16

A Few Antenna Considerations........................................................16

VHF Packet Data Operation.............................................................17

FX-series Transceiver Block Diagram..............................................18

FX-146 Circuit Overview...................................................................19

Quick-Reference Programming Guide .............................................28

FX-146 Programming Worksheet.....................................................30

Using Computer BASIC as a Programming Aid...............................32

How to Activate an Auxiliary (non-Standard) Offset.........................35

Programming "Minus" Offsets...........................................................36

FX-146 Programming Summary.......................................................38

Basics of Externally-Controlled Frequency Switching......................38

FX-series GLOSSARY of Terms ......................................................40

Troubleshooting Guide .....................................................................46

Note on Replacement Parts..............................................................48

FX-146 Master Component Index ....................................................49

RAMSEY ELECTRONICS FX Kit Warranty Terms..........................62

KIT ASSEMBLY: PHASE 1

Assembly and Explanation of Circuit Stages A through F
(including Kit Parts List, kit-building tips and preliminary receiver & VCO

test)............................................................................................63 - 98

KIT ASSEMBLY: PHASE 2

Assembly and Explanation of Circuit Stages G through TX (includes all
Frequency Programming directions plus alignment and transmitter tuneup.)

................................................................................................ 99 - 137

Optional Helical Filter Installation...................................................138

Technicians Notes..........................................................................139

FX-146 • 3

IMPORTANT NOTICE

The Ramsey FX-146 VHF FM Transceiver is capable of
TRANSMITTING as well as receiving on any frequency in the
range of 140 to 180 MHz, making it suitable for a wide range of
VHF communications requirements. Operation of the Transmit
function of this equipment requires an appropriate license
issued by the Federal Communications Commission (FCC) for
the class of operation intended. The FCC issued TECHNICIAN
CLASS license or higher is required for operation in the
Amateur 2 METER band (144 to 148 MHz). Proper licensing is
required for MARS or CAP operations. Amateur licensees are
required by the FCC to maintain strict control over their
equipment to prevent unlicensed operation either in the
amateur band or outside it. FCC regulations ENFORCE severe
penalties for unlicensed operation of radio transmitting
equipment and for interference with other communications
services, whether malicious or accidental. Ramsey Electronics,
Inc. sells the FX-146 transceiver solely for correctly-licensed
operation. It is the sole responsibility of builders and operators
of this RF electronics device, capable of emissions controlled
by FCC Rules, to understand and comply with those rules.

FX 146 • 4

SPECIFICATIONS FOR THE RAMSEY FX-146
General:

Frequency Range: Any 20 MHz segment between 140 and 180

MHz

Tuning: Diode-programmable PLL synthesis 12 front

panel selected frequency pairs, easily
expandable by switches, microprocessors,

computers, etc.
Programming: 5 KHz steps with programmable offsets
Transmit Offset: Programmable: Simplex, +1.2, -1.2, Aux
Mode: NBFM
Packet (Data) Operation: All rates incl. 9600 baud . 5-pin DIN jack

(TXD, RXD, PTT, +12VDC, GND)
Packet RX Audio: Speaker, discriminator or true FSK
Power Requirement: 13.6V DC +/-10% (Negative ground)
Power Consumption: 1.0 A Transmit (for 5 watts RF output) 200

ma. (Receive, no signal)
Antenna Impedance: 50 ohms
Microphone Impedance: 600 ohms or high impedance
T-R switching: PIN diodes
PTT circuit: Solid State (for standard ICOM-type

speaker/mic connection)
Semiconductors: 10 IC's, 16 transistors, 24 diodes (plus

programming diodes)
Transmitter:
Final Power Output: 4-6 watts RF
Final Output Stage: MRF237 or equivalent
Modulation: True direct FM
Max frequency deviation: +/- 25 KHz, +/- 5KHz NBFM
Modulation distortion: Less than 5%
Receiver:
Circuitry: Double-conversion superhet

First IF: 21.4 MHz
Second IF: 455 KHz
Sensitivity: 12 db. SINAD less than 0.35 uv
Selectivity: 7 KHz (-6db.), 15 KHz (-60db.)
Squelch sensitivity: Less than 0.25 uv
Audio output: More than 2.0 watts
Circuit access points: COR, PL tone input, FSK demod. +12V,

+8V, +5V, PLL programming.

FX-146 • 5

INTRODUCTION
to FX-series VHF Transceiver Kit Assembly

For the 1990's, Ramsey Electronics has adopted a "Learn As You Build"
philosophy for ALL our electronics kits. We feel that licensed ham operators
should know about the equipment they use, and also should have the desire
to understand how their gear works. Additionally, it has been our corporate
response to all those urgings by public officials that both students and their
parents need to become sharper in science and math. This "Learn as You
Build" approach to electronics hobby kits is now evident in all Ramsey
Electronics build-it-yourself kits from our under-$5 student kits up to this
synthesized VHF transceiver suitable for ham radio and public service
applications alike.

We think that "learning (and UNDERSTANDING) as we build" is especially
essential in a more sophisticated project such as the Ramsey FX-series VHF
transceivers. In fact, we are so convinced of this basic need that this kit
instruction manual departs from the traditional scheme of separating
assembly directions from a "theory of operation."

The FX-series of Ramsey VHF/UHF Transceivers puts today's FM 2-way
radio technology back in YOUR hands at a budget price. Our idea of
"budget" looks far beyond the modest purchase price to our goal that you
can maintain your FX- unit in good operating readiness with no need for
expensive shop service. On the other hand, we also have made the
transceiver design as abuse-proof and rugged as possible. "Alignment,"
traditionally an intimidating many steps process is very easy, quick and fool­proof in this circuit design.

Instead of separate stage-by-stage assembly directions plus separate theory
information, these FX- instruction booklets highlight your transceiver's
operational theory, often a single component at a time, with actual
construction steps provided as follow-up after each explanation. The
assembly sequences are easy to find in the following pages. You indeed
have the freedom to solder first and read all about it later. We hope, though,
that you'll take it easy, learning as you build, and then enjoy the reliability of
your Ramsey FX Transceiver for a long time to come.

The "style" of our kit-building directions presumes that you are peeking at
our multi-color parts layout sheet while seeing that the very same parts
outlines are imprinted on the component side of your FX- PC-board. Our
smaller kits do not justify any need for on-board imprinting (silkscreening).
Therefore, such kits provide more detailed published explanations for
identifying correct locations for inserting and soldering parts.

You'll install EVERY FX- part perfectly by using our simple step-by-step kit
building process. And you'll know the WHY of most assembly steps, if not all
of them. Before you start, THINK about what you'll create from those bags of

FX 146 • 6

parts as a finished product! For a minimal investment of your time as well as
your well-earned money, you will have a VHF FM voice-data transceiver that
you will truly own. Real "owning" ultimately means knowing how to maintain
and understand something that we have, in contrast to merely possessing a
thing because you spent the bucks to do so. You'll have the flexibility of 12
channels chosen by YOU with the easy ability to change or expand. You'll
have both FM voice and high-speed data capability. When you're ready, you
can experiment with many different enhancements, concentrating on those
truly useful to you. If there's ever a problem, you won't think twice about
digging in and fixing it. Whenever you decide you could use still another
VHF/UHF FM/data transceiver at a budget price, you'll know with confidence
that an FX-series kit is the right way to go.

What's faster: turning your FX- Transceiver to any one of 12 possible
channels programmed by you, or trying to remember again exactly how to
use the memory pre-sets of your HT, or your HF rig, or the VCR, or the
microwave?

Let's learn about and build up a FX- VHF FM Transceiver!

FX-146 • 7

A MESSAGE TO HAM RADIO BEGINNERS:

If you have just earned your Novice or Technician license, or are studying for
either of them right now, we'd like to say a special Thank You for choosing
this Ramsey VHF/UHF transceiver as part of your ham radio beginnings. We
have tried to make this instruction manual as clear as possible. However,
there are some VHF radio "basics" covered by the FCC question pools for all
ham license study guides that we must presume that you have studied and
understood.

Here is a simple guide to selected Technician Class questions to help with
any review you wish to make before building:

FCC Subelement 3AA (Selected Rules): 4.2 11-1.1 12.5 15.2
FCC Subelement 3AB (Operating Procedures): 2-1.1 2-1.2 2-1.3 2-1.4

2-1.5 2-2.1 2-2.2 2-3.1 3.2 6-3.1

FCC Subelement 3AC (Propagation): It's up to you to understand the

characteristic differences among HF
(shortwave), VHF and UHF
communications.

FCC Subelement 3AD (Amateur Radio Practice): All of this is fundamental

know-how for hams. In working on this
project, be especially familiar with: 1-1.1 1-

1.2 1-1.3 7.1 9.1 through 9.5 (dummy
loads)

FCC Subelement 3AE (Electrical Principles) 3AF (Circuit Components)

Please know ALL of this.

FCC Subelement 3AG (Practical Circuits): 4.21
FCC Subelement 3AH (Signals and Emissions): 1.1 2-1.1 2-4.1 2-6.2

2-7.1 4.1 6-1.2 7-1.1 7-2.1 7-2.2

FCC Subelement 3AI (Antennas and Transmission Lines): You will want

to know all of this, if you don't want to take
all your savings from building your own
transceiver and spend it on a commercially­built antenna. Very good VHF antennas are
easy and inexpensive to build yourself!

FX 146 • 8

DC POWER SUPPLY CONSIDERATIONS :

Your Ramsey FM Transceiver is designed to operate from any stable DC
voltage source in the 12 to 15 volt range, from typical car, boat or plane 12V
systems to a wide variety of battery packs or AC-powered DC sources. In a
pinch, you can get on the air for quite a while with 8 to 10 ordinary "D" cells!
Our lab tests show only a .93 amp current draw for 5 watts of RF output. We
have just a few points of advice and caution:

1. Your DC supply should be able to provide a minimum of 1.0 amperes in

continuous service.

2. Any battery setup capable of supplying 12-15VDC will serve quite well.

3. Use of wall plug power supplies is NOT recommended. Obviously,

12VAC output is not suitable. Most DC output units do not have
adequate voltage regulation.

4. Turn your transceiver OFF before re-starting the vehicle in which it has

been installed.

5. Replace F1 only with a 1 amp fuse.

6. If you power your transceiver from the +12V accessory voltage available

from other equipment, be sure that source is rated for the 1 amp
required.

7. Your transceiver circuit includes noise suppression at the DC input and

additional filtering at the VCO, primarily to prevent ignition/alternator
noise from being introduced into the FM modulation. If you hear ignition
noise in the receiver, the vehicle has a serious general problem. Check
your transmitted signal on another receiver before mobile operation.
Radio Shack sells a variety of noise-suppression capacitors and
chokes. The ultimate solution, which has been tested, is to run the
transceiver from a smaller accessory battery.

If you plan to build a power supply for fixed-station use, there are numerous
construction articles in ham and electronics hobby publications. A
convenient new book featuring easy-to-find components and clear
explanations is Building Power Supplies (Radio Shack 276-5025.)

FX-146 • 9

ENCLOSURE & HARDWARE CONSIDERATIONS:

The companion CFX case and knob kit is sold as a separate option ONLY
as an accommodation to those radio hams who have their own ideas or
resources for the "finishing touches."

However, a proper case for your FX-series is much more than a "finishing
touch," since the controls and jacks are panel mounted and proper RF
shielding is required.

The CFX case measures 9-3/4"L X 6"W X 1.5"H. 9" x 6" dimensions are
minimum for accommodating the PC board. The height may vary if you wish
to include an internal speaker, accessory PC boards, additional front panel
controls or indicators, etc. If you are new at all this and do not already own a
suitable enclosure plus that collection of hardware and knobs that every ham
seems to accumulate, here is what you need to know if you are hesitant to
purchase the CFX case kit:

A. "Blank" electronics enclosures have become among the most

expensive hardware in the industry, especially if you are buying just one
unit. This is because they are sold mainly to engineers and designers
for prototyping. A blank metal enclosure even slightly comparable to the
CFX case kit will run $30 to $80 or more. Even a plain aluminum
chassis box/cover will be around $15.00.

B. If you think there's any chance you someday may wish to sell or trade

your transceiver, you should be aware that units mounted in odd boxes
may have even less value than the bare circuit board with

documentation alone.
C. Many distri butors have a minimum mail order of $25.00.
D. Your best chance for finding an inexpensive alternative case is to have

access to a lot of ham friends who tend to "collect stuff," or to browse

the catalogs or showrooms of electronic surplus dealers. You just might

find a gorgeous new box originally intended for somebody's ingenious

Ultra Modem, external disk drive or other dream gadget from two years

ago.
Are we trying to discourage you? No, not really! We know you can see that

there are good reasons to consider calling Ramsey Electronics and getting
your CFX case on its way while you work on the PC-board and PLL
Programming. However, we do not want you to feel "stuck" with our
recommended CFX enclosure, so we have worked up a detailed shopping
list for getting what you will need to make as attractive a finished unit as
possible with a single trip to the neighborhood Radio Shack store.

FX 146 • 10

Quantity RS Part No. Description 1992 Price ($)
1 270-272/74 Deluxe Project Enclosure 8.79 or 10.79

1 set 274-section Pkg. of 3 or 4 knobs 2.00-3.00

1 set 270-201 Rub-on project labels 2.99
2 sets 276-195 PC-board standoffs/ 2.38

This $16 to $18 (plus tax) in basic hardware also presumes availability of all
needed drill bits and/or a reamer or punches of sufficient size to make the
needed access holes for the rear panel jacks. You'll also want to figure on
spray paint as well as a clear finish to protect the panel labels. Tools and
supplies, if not on hand, could cost much more than the CFX enclosure kit
itself.

In addition, this style of case will have to be utilized upside-down and also
length wise rather than as designed. This means that the top (black)
becomes the foundation for mounting the PC board with the standoffs as
well as securing the SO-239 antenna connector assembly. You may wish to
repaint the white bottom which now becomes the top. And, to use the project
labels (black lettering), you'll probably wish to repaint both pieces.

This adaptation of standard Radio Shack hardware is adequate for indoor or
occasional use but not recommended for mobile operation. We are happy to
provide this suggested alternative to the rugged case, knob and hardware kit
custom designed for the FX-series transceivers. The choice is yours!

FX-146 • 11

THE RAMSEY CFX TRANSCEIVER ENCLOSURE KIT:

The CFX Kit is very obviously a fair value and solid investment for the long
term performance and worth of your transceiver. As we have mentioned, we
make it "optional" ONLY because some of our ham customers have
specialized applications requiring only the basic PC board kit. We try
whenever we can to accommodate that important do-it-yourself spirit of ham
radio.

ENCLOSURE KIT PARTS LIST

Please check the boxes after the components have been identified, and it is
also handy at this time to “sort” the like components into groups or bins (an
egg carton does nicely) to avoid using the wrong component during
assembly.

 1 Steel bottom shell with 5 threaded PC board standoff posts
 1 Steel top shell
 1 Front control panel
 1 Rear panel with access holes to PC mounted jacks
 2 Steel side rails
 5 PC board standoff spacers
 5 #4 nuts to secure PC board on standoffs
 8 #4 screws to mount front and rear panels
 8 #6 screws for securing top and bottom to side rails
 1 large knob for Channel Selection Switch
 2 smaller knobs for Volume and Squelch controls
 4 self-adhesive rubber feet

CFX CASE ASSEMBLY PROCEDURE:

The purpose of these hardware parts is largely self-evident. We offer the
following suggestions for your convenience and to minimize wear and tear
on your factory-fresh CFX enclosure.

 1. Since the bottom shell might be used for several "test fittings" during

transceiver assembly, install the rubber feet right away to protect its

finish.
 2. Obviously, the PC board cannot be secured permanently to the

bottom section until after installation of L9, R32 and L10 AFTER

Alignment and before Transmitter tuneup.
 3. Install the strain-relief grommet supplied with the transceiver kit in its

rear panel hole. Pass the black ground wire through this grommet. The

red, fused wire will have to be unsoldered from S1 and then carefully

FX 146 • 12

resoldered after passing through the grommet. Snap in the locking
section of the relief grommet only AFTER both the red and black wires
are in place.

 4. Remove the two screws from the SO-239 antenna connector, gently

bend the lugs as needed to match the rear panel holes, then secure the
jack and lugs to the rear panel.

 5. Since the top shell will not be needed until you're ready to go on the

air, keep it wrapped in protective material until you're really ready to use
it.

 6. The side rails may be installed to the bottom section at any time. To

prevent loss of the screws for the top, keep them loosely threaded in the
side rails.

 7. There is no point in securing the front panel controls and jacks to the

panel permanently until AFTER wiring the Channel Selection switch.
Note the locking hole for the switch in the front panel which mates the
tab on the front of the switch.

 8. Use care and a well chosen pair of pliers to secure the microphone

and speaker jacks to the front panel, so as not to scratch the panel.

 9. Bend the leads of the TX LED so that their tension presses the front

of the bulb against its front panel hole.

 10. Whenever you find it necessary to remove the top shell, "store" the

screws back into their holes in the side rails.

 11. If you decide to install a ribbon cable in the diode matrix for external

programming control, route the cable (folded at a right angle) on the
synthesizer and receiver side of the board so that it exits the case
between the rear panel and top cover, right above the DC power cord.
Do NOT route any such cable across the VCO and transmitter side.

 12. After the PC board is secured to the case bottom and front/rear

panels, it is a good idea to neaten up the wires to the controls and
jacks, bundling them at two or three points with tie wraps or cord.

FX-146 • 13

GUIDE TO PC BOARD I/O CONNECTIONS:

In addition to primary interconnections required for jacks and controls, etc.,
your FX-series Transceiver PC board provides additional access to
operating voltages and circuit features to make later customizing as neat
and easy as possible. All these points are plainly marked on the board itself
and highlighted on the facing page, with a few other components for

FX 146 • 14

1. PRIMARY CONNECTIONS:

PWR (near L20): +12-15 volts DC from S1.
GROUND: - DC from battery or power supply.
SPEAKER: both connections near C37
MIKE: both connections (IN & GND) near notched end of U1.
SQUELCH: two connections marked CW and W near C18
VOLUME: three connections marked IN, OUT, GND.
ANTENNA: Center of SO-239 connected at "RF OUT" near C71.
CHANNEL SWITCH: Row of holes numbered 1 through 12. The switch

wiper (moving contact) is wired to +5V near "1."
EXT AUDIO: must be jumpered per options to enable pin 4 of J1.

2. TEST POINTS:

+12V, +8V, +5V, +8R, +8T permit checking for presence of those voltages.
+8R = Receive mode. +8T = Transmit.

TP1: For checking of VCO control voltage during alignment.
TP2: For checking VCO frequency with counter.
TP3: For checking U3 prescaler output with counter.
R103: +7VDC at top lead shows locked PLL. 0 volts = problem.

3. OPTIONS:

+12V, GND, +8V, +5V, +8T, +8R: provide supply voltage for accessories or
modifications designed by you. +5V is available both near L1 and near
C102. +8T and, +8R are near Q13, Q14.

Jumper Options for Packet Operation: SPKR to EXT AUDIO: Speaker level
audio for packet (J1). DISC to EXT AUDIO: FM discriminator output for
packet.

COR: "Carrier Operated Relay" output from U1.
PL: Input point for audio tones (DTMF, CTCSS, etc.)
Binary Programming Holes: The row of holes alongside the Binary

Programming labels permits installation of ribbon cable for external
programming devices designed by the innovative amateur radio community.
switches or interfaces, or a row of internal DIP switches.

FX-146 • 15

MICROPHONE & SPEAKER INFORMATION

The FX transceivers with the hardware supplied are designed to accept
standard ICOM or ICOM-compatible speaker-mikes such as MFJ-284. The
most conveniently available such unit is Radio Shack No.19-310.

Be aware that the receiver audio amplifier is capable of supplying a husky 2
watts or more of audio power and will drive full-size communications
speakers to excellent volume levels.

The PTT switching circuit can be activated simply by introducing a
resistance (e.g. 10K) from the microphone input to ground. This resistan ce is
enough to trigger the PTT circuit without interfering with the microphone
audio input.

Consider these factors in selecting microphone, speaker and/or speaker­mike for FM voice operation. If your microphone and speaker preferences
differ radically from the use of a speaker/mike, and you do not wish to alter
the front panel, remember that you also have very easy access to mike and
speaker lines via J1, the packet connector.

A FEW ANTENNA CONSIDERATIONS

The idea of building your own transceiver is to save money and enjoy your
hobby. Effective VHF and UHF antennas are easy and inexpensive to build,
whether for fixed or mobile use. There are plenty of off-the-shelf antennas to
buy, but don't hesitate to "roll your own."

If you are a newcomer to ham radio, you'll discover many strong opinions
about the "best" antenna to use. A home-built ground plane vertical or even
a dipole can provide very satisfying results. Whether you need a gain factor
or directivity in your antenna depends on your operating goals. Regardless
of the style of antenna, it really pays to give serious attention to electrically­solid, weatherproof connections of the coaxial cable to the antenna
elements. A simple antenna in good condition will outperform a fancy one
that's been neglected.

Popular ham magazines and ARRL publications provide plenty of antenna
building ideas. MFJ Enterprises offers good value in simple ready-to-use
antennas for 2 Meters.

FX 146 • 16

VHF PACKET DATA OPERATION

Your FM transceiver was planned and designed to accommodate easy and
reliable VHF packet radio operation.

The J1 Packet I/O port can be quickly connected to many modern TNC's and
the Ramsey P-IBM or P64 Packet Modems with Radio Shack's shielded DIN
cable (42-2151). Otherwise, your first step is to prepare a reliable 5­conductor cable with a 5-pin DIN plug (RS 274-003) at one end, and the
correct connector needed by your packet TNC at the other end. If you
salvage a "ready made" 5-pin DIN cable from something like a discarded
computer joystick, be sure that there are indeed 5 wires, or at least the ones
that are required by your TNC!

Consult your Packet TNC or Packet Modem documentation for ALL details
on hookup and operation. Pin 4 of J1 offers a choice of amplified and
squelched (speaker level) audio output or low-level (discriminator) output.
This choice is set up by the jumper wire positions clearly visible on the PC
board.

Packet RX Audio Jumper: Some TNC's require low-level audio from the
discriminator output of the FM detector, while others will accept speaker
output. Either is available in the FX transceivers. Simply install a jumper in
the appropriate location near VR1, to connect "EXT AUDIO" to either
"SPKR" for speaker audio or "DATA" for discriminator audio. Use scrap
resistor wire to make the jumper. You also can choose to wire these three
points to a miniature SPDT switch which you can mount on the rear panel
near the packet connector. OR, use a PC mount switch in the jumper area
itself.

Use this space to diagram your TNC cable connection:

FX-146 • 17

RAMSEY FX-SERIES FM TRANSCEIVER
(With emphasis on the PLL and VCO)

MC13135

FX 146 • 18

FX-146 CIRCUIT OVERVIEW

The FX-146 VHF FM Transceiver circuit theory is explained in progressive
stages and in some detail as part of our "Learn As You Build" approach to
electronic kits. Builders are encouraged to study and learn about a stage or
section, build it and then test it before going to the next stage. The circuit
explanations are necessarily written for people with all levels of experience,
starting with and FAVORING beginners.

Following is a straight and "minimally chatty" synopsis or overview of FX­series technical information provided in the building stages. However, we'll
still follow the same stage-by-stage designations of the building process.

A: DC Power Input

Much of the circuitry operates on the regulated 8 volts supplied by voltage
regulator VR1. "+8R" or "+8T" are points where the regulated 8V output is
switched for Receive or Transmit by the PTT circuitry (Q12, U4c, U4d, Q13,
Q14).

The Receiver IC (U1) and the digital frequency synthesis circuit are powered
by +5 volts regulated by VR2. The op amps used in the circuit (U4 and U5)
operate from this single supply through the use of voltage divider networks
at the respective IC's. The full 12-15 volt input is supplied to the transmitter
RF output section and to the audio amplifier (U2).

Components L20 and C42 provide ignition noise filtering. The 5-pin DIN
Packet I/O Jack (J1) has pinouts corresponding to current conventions for
TNC's. Receiver audio to pin 4 may be taken from the amplified speaker
output, or from the FM discriminator output or from the true FSK data output
of U1. Selection is by a jumper wire on the PC-board.

B: Receiver Audio Amplifier

The LM380 is a self-contained general purpose audio amplifier capable of
over 2 watts audio output with a voltage gain of 50. Audio from from the FM
discriminator (U1) is fed through C7 through the 10K volume control (R7) to
pin 2, the amplifier input. The amplified output at pin 8 is available through
C34 to both the speaker jack and pin 4 of the Packet I/O Jack. C41 in series
with R108 across this amplified output are good practice recommended to
prevent self-oscillation of the IC. Pin 1 is bypassed to ground through C48 in
normal operation.

If pin 1 is grounded directly, the internal bias of the LM380 is upset, and the
amplifier is silenced. Q6 is a simple switch. When 8 volts is applied through
R107 and D22 to the base of Q6, the transistor collector grounds pin 1 of
U2, thus silencing the receiver during transmit. The COR output of U1 (pin

16) also mutes the amplifier.

FX-146 • 19

FX 146 • 20

Stage CR: Integrated FM Receiver

The MC13135 is a complete FM narrowband receiver from antenna input
(pin 22) to audio output (pin 17). The low voltage dual conversion design
results in low power drain, excellent sensitivity and good image rejection in
narrowband voice and data link applications. The FX146 implementation of
this IC yields increased image rejection by using a 21.4 MHz first IF rather
than the traditional 10.7 MHz.A precision 2-pole crystal filter (FL1) is used for
the 21.4 MHz first IF.

Our design injects the PLL controlled VCO output through C35 to pin 1
rather than using U1's internal local oscillator circuit. The VCO input to pin 1
is mixed with the RF input from the antenna circuitry.

The first mixer amplifies the signal and converts this RF input to 21.4 MHz.
This IF signal is applied to the second internal mixer via pin 18, where the
2nd IF frequency of 455 KHz is achieved by mixing with the 21.855 MHz
oscillator. The oscillator circuit is internal to U1; the crystal is Y1, 21.855
MHz.

The 455 KHz second IF output (pin 7) requires filtering. We used a precision
ceramic 455 KHz filter with 6 poles for a 2nd IF filtering scheme designed to
solve the adjacent- frequency swamping effect experienced with many
handhelds costing much more.

The receiver has good "hysteresis" characteristics, the ability to hold the
squelch open once it has been broken by a marginal signal, even if the
signal becomes weaker. The squelch is activated by signal strength, not by
noise.

R13 permits squelch adjustment. Finally, the carrier detect circuitry affords
the same COR ("Carrier Operated Relay") action as needed in any repeater,
which is why the output of pin 16 is also available on the PC board,
designated "COR."

Stage DR:

Antenna Input and RF Preamplifier: At Antenna jack J3, C71, L12 and C72
form a LOW pass filter, The filtered signals are coupled through C47 to be
amplified by Q3, NE021, favored for its high gain and low noise (15 db gain,
1 db noise).

Front-end components C30, L5, C28, L2, C31, L6 form a BANDPASS filter,
which sets both upper and lower limits on the RF passing from Q3 to Q2 for
further amplification and coupling via C17 to U1, pin 22.

The PIN diodes, D2, D6 and D7, perform all RF T-R functions. PIN diodes
can pass RF energy either way when turned on by DC voltage and also
block RF from the other direction when not powered by DC. During Receive,
D6 is "on" and permits RF to flow from the antenna through C47 to the
amplifier stage just discussed. Because any DC device needs a ground

FX-146 • 21

connection as well as +DC, D6 is grounded through RF choke L17, which
prevents the antenna RF from being shorted to ground.

During Transmit, D7 passes RF from the transmitter to the antenna, and L17
again prevents loss of RF to ground. During transmit, D6 is blocking
transmitter RF from the receiver circuit. For maximum protection of the more
delicate receiver circuit, D2 is turned on during transmit to ground any stray
RF.

Stage E-F The FX Transceiver VCO

The VCO (Voltage Controlled Oscillator) provides basic frequency control for
both transmit and receive modes. It is essential to understand its function in
the transceiver circuit. Q7 is the oscillator transistor. L7, D3 and D23 are key
VCO components.

After the VCO is assembled on the PC board, the interested builder is given
the option of experimenting with it in receive mode before working on the
PLL synthesizer. This is done by applying a variable DC control voltage
through a pot to TP1. Otherwise, TP1 is available for checking VCO control
voltage during initial alignment. TP2 permits checking VCO frequency output
with a frequency counter. TP3 permits checking the output of the TD6128
Ã64/65 dual modulus prescaler (U3)

The control voltage for the D3 and D23 varactor diodes is supplied through
R47 and R25 by the output of U5:A in the PLL synthesizer circuit.

There must be a 21.4 MHz difference between the receive and transmit
frequencies of the VCO. This swing cannot be accomplished by PLL
programming alone. The VCO must be able to stay "in range" with the
synthesizer. D3 and D23 work in series during transmit, which reduces their
capacitance per the standard formula. For example, if a given control voltage
runs both diodes at 5 pf, the actual capacitance is 2.5 pf. In receive, the +8R
through D1 causes D3 to be shunted by C39, which causes D23 alone to
control the VCO L-C circuit, introducing twice as much capacitance and
thereby lowering the frequency.

Q5 is a common base buffer which affords good isolation, low input
impedance and broadband characteristics. The buffered outp ut from Q5 is
fed into U3, TD6128, a dual modulus Ã64/65 prescaler, the output of which
is fed to the A and N counters in U6. The output is further buffered and
amplified by Q16, the VCO buffer which couples through C35 for receive,
and Q10 through C56 for transmit.

The VCO is is frequency modulated by microphone amplifier U4. D5 and
R31 perform an interesting function. Remember that the VCO control voltage
has a range of about 1.0 volts DC (low frequency) to 7.0 volts (high
frequency). Therefore, more modulation voltage is needed at the higher
frequencies. As the VCO control voltage increases, D5 turns on and places
R31 in parallel with R33, reducing the resistance in the line to half and

FX 146 • 22

thereby increasing available modulation voltage.
The VCO requires a very pure source of well-filtered DC, free of AC hum,

alternator whine or other disturbance. R19 and the 47 uf C40 form a basic
low pass filter. Transistor Q4 serves as an electronic capacitance multiplier.
The actual effect of the filter is that the beta of Q4 multiplies the 47 uf for a
virtual capacitance effect of a much larger device.

Stage G: The FX- Transceiver Synthesizer PLL

The MC145152 IC incorporates the equivalent of 8000 individual transistors
and contains the following circuits:

• A crystal reference oscillator governed by Y2, 10.24 MHz.

• A counter or "frequency divider" circuit set externally to divide the

crystal oscillator output by 2048, for a Reference Frequency output
of 5 KHz.

• A second counter or frequency divider that divides the frequency

from the Prescaler (U3) by the externally programmed number that
we call "N".

• A third frequency divider ("A") also used for programming

• Control logic circuitry which permit the "N" and "A" counters to

work together for channel programming.

• The Phase Detector (or "phase corrector") which compares the 5

KHz Reference Frequency with the "intended" 5 KHz output of the
N-divider and sends correcting pulses to the VCO to keep the
output of the N-divider right at 5 KHz.

• A "lock detect signal" circuit. The reference oscillator is internal to

U6, governed by Y2.

The precision of the 10.240 MHz reference oscillator can be adjusted by
trimmer C81. The R divider feeds 5 KHz to the phase detector section of U6
(10240 KHz divided by 2048).

The output of the TD6128 Ã64/65 prescaler U3 is AC coupled via C57 to pin

1. U3 is a dual modulus prescaler, controlled by pin 9 of U6. The prescaled
output of the VCO is fed to the A and N counters. The "N" number
programmed on the diode matrix is predetermined to divide this frequency
down to 5 KHz for phase comparison with the 5 KHz output of the crystal
controlled reference divider. Maximum "N" is 65,535, achieved by switching
on all 16 parallel inputs.

Unlike simpler PLL IC's, U6's phase detector has TWO outputs at pins 7
and 8. These outputs go through very simple low pass filters (R44-C68, R53­C91) to cut back the 5 KHz whine sound of U6 at work. Op amp U5:A sums
together the phase detector outputs and the output of U5:A is passed
through a network of 2.2 uf electrolytic capacitors (C67,70,90,92) to smooth
out the phase detector pulses to clean DC for controlling the VCO.

FX-146 • 23

FREQ. N = BINARY PROGRAMMING VALUES

144.000 28,800

148.000 29,600

0111 0000 1000 0000

0111 0011 1010 0000

R48 and C85 form yet another low pass filter to ensure that any 5 KHz
"whine" will not get into the VCO. Because the DC charge developed in C85
(.1 uf) would slow down the PLL during major frequency swings, such as just
going from transmit to receive, D8 and D10 are set up back-to-back across
voltage dropping R48. Whenever there is a major frequency shift (which
means a significant VCO control voltage change), one way
or the other, one diode or the other is switched on to
short out R48 and discharge C85. This lets the PLL

146520 (KHz)

5 (KHz)

relock instantly; C85 recharges and the diodes become
no factor in the circuit.

The lock detect output (pin 28) gives a strong series of pulses when the PLL
is unlocked. When the PLL is locked, only a tiny sawtooth wave appears at
pin 28. The "lock detect" voltage is watched by U5:B. If "unlock" pulses
appear, they are integrated through R90 and C96 as a fairly clean DC
voltage charge built up in C96. If this charge causes U5B to swing low, bias
is removed from Transmit Buffer Q10, preventing transmitter damage and
unwanted emissions.

Stage H: The Diode Matrix and PLL Synthesizer Programming

There are two diode-matrix programming areas on the PC board. The
obviously larger area is for frequency channel programming. The second
space is for offset programming added in by U7-U10.

The 19 100K resistors at the frequency programming matrix and the 14
100K resistors at the offset matrix are "pulldown resistors," to ensure
positive logic switching action of U6.

Q15 and its associated switching diodes ensure that the desired offset is
switched in during transmit, that offset programming does not interfere when
simplex is desired and that the offsets do not interfere with receiver
operation and that receiver programming (21.4 MHz lower) does not
interfere with transmit operation.

A variety of techniques are possible for binary programming of U6's 16
paralel inputs. We focus on the diode programming approach with some
brief suggestions on externally-controlled switching. It is very intentional on
our part to leave innovative programming schemes up to FX transceiver
users, because there's no single best way to do it for everybody.

FX 146 • 24

There are several methods for quickly finding the required binary code for a
particular frequency and its "N" number:

1. Descending Subtraction (see Programming Worksheet)

2. Printed reference lists (see Popular 2 Meter Frequency Pairs)

3. Computer programs (see our sample BASIC program)

We recommend strongly that you fully understand how to make the
calculation yourself, because that is your ONLY means for checking the
accuracy of printed information, computer programs or the operation of
experimental programming circuits. Even though there are 16 matrix
positions to program, there are some shortcuts to make the job easier for
normal ham band operation. Consider the upper and lower band edges.
Notice the values of the highest 6 positions are the same throughout the
band. We still must program in those six positions but we only need to
calculate for the remaining 10 (512 through 1) to program any 2 Meter band
frequency desired. The simplex calling frequency of 146.52MHz is the
demonstration and alignment standard for the FX-146 model.

"N" is quite easy to determine:
"N" for 146.520 MHz = = 29,304

The placement of diodes in the Programmable Offset Matrix follows the
same binary number principles as used for frequency programming. This
matrix is connected to the 16 programming inputs of U6 through the four 4
bit binary adders (U7-U10). Fewer programming positions are provided on
the board simply because there is no practical use for extremely large or
very tiny offsets. The 1 bit to 8K range provides plenty of flexibility for non­standard channel spacing.

U7 through U10 are called "4 bit" binary adders because they each can
handle four binary addition operations. For each bit, there are A and B inputs
and one S (sum) output. Examine the schematic diagram closely, and you
will see that all the frequency programming lines are connected to "A" inputs
and all offset lines go to "B" inputs. Notice further that the binary positions of
both matrixes correspond to each other exactly: the 8K offset position goes
to B1 of U7 and the 8K frequency programming position goes to A1. Their
sum appears at S1 (pin 1) and goes to U6. And so forth for all the other
binary programming positions.

The programming for receive mode and standard repeater offsets is
silkscreened on the PC board itself. Assembly Stage H explains the theory
behind these positions. The +RPT "N" numbers are calculated in the same
way as for the Frequency Programming matrix. -RPT, RECV and other
"minus" offsets are calculated by straightforward "2's Complement" binary
addition. See Stage H for examples.

FX-146 • 25

Stage M: Microphone Amplifier and PTT Circuit

U4 is a LM324 quad op amp: two are used as a conventional microphone
gain amplifier, and the other two are used in the PTT (push to talk) circuit.

Capacitor C83 couples microphone audio to U4A and isolates the audio
(AC) from the PTT circuitry (DC). U4 is powered by a single +8V supply
through the use of a voltage divider network (R59, R40). The gain of the
amplifier is established by the ratio of R56 to R58. A passive low pass filter
is formed by R51 and C89. The B section of U4 and its associated
components form an active low pass audio filter. The output of U4B is fed
through C62 to modulate the VCO control voltage as explained in Stage E-F.
Trimmer R46 adjusts modulation level.

The purpose of Q11 is to shunt the microphone circuit straight to ground
during receive, so that it cannot possibly disturb the VCO. An accessory
modulation input is provided at PC-board point "PL" for direct injection of
DTMF or CTCSS tones, etc. The PTT circuit is designed to accommodate
the popular ICOM compatible speaker-mikes. Notice that a single line at J4
serves both audio and PTT functions. One shielded wire into the microphone
handles THREE functions. First, we need to supply audio output from the
microphone element to the amplifer. Secondly, we need some kind of PTT
switching connection. Third, the electret microphone itself needs a small
amount of voltage to operate its internal FET source follower transistor.

Here's how we do it with one mike line. Pushing the button simply connects
the microphone element to the line. About 2 volts through R60 and R57
operate the microphone element which sends audio through C83 to U4A.
PNP transistor Q12 senses the tiny current draw of the microphone element
and switches the 8 volts at the emitter through to the collector. To state it
very simply, the output of U4 turns off PNP Q13 which had been supplying 8
volts to all "+8R" points of the circuit. And the output of U4C switches on
PNP Q14 to supply all "+8T" points. Zener diodes D11 and D12 assure
positive action, that Q13 and Q14 are fully on or fully off when the op amp
outputs swing. Releasing the mike button instantly reverses the status of
Q12, Q13 and Q14 to return to receive mode. R70 limits the current drawn
by "TX" indicator D17 to a safe level.

The PTT circuit may also be activated at pin 3 of the Packet I/O jack. A
direct short to ground is not necessary. The author noted very positive PTT
action with resistance as high as 100K from pin 3 to ground.

Stage TX: Transmitter Buffer, Driver and Final

The transmitter section, Q10, Q9 and Q8, is conventional VHF RF circuitry
that has proven quite reliable in Ramsey FM transceivers. Just a few circuit
notes are in order.

Transistor Q10, the transmit buffer, amplifies the VCO output from C56 to
about 10 milliwatts, quite sufficient for checking modulation and PLL

FX 146 • 26

Using the FX-series FM Transceiver Quick Reference Programming
Guide:

In addition to "pencil & paper math" calculation directions and also a handy
computer BASIC program for programming the FX- series Transceiver for
any frequency and transmit offset within its specified range, we provide this
guide for binary programming of a variety of popular Repeater frequency
pairs as well as some other frequencies of general interest. All binary
programming data for 512 through 1 presumes prior diode programming of
higher level binary inputs which remain constant for the 2 Meter amateur
radio band:

32K 16K 8K 4K 2K 1K

0 1 1 1 0 0

You'll notice definite patterns
in the standard repeater
frequency assignments and
their binary equivalents. Look

at these patterns up and
down the programming input rows as well as across for any given frequency.
If your application could use more than the 12 channels easily programmed
for front panel switching, perhaps these patterns will give you some good
ideas for additional channel switching convenience.

FX-146 • 27

FX-146 Quick Program Reference
Standard 2 Meter band repeater pairs and selected frequencies

Program as follows:

1. Install diodes at 16K, 8K, 4K and NO diodes at 32K, 2K ,1K positions.

2. PLUS install diodes at 512 through 1 positions as needed per this Quick
Reference Chart.

3. For repeater channels, add the proper repeater TX offset diode.
Simplex channels: add the 'SIMP' diode.

4. A '1' means to install a diode, '0' means NO diode.

Freq Offset N 512 256 128 64 32 16 8 4 2 1

145.11

145.13

145.15

145.17

145.19

145.21

145.23

145.25

145.27

145.29

145.31

145.33

145.35

145.37

29,022 0 1 0 1 0 1 1 1 1 0

-

29,026 0 1 0 1 1 0 0 0 1 0

-

29,030 0 1 0 1 1 0 0 1 1 0

-

29,034 0 1 0 1 1 0 1 0 1 0

-

29,038 0 1 0 1 1 0 1 1 1 0

-

29,042 0 1 0 1 1 1 0 0 1 0

-

29,046 0 1 0 1 1 1 0 1 1 0

-

29,050 0 1 0 1 1 1 1 0 1 0

-

29,054 0 1 0 1 1 1 1 1 1 0

-

29,058 0 1 1 0 0 0 0 0 1 0

-

29,062 0 1 1 0 0 0 0 1 1 0

-

29,066 0 1 1 0 0 0 1 0 1 0

-

29,070 0 1 1 0 0 0 1 1 1 0

-

29,074 0 1 1 0 0 1 0 0 1 0

-

145.39

145.41

145.43

145.45

145.47

29,078 0 1 1 0 0 1 0 1 1 0

-

29,082 0 1 1 0 0 1 1 0 1 0

-

29,086 0 1 1 0 0 1 1 1 1 0

-

29,090 0 1 1 0 1 0 0 0 1 0

-

29,094 0 1 1 0 1 0 0 1 1 0

-

FX 146 • 28

145.49

29,098 0 1 1 0 1 0 1 0 1 0

-

146.61

146.64

146.67

146.70

146.73

146.76

146.79

146.82

146.85

146.88

146.91

146.94

146.97

147.00 + 29,400 1 0 1 1 0 1 1 0 0 0

147.03 + 29,406 1 0 1 1 0 1 1 1 1 0

29,322 1 0 1 0 0 0 1 0 1 0

-

29,328 1 0 1 0 0 1 0 0 0 0

-

29,334 1 0 1 0 0 1 0 1 1 0

-

29,340 1 0 1 0 0 1 1 1 0 0

-

29,346 1 0 1 0 1 0 0 0 1 0

-

29,352 1 0 1 0 1 0 1 0 0 0

-

29,358 1 0 1 0 1 0 1 1 1 0

-

29,364 1 0 1 0 1 1 0 1 0 0

-

29,370 1 0 1 0 1 1 1 0 1 0

-

29,376 1 0 1 1 0 0 0 0 0 0

-

29,382 1 0 1 1 0 0 0 1 1 0

-

29,388 1 0 1 1 0 0 1 1 0 0

-

29,394 1 0 1 1 0 1 0 0 1 0

-

147.06 + 29,412 1 0 1 1 1 0 0 1 0 0

147.09 + 29,418 1 0 1 1 1 0 1 0 1 0

147.12 + 29,424 1 0 1 1 1 1 0 0 0 0

147.15 + 29,430 1 0 1 1 1 1 0 1 1 0

147.18 + 29,436 1 0 1 1 1 1 1 1 0 0

147.21 + 29,442 1 1 0 0 0 0 0 0 1 0

147.24 + 29,448 1 1 0 0 0 0 1 0 0 0

147.27 + 29,454 1 1 0 0 0 0 1 1 1 0

147.30 + 29,460 1 1 0 0 0 1 0 1 0 0

147.33 + 29,466 1 1 0 0 0 1 1 0 1 0

147.36 + 29,472 1 1 0 0 1 0 0 0 0 0

147.39 + 29,478 1 1 0 0 1 0 0 1 1 0

FX-146 • 29

Freq = Receive frequency/Repeater output N = Frequency (KHz) ÷ 5

145.01 S 29,002 0 1 0 1 0 0 1 0 1 0

145.03 S 29,006 0 1 0 1 0 0 1 1 1 0

145.05 S 29,010 0 1 0 1 0 1 0 0 1 0

145.07 S 29,014 0 1 0 1 0 1 0 1 1 0

145.09 S 29,018 0 1 0 1 0 1 1 0 1 0

KHz

145.01 - 29,002 1 0 1 0 0 0 1 1 0 1

145.03 - 29,006 1 0 1 0 0 1 0 1 1 1

145.05 - 29,010 1 0 1 0 0 1 1 0 1 1

145.07

145.09 + 29,018 1 0 1 1 0 1 0 1 1 1

145.05 + 29,010 1 0 1 1 1 0 1 0 1 1

145.07 + 29,014 1 1 0 0 0 0 0 0 0 1

145.09 + 29,018 1 1 0 0 1 0 0 1 1 1

-

29,014 1 0 1 0 1 1 0 0 0 1

Some common PACKET frequencies:
NASA STS Orbiters and USSR MIR transmit on:

and may also listen on various frequencies for which an auxiliary offset can

145.55 - 29,110 0 1 1 0 1 1 0 1 1 0

be programmed on your FX-146.

146.52 S 29,304 1 0 0 1 1 1 1 0 0 0

National Simplex frequency:

RAMSEY FX-series Programming Worksheet

To convert N from decimal to binary, simply TRY to subtract EACH of the 16
binary values from N, always in descending order, always starting with
32768 and always ending with 1. This process will always yield 16 YES or
NO answers, which will give you exact diode installation instructions.

N = Freq in KHz divided by 5 KHz (or, Freq in MHz divided by .005)

FX 146 • 30

Let's try doing an example. We want to receive 146.520 MHz:

Subtracting from N: Remainders & Doodles NO YES Position
Can you subtract 32768?

Can you subtract 16384?
Can you subtract 8192?
Can you subtract 4096?
Can you subtract 2048?
Can you subtract 1024?
Can you subtract 512?
Can you subtract 256?
Can you subtract 128?
Can you subtract 64?
Can you subtract 32?
Can you subtract 16?
Can you subtract 8?
Can you subtract 4?
Can you subtract 2?

32768
16384

8192
4096
2048
1024

512
256
128

64
32
16

8
4
2

Can you subtract 1?

Will this be a Simplex chan­nel?

Will Transmit be 600 KHz
LOWER than Receive?

Will Transmit be 600 KHz
HIGHER than Receive?

1

SIMP

- RPT

+ RPT

N = 146520 ÷ 5 = 29,304 Now, convert to binary...
Install diodes in YES positions only.

See FX-series instruction book, Section H, for ham band shortcuts for 32K
through 1K programming positions. If an auxiliary split is needed or if you are
not licensed to transmit in a band portion, do not install diodes in SIMP,

FX-146 • 31

+RPT or -RPT positions.
Using Computer BASIC as a Diode Matrix Programming Aid
The purpose of the following BASIC program is to be as CLEAR AND

GENERIC as possible with no concern for programming efficiency or
sophistication. Those who enjoy and understand programming in Basic can
dress it up to suit themselves. Or, they can write a program that satisfies
their own standards. A major purpose of the deliberate simplicity is that the
routine should run on virtually any computer using any version of Basic. If
you follow the program flow, you'll see that it carries out in order the very
same steps you would follow by hand in converting decimal to binary using
the FX Programming Worksheet. You can use this same program for
calculating nonstandard Transmitter Offsets.

Program Notes:

1. Install diodes ONLY in rows where "1" is indicated.

2. If you prefer, "0's" can also be generated through the use of appropriate
IF . . . THEN . . . ELSE lines.

3. The "!" after 32768 is generated automatically by the computer, whether
you type it in or not.

4. Be VERY accurate in typing "<" and ">" or "=>" because they are critical
to correct placement of 1's.

5. The CLEAR instruction after screen printing is important; if it is omitted,
AA, BB, CC, etc., will not be reset for checking the next frequency.

6. Innovative computer programs to enhance enjoyment of the FX
transceivers are encouraged; send them to your favorite ham or computer
magazine, newsletter or BBS.

7. LPRINT or equivalent Basic statements can be used to produce
hard-copy printouts of frequency information you need.

8. IMPORTANT: Before soldering ANY diodes in your FX-transceiver
programming matrix per this program, CHECK AND VERIFY that your
program is giving CORRECT results! COMPARE it to the samples in this
book.

NOTICE:
Although this program has been tested on many Microsoft BASIC
releases, including GW Basic, it is printed here solely as a convenience
and is not integral to the Ramsey FX-146 operation. If you have trouble
running the program, please get help from a local computer friend and
not from the Ramsey factory - we're radio guys, not computer hackers!

Sample BASIC Program Listing

FX 146 • 32

50 PRINT “Enter Receiver Frequency as 6 digits with NO decimal!”
52 INPUT “For example: 146520. Enter here: “; F
55 N = F/5
60 PRINT “The FX146 or FX220 N number for binary conversion is “; N
101 AA = 0
102 BB = 0
103 CC = 0
104 DD = 0
105 EE = 0
106 FF = 0
107 GG = 0
108 HH = 0
109 II = 0
110 JJ = 0
111 KK = 0
112 LL = 0
113 MM = 0
114 NN = 0
115 OO = 0
116 PP = 0
200 IF N => 32768! THEN AA = 1
205 IF N > 32768! THEN NA = N - 32768!
206 IF N < 32768! THEN NA = N
210 IF NA => 16384 THEN BB = 1
215 IF NA > 16384 THEN NB = NA - 16384
216 IF NA < 16384 THEN NB = NA
220 IF NB => 8192 THEN CC = 1
225 IF NB > 8192 THEN NC = NB - 8192
226 IF NB < 8192 THEN NC = NB
230 IF NC => 4096 THEN DD = 1
235 IF NC > 4096 THEN ND = NC - 4096
236 IF NC < 4096 THEN ND = NC
240 IF ND => 2048 THEN EE = 1
245 IF ND > 2048 THEN NE = ND - 2048
246 IF ND < 2048 THEN NE = ND
250 IF NE => 1024 THEN FF = 1
255 IF NE > 1024 THEN NF = NE - 1024
256 IF NE < 1024 THEN NF = NE
260 IF NF => 512 THEN GG = 1
265 IF NF > 512 THEN NG = NF - 512
266 IF NF < 512 THEN NG = NF
270 IF NG => 256 THEN HH = 1
275 IF NG > 256 THEN NH = NG - 256
276 IF NG < 256 THEN NH = NG
280 IF NH => 128 THEN II = 1
285 IF NH > 128 THEN NI = NH - 128
286 IF NH < 128 THEN NI = NH
290 IF NI => 64 THEN JJ = 1
295 IF NI > 64 THEN NJ = NI - 64
296 IF NI < 64 THEN NJ = NI
300 IF NJ => 32 THEN KK = 1
305 IF NJ > 32 THEN NK = NJ - 32
306 IF NJ < 32 THEN NK = NJ
310 IF NK => 16 THEN LL =1
315 IF NK > 16 THEN NL = NK - 16
316 IF NK < 16 THEN NL = NK
320 IF NL => 8 THEN MM = 1
325 IF NL > 8 THEN NM = NL - 8

FX-146 • 33

326 IF NL < 8 THEN NM = NL
330 IF NM => 4 THEN NN = 1
335 IF NM > 4 THEN NX = NM - 4
336 IF NM < 4 THEN NX = NM
340 IF NX > 2 THEN OO = 1
345 IF NN = 2 THEN OO = 1
346 IF NX = 3 THEN PP = 1
347 IF NX = 1 THEN PP = 1
400 PRINT “32768 - “; AA
405 PRINT “16384 - ”; BB
410 PRINT “ 8192 - “; CC
415 PRINT “ 4096 - “; DD
420 PRINT “ 2048 - “; EE
425 PRINT “ 1024 - “; FF
430 PRINT “ 512 - “; GG
435 PRINT “ 256 - “; HH
440 PRINT “ 128 - “; II
445 PRINT “ 64 - “; JJ
450 PRINT “ 32 - “; KK
455 PRINT “ 16 - “; LL
460 PRINT “ 8 - “; MM
465 PRINT “ 4 - “; NN
470 PRINT “ 2 - “; OO
475 PRINT “ 1 - “; PP

480 PRINT “The Binary Equivalent of N can also look like this: “
481 PRINT “_______________________________________ “
482 PRINT USING “##”; AA, BB, CC, DD, EE, FF, GG, HH, II, JJ, KK, LL, MM, NN, OO, PP
485 PRINT
505 CLEAR.
510 GOTO 50
520 END

Here’s an example of the screen display for the program as written, showing
the results for an entry of “146865” and ready for the next frequency to be
entered as 6 digits:

The FX146 or FX220 N number for binary conversion is: 29373
32768 - 0
16384 - 1
8192 - 1
4096 - 1
2048 - 0
1024 - 0
512 - 1
256 - 0
128 - 1
64 - 0
32 - 1
16 - 1
8 - 1
4 - 1
2 - 0
1 - 1
>> The Binary Equivalent of N looks like this:
———————————————————-

For example: 146.52 MHz. = 146520. Enter here >>> ? 146865

FX 146 • 34

0 1 1 1 0 0 1 0 1 0 1 1 1 1 0 1

1 2

8 9 1

1

>>> Enter Next Frequency for Programming:
Enter Receiver Frequency as 6 digits with NO decimal!
For example: 146.52 MHz. = 146520. Enter here >>> ?

HOW TO ACTIVATE AN AUXILIARY OFFSET:

1. Install NO diode in SIMP, -RPT or +RPT for the channel that gets a non­standard offset.

2. Program the AUX matrix row for the desired offset, following our
published instructions.

3. Connect the channel row to the AUX matrix row by installing a diode as
shown below. The cathode end is soldered to the diode programming
bridge. In this example, Channel 3 uses the auxiliary offset:

4. You can connect as many of the channel rows as you wish in this
manner, but remember that each would follow the same non-standard
split you have programmed. Only one such split can be programmed in
the AUX matrix row. It may be changed as needed. If more than one
non-standard split is needed, you can either give up a standard split or
devise your own way of switching in what you need.

4

DIODE JUMPE R FOR CHANNEL 3
PER MARKINGS ON PC BOARD

SIMP

-RPT

+RPT

32 K
16 K

5

3

6 7

0

1 12

FRONT EDGE OF PC BOARD

+TX (+RPT) OFFSETS

+TX offsets are programmed exactly like the Frequency Programming
matrix. For example, for a +600 KHz offset:

N= 600 KHz ÷ 5 KHz = 120

FX-146 • 35

PROGRAMMING THE 'MINUS' OFFSETS

We showed the Plus offsets first to prepare you for the Minus offsets. The
offsets are entered into the FX synthesizer through the binary adders, U7-

10. Notice that we said adders and not subtractors; in binary there is 'no
such animal' as a subtractor. We must use the technique known as 'two's
complement addition' which actually performs a subtraction process! This
may sound complicated, but it really isn't. We simply find 'N' as usual, take
its 'two's complement' and program the result into the offset matrix. We'll
show you three detailed examples.

Don't be alarmed. If all you need is the standard 2 Meter band offsets, just
install the diodes in the offset matrix as clearly illustrated on your PC board.
Understanding the following information is essential ONLY for those who
need to program non-standard Minus or AUX offsets.

First we need to understand some rules for binary addition:

1) 0+0=0

2) 1+0=1

3) 1+1=0 and CARRY 1
(Carrying is done from right to left)

EXAMPLE 1: -600 KHz TX Offset

As for the +600 KHz offset, N= 600 ÷ 5 KHz = 120. However, this is the last
of Decimal numbers in this work. We'll have to work with Binary numbers
now. In brief, we set up the complement, or exact inverse of N in binary, and
then add 1. This will give us our two's complement that is needed for
programming into our offset matrix.

Binary code for N=120

8192 4096 2048 1024 512 256 128 64 32 16 8

0 0 0 0 0 0 0 1 1 1 1
Now, just INVERT all of the above 'bits':
1 1 1 1 1 1 1 0 0 0 0

Then, ADD 1:
1 1 1 1 1 1 1 0 0 0 1
This is our two's complement value which we program into our offset matrix.

You'll see these diodes in the position for -600 KHz TX offset.
Even though it appears that we are adding a huge N number to the original

transmitter frequency, the binary adders will follow the rules of binary
addition and provide the proper programming information to the PLL
synthesizer.

FX 146 • 36

EXAMPLE 2: RECEIVER OSCILLATOR FREQUENCY

We know from previous circuit discussion that the PLL synthesizer must run

21.4 MHz lower when in receive mode. Two things must be done to do this;
first, we switch out varactor diode D3 to allow the VCO L-C circuitry to tune

21.4 MHz lower, and secondly, program in a 'minus' 21.4 MHz offset to the
synthesizer. This offset is permanently programmed into the matrix because
the 21.4 MHz 1st IF is integral to the FX receiver design. Look closely at the
Receive offset diode row and see why the diodes are installed the way they
are.

N = 21400 ÷ 5 KHz = 4,280
Binary code for N=4,280

8192 4096 2048 1024 512 256 128 64 32 16 8

0 1 0 0 0 0 1 0 1 1 1

Now, invert all the bits:
1 0 1 1 1 1 0 1 0 0 0

Add 1:
1 0 1 1 1 1 0 1 0 0 1

You'll see this is the number programmed into the Receive offset matrix line
for a minus 21.4 MHz offset.

EXAMPLE 3. TWO'S COMPLEMENT WITH CARRY

For illustration purposes, we'll pick an odd-ball offset such as 640 KHz. In
this case, N = 640 ÷ 5 KHz = 128.

8192 4096 2048 1024 512 256 128 64 32 16 8

0 0 0 0 0 0 1 0 0 0 0

Invert all bits: 1 1 1 1 1 1 0 1 1 1 1

Add 1: + 1

Sum at '8' bit position, carry 1 1 0
Sum at '16' bit position, carry 1 1 0 0
Sum at '32' bit position, carry 1 1 0 0 0
Sum at '64' bit position, carry 1 1 0 0 0 0

Sum at '128', no carry needed 1 0 0 0 0

Final result: 1 1 1 1 1 1 1 0 0 0 0

Binary code for N=128

FX-146 • 37

FX-146 PROGRAMMING SUMMARY

Programming your FX-146 is really quite simple; all it takes is a clear mind, a
scratch pad and a calculator. In closing, let's find the proper N value for a
common NOAA weather channel, 162.55 MHz.

First, find N: 162550 ÷ 5 = 32,510 Then, convert to binary:
Can we subtract 32,768? NO

Can we subtract 16,384? YES 32,510 - 16,384 = 16,126
Can we subtract 8,192? YES 16,126 - 8,192 = 7,934
Can we subtract 4,096? YES 7,934 - 4,096 = 3,838
Can we subtract 2,048? YES 3,838 - 2,048 = 1,790
Can we subtract 1,024? YES 1,790 - 1,024 = 766
Can we subtract 512? YES 766 - 512 = 254
Can we subtract 256? NO
Can we subtract 128? YES 254 - 128 = 126
Can we subtract 64? YES 126 - 64 = 62
Can we subtract 32? YES 62 - 32 = 30
Can we subtract 16? YES 30 - 16 = 14
Can we subtract 8? YES 14 - 8 = 6
Can we subtract 4? YES 6 - 4 = 2
Can we subtract 2? YES 2 - 2 = 0
Can we subtract 1? NO

We're done! Install diodes in all YES positions, and no diodes elsewhere.

BASICS OF EXTERNALLY CONTROLLED FX-TRANSCEIVER
FREQUENCY SWITCHING

The 12 front panel switched channels, with never a need for a crystal will
cover most applications generously. Yet many of us will want to figure out
ways for easy frequency-programming of still more channels, especially if we
do a lot of cross-country travel. Rather than endorse or illustrate any
particular scheme, of which there are dozens if not hundreds, we provide
here the most basic schematic information needed to set up any kind of
auxiliary switching correctly. The principles and requirements remain the
same whether you use DIP switches, toggle or slide switches, electronic
latching or go all out to build the mother of all diode matrixes. Make sure
whatever you build resembles electrically the diagram on the page 39.

Some DO's and DON'Ts of FX-Transceiver Add-Ons:

1. DO study and understand the basic switching diagram.

2. DO let your ingenuity run wild to come up with the neatest, most cost­effective scheme.

3. Please DON'T ask our technicians to talk you through your own idea.

FX 146 • 38

FX-XCVR

PC BOARD

CONNECTION

1
2
4

8

16

32
64

128
256

512

1 K

2 K

4 K
8 K

16 K
32 K

+ RPT

- RPT
SIMP

+ 5V
GND

RIBBON CABLE

1N914/
1N4148

SWITCH:
SPST

4. DON'T run switching cables
across the VCO and Transmit
RF side of the PC board.

5. Please DO submit successful
frequency control ideas as
articles for your favorite ham
radio magazine. Your pay as
author may cover the cost of
your transceiver!

6. Please DO mail or fax us
your good ideas.

7. Please DON'T try out ANY
modifications of the basic FX­Transceiver unless you already
have it WORKING fine.

NOTES:

1. DIP switches with diodes
can be installed on/above the
diode matrix itself for E-Z
internal programing changes.

2. Any auxiliary programming
device can be wired to a
switched position on the FX­transceiver matrix as well as to
the auxiliary points illustrated.

3. "SPDT" switching may be
devised to select offsets.

4. Programming Shortcuts are
possible for ham-band
operation. (See text).

FX-146 • 39

FX-SERIES TRANSCEIVER GLOSSARY
The following is a deliberately INFORMAL collection of:

• Technical terms useful to know in understanding your FX- transceiver
design.

• Acronyms (phrases expressed by first letters of words: example: PLL
= Phased Locked Loop)

• Selected Electronics Industry "jargon"

Any of these words or expressions might be used in this instruction manual
or in conversation related to your FX- transceiver, either with other hams or
with Ramsey technicians. These descriptions or notes for a very few terms
certainly are not an "electronics dictionary," but the author/compiler hopes
that they might enhance your grasp of the concepts and language that he
has seen as useful in building and using this transceiver. For more detail,
PLEASE study the introductory part of each Assembly Stage.

ADDER = Anybody who can add can be called an "adder." If we delegate
such work to electronic devices, the most fundamental digital operation after
being in a binary high or low (on or off) state is to be able to find the sum of
such states from two or more sources. The BINARY ADDER performs this
function. See also: BINARY.

AFSK = "Audio Frequency Shift Keying." [SEE: "FSK"] In short, this is a
very popular form of data transmission.

AXIAL-LEAD = Wires stretch out from two opposite ends of a part instead of
from one end, i.e. along the "axis" of the body. For example: L20.

BA- = Manufacturer's PREFIX for PIN-type diodes.
BASIC = "Basic." We're talking about the one computer programming

procedure that should make sense to ALL computer owners. If any further
explanation is needed, visit a library or computer dealer.

BB- = Manufacturer's PREFIX for VARACTOR diodes.
BINARY = the number system based on the two values of 0 and 1. Here are

all the tables that we need to memorize:
0 + 0 = 0 0 + 1 = 1 1 + 1 = 0 and carry 1 to next

position.

BOARD = Generally refers to "PC board" or "printed circuit board."
BUFFER = An electronic circuit stage, a sort of "referee" that tells its input

and output not to mess with each other.Think about such a task! It may also
provide amplified output of the incoming signal.

CASCADE, cascading = combining two or more identical circuit elements or
components for improved effectiveness.

CARRIER = Transmitted RF signal that is NOT "modulated." It is heard as a
steady tone on BFO-equipped receivers or as a powerful silence (i.e. over
riding all background noise or hiss) on FM receivers.

FX 146 • 40

CCW = see CW below.
COR = "Carrier Operated Relay," a switching circuit activated by the

detection of a carrier signal in a receiving circuit.
"CW" = TWO common meanings in electronics: "Continuous Wave" for the

communicating of Morse code signals, or "Clockwise" to designate a point
on a variable control. "CCW" therefore means "counterclockwise."

DECIMAL = in computer or programming context, "decimal" refers to
counting by tens, our traditional way, in contrast to your computer's binary
(counting by 1's and 0's), or the hexadecimal system (counting by 16's.) See
"N" and BINARY.

DIP = "Dual Inline Package," referring to IC's and their sockets or any other
component ("DIP Switch," etc.). The "line" refers to rows of PC-board or
perfboard holes that are 0.1" apart. "Dual" means two rows. Therefore "SIP"
would mean a SINGLE row device.

DISCRIMINATOR = FM terminology for "detector." See: FM.
DUAL-MODULUS = as in dual-modulus prescaler or divider: a circuit which

divides a frequency by two different ratios depending on pin selection, for
example: 64 or 65. (See: PRE- SCALE)

FILTER-ACTIVE
FILTER-CERAMIC
FILTER-CRYSTAL Filters are used in DC, Audio and RF
FILTER-HI-PASS circuits. Understanding them is essential
FILTER-LOW-PASS electronics know-how. The Radio Amateurs’
FILTER-BANDPASS Handbook covers the subject of filters very
FILTER-PASSIVE well.

FM ("Frequency Modulation") = Changing the transmitter frequency in exact

pace with speech or sound variations.
FREQUENCY SYNTHESIS = To "synthesize" anything is to create an

imitation or simulation from something else. The "basic" ways for generating
useful RF frequencies are a crystal oscillator or the L-C oscillator where the
frequency is determined by coil (L) and capacitor (C). However we can
process the output of an L-C oscillator through digital circuitry to simulate
many different, precise crystal-like frequencies, using only one crystal as a
reference standard. See also PLL, PHASE DETECTOR, VCO.

FSK = "Frequency Shift Keying." TRUE FSK actually moves the RF
frequency (transmitted and received) from one pre-determined point to
another, in contrast to "AFSK" (Audio Frequency Shift Keying") where the
transmitted signal remains steady and all shifting is done by audio tones.

GROUND-PLANE = ALL sections of a PC-board which are mechanically or
electrically connected to DC and RF ground. In the Ramsey FX design,
almost ALL of the top or upper side (component side) of the board is a
groundplane. The term is also used in antenna design: if your 2M or 1.25M
antenna has a vertical radiating element, plus four (or more) horizontal

FX-146 • 41

elements connected to RF ground, the horizontal elements are called a
"groundplane."

HIGH = In solid-state circuitry, to say a given device pin or circuit point is at a
"logic high" is to say that it shows a + DC supply voltage at that point.
Switching to the opposite state (LOW) or back again for some specific
purpose is a fundamental capability of the circuit.

HOUSE-NUMBER = A manufacturer's part number different from the
industry-standard description of a part. Example: LB3303HK (L1)

HYSTERESIS = the ability of an FM squelch circuit to remain open after
being broken by a weak signal which fluctuates further.

INPUT, INVERTING = see "Op Amp"
INPUT, NON-INVERTING = see "Op Amp"
I/O = acronym meaning "Input and Output" port or connection.
JUMPER = Short, plain wire, soldered to interconnect points in a circuit not

otherwise connected by board traces or other wiring.
KEY, "to key" = to turn on a transmitter's carrier signal momentarily, whether

by a telegraphy code key (the root of this very common radio jargon) or by a
push-to-talk switch.

L-C = A tuned circuit made of inductor (L) and capacitor (C).
LIMITER = The portion of an FM receiver circuit which chops off noise and

AM (amplitude modulation). It processes the IF signal so that only FM will be
detected.

LOCAL OSCILLATOR (LO) = An oscillator in a superhet receiver whose
output is mixed with another signal such as antenna input. See SUPERHET.

LOCK = The condition in a phased-locked-loop (PLL) in which all sections
are working together as intended and designed.

LOOP-FILTER = (See PLL). The output of a PLL phase detector is in the
form of pulses. The frequency of those pulses depends on the reference
frequency. The loop filter smooths out these pulses into a clean DC control
voltage for the VCO. (See: VCO)

LOW = A logic level at or near zero volts. (See HIGH).
MATRIX = A methodical criss-crossing of many connections.
MC- = Prefix for parts made by Motorola, Inc.
MIXER = A circuit section which gets two or more inputs and delivers a

single output. The output is equal to the sum of the input frequencies and
also to the difference between them.

MODULATION = See also: CW, FM. "Modulation" is simply the process of
imposing variations on a steady RF signal from an audio source such as
voice, music or data (see: AFSK).

MUTE = to turn off, to render silent. (See also SQUELCH)
N = can be any number to solve in a classroom problem, but "N" is THE

FX 146 • 42

magic number (decimal) to understand in FX binary frequency programming.
N = the frequency in KHz divided by 5 KHz.

NBFM = "Narrow-Band FM." NE- = prefix to transistors or IC's made by
Signetics, Inc.

OFFSET = The distance in KHz or MHz of the transmitted signal from the
primary or received signal. The "TX Offset" may be higher or lower,
depending on the repeater setup or other application.

OP-AMP = "Operational Amplifier," a high performance linear amplifier with
an Inverting input, a Non-inverting Input and one Output.

ORIENT, orientation = Yes, the Orient is Marco Polo's Far East where they
build many FM radios and where we buy many common parts. When we
ask you to "orient" a kit part one way or the other, we're just asking you to
get it RIGHT -- per all the "orientation" illustrations that we provide.

PACKET = Rapid transmission of intelligible computer generated data in
groups or bursts of a fixed length called "packets."

PHASE DETECTOR = In a frequency synthesizer, the phase detector
compares the signal from a reference oscillator to the signal from a
programmable counter and sends a corrected control voltage to the L-C
section of a VCO. Thus, it can be considered a phase "corrector." See also:
VCO, PLL, VARACTOR.

PLATED-THROUGH = Refers to a style of PC board manufacturing in which
traces on both sides of the board are interconnected by a coating of solder
around the inside of each hole.

POLARITY = Refers to the "+" and "-" sides of batteries, power supplies,
power cables, electrolytic capacitors, etc.

PLL = "Phase-Locked Loop," a frequency generator circuit in which an
oscillator output is analyzed by counters and a phase detector which
controls and corrects the voltage supplied to varactor diode(s) which
determine oscillator frequency.

POT = jargon for "potentiometer", a variable resistor, either a panel control
or a "mini" device on a PC-board.

PRESCALE, Prescaler = a circuit or device which divides an incoming
frequency down to a lower frequency so that it can be handled more easily
by later digital counting circuitry or devices.

PTT = "push to talk", referring to all switches and circuitry involved in turning
a transmitter on and off from a switch usually built into a microphone. This
switch may also be a relay or transistor in a packet TNC, etc.

PUFF = No, not the magic dragon. It's an easier way to say "picofarads" in
the Ramsey warehouse and other high tech temples.

QUADRATURE = Refers to the Phase Angle (90 degrees) considered by
the FM discriminator or detector.

REFERENCE FREQUENCY = a precise, known frequency, usually crystal-

FX-146 • 43

controlled, compared with another frequency, as is done in a PLL circuit.
See PHASE DETECTOR, PLL.

RSSI = "Received Signal Strength Indicator," a function of the MC13135 IC
and comparable circuits which permits MEASURING of the relative strength
of a received signal. A few microamps of variation can be interpreted as DB
(decibels) of signal strength.

RX = Abbreviation for receive, receiver, receiving. [See: TX]
SPEAKER-MIKE = speaker and microphone functions contain ed in the

same physical housing, as in the design of simple home intercoms. For ham
operators, this means that both speaker and microphone are in a
microphone casing with separate plugs from a common cord. Since such
accessories can use ANY style of plug for either mic or speaker function,
Ramsey Electronics has adopted the popular ICOM-compatible standard for
the FX transceivers.

SHIELD = The outer braid of audio or RF coaxial cable, or the aluminum
case enclosing a coil or transformer.The meta l case of a transceiver also
performs an important RF shielding function.The shield blocks or protects a
coil from the effect of nearby objects that would change its inductance. The
shielding on cable prevents the inner wire from radiating (RF) or from picking
up stray radiation such as AC hum.

SQUELCH = means literally, to subdue utterly or crushingly! In radio
communication, usually VHF and UHF, squelch is the circuitry needed to
subdue (mute) the background noise until a detected signal "breaks" the
squelch.

SUPERHET = A receiver design that converts the incoming desired
frequency to a lower Intermediate Frequency (IF) where most of the gain
and bandpass characteristics reside.

TOROID = A style of making coils or inductors where the insulated wire is
threaded ("wound") around a metallic form shaped like a doughnut. This
style of coil making generally eliminates any need for additional shielding
which may be needed to make the coil's inductance immune to the presence
of other nearby components or objects with metallic content.

TRIMMER = either a capacitor or resistor, miniature and variable, intended
to permit exact, final adjustment of circuit values.

TX = Abbreviation for transmit, transmitter, transmitting.
T-R = Abbreviation for "Transmit-Receive Switching", which can be

accomplished by manual switches, relays or solid-state devices such as the
PIN diodes used in the FX transceivers.

UNLOCK, unlocked = refers to the condition in a PLL (phased locked loop)
where one or more elements of the loop become defective or incorrect,
preventing the phase detector from supplying the correct control voltage to
the oscillator for the intended frequency of operation.

VARACTOR = a diode whose capacitance can be varied in step by the

FX 146 • 44

amount of DC voltage applied to it. The higher the voltage, the lower the
capacitance. See also VCO.

VCO = "Voltage Controlled Oscillator," an oscillator whose frequency is
varied by DC voltage applied to varactor diodes, which change capacitance
in step with the voltage level.

ZENER DIODE = a diode designed to have a very specific reverse
breakdown voltage. This property makes the Zener diode ideal for simple
voltage regulators or precise voltage drop elements.

FX-146 • 45

FX- TROUBLESHOOTING GUIDE

The FX- transceiver is designed to W-O-R-K with a minimum of adjustment
or alignment. By imprinting the location and correct orientation of each
component on the PC-board itself in addition to publishing detailed assembly
steps, we have virtually guaranteed the successful operation of your
transceiver from the moment you turn on the switch.

A detailed guide to servicing a transceiver requiring so few internal
adjustments is virtually pointless to compile. (It would be like writing a
troubleshooting guide to a jigsaw puzzle: "Make sure all puzzle parts are in
the right place, and it will be a nice, complete puzzle. That's it!")

The best assurance of trouble-free operation is to build, understand and test
your transceiver in the stage-by-stage sequence presented in this book. If
you chose to install all parts first and then test, and then encountered
difficulty, we recommend that you compare your assembly work to the stage­by-stage steps: USE the double-check spaces.

We simply MUST accept that any malfunction is caused by:

• incorrect part selection

• incorrect part orientation (diode or capacitor polarity, transistors,

IC's etc.)

• soldering error (missing connection, solder bridge)

• omitted part

• part damaged during assembly

• part defective in manufacturing (extremely rare)

• part damaged by incorrect installation of other part(s)

• part breakdown after extended operation

• defective external device or cable connected to the transceiver

circuit board.

The above possibilities may seem vague, but they cover what can go wrong
in any multi-stage electronic device. For this reason, it is important for you to
LEARN the FX circuit design in as much detail as possible, which is why
both the schematic and assembly instructions are presented stage by stage.

Troubleshooting is a process that considers EVERYTHING possible,
ESPECIALLY including every external device connected to the unit:

• power supply

• ALL cables and connectors

• microphone, speaker

• antenna AND

• ALL cables and connectors!

If you are at all hazy about the binary programming of the "N" number,

FX 146 • 46

despite the detail of our explanations, be sure you set one channel up for

146.52 MHz Simplex before you pursue troubleshooting. It is very important
to have a clear understanding of how to program the frequency synthesizer
and offset matrixes of your transceiver.

It's fairly easy to double-check "obvious" details such as IC orientation, diode
polarity, electrolytic capacitor polarity, and those other construction
essentials that we stress repeatedly. SOME of the more subtle assembly
errors which take very careful checking to find include the following:

 Any use of 2N3904 where VHF 2SC2498 is required
 Use of NPN where PNP is required: Q12,Q13,Q14
 Mistaken use of .01 or .001 disc capacitors where a small picofarad

value is specified.

 Major error in selecting resistors with similar color codes, like 100 ohm

(brown-black-brown) used for 100K (brown-black-yellow), or vice-versa.

 Reversal of the 8V and 5V voltage regulators
 L16, L14 or L13 touching the top groundplane.
 A single IC pin or IC socket pin bent under the plastic body of the device.

Simple operational tests are discussed at the end of most of the assembly
stages. Use these as a guide for tracing the circuit. If you make the effort to
understand each of the small sections of the big picture, you should have no
trouble in identifying the source of your problem.

If tracing and repairing complex circuits is new to you, we urge you to retrace
your assembly steps thoroughly. Take the extra time to really understand
circuit functions that might have been hazy during the excitement of
construction. Use basic LOGIC to narrow down the problem to a specific
stage.

If you ask a more experienced ham friend to look at your unit, it is up to you
to be able to recognize whether this person has the know-how and proper
equipment and tools to be of real help to you. Most hams really WANT to be
helpful, but good intentions are no substitute for competence. (If your friend
drags out the trusty soldering gun and big, rusty alligator clips, suggest a
fishing trip or antenna-fixing party instead!)

The best favor any friend can do for your kit project is to review the
correctness of part choices.

Factory Service is, of course, available at prevailing shop rates. The hams at
Ramsey enjoy providing kits to hams and hobbyists in addition to our Test
and Measurement Division work, and we're sure that you understand that
our company is not a ham club, and that our professional technicians aren't

FX-146 • 47

NOTE ON REPLACEMENT PARTS:

If you lose or damage parts during assembly or testing, you may, of course,
order any needed replacement parts by writing or faxing the Ramsey
Electronics, Inc. factory. Some of the more common parts may also be
picked up at Radio Shack or other local parts distributors. Use EXACT
values when replacing parts. Following is a GENERAL guide to obtaining
parts for your transceiver as quickly as possible:

A Radio Shack or local electronic parts distributor:
Resistors, electrolytic capacitors, disc capacitors, common NPN or
PNP transistors, Zener diodes, switching diodes, voltage regulator
(5V), hookup wire, LED, controls, antenna connector, replacement
1-amp fuses.

B Order from RAMSEY ELECTRONICS:

Most RF and VHF transistors, coils, crystals, PIN diod es, varactor
diodes, trimmers, filters and most IC chips.

C U1 and U6 are Motorola devices
These parts might be in stock at service shops featuring Motorola
equipment. There are acceptable "standard replacements" for some
of the semiconductors used in the transceiver. "SK" and "ECG"
standard replacements are stocked by local electronics parts
distributors or may be ordered through a Radio Shack store. The
following chart should help you make the most cost-effective choice
if replacement semiconductors are needed:

Part ID Type Recommended source RE=Ramsey,

RS=Radio Shack

Q1, etc. 2N3904 RS 276-1617

Q12,13,14 PNP 228256 RS276-1604 or 2N3906

Q2, etc. 2SC2498 ECG10, SK9139, 2N5179, or RE

Q3 NE02137 MRF901 or RE
Q9 2N3866 ECG311, SK3195 or RE
Q8 SD1127 MRF237, ECG341, SK9617 or RE

Signal diodes 1N4148 1N914, RS276-1620 (pack of 50)

D3,D23 BB405 RE

D2,D7 BA482 ECG553 or RE

D6 BA389 RE

D18 1N4002 RS276-1102, 1N4003

FX 146 • 48

D11,D12 6.2 V Zener RS276-561

VR1 7808 ECG964, SK3630 or RE
VR2 7805 RS276-1770

U1 MC13135 RE or Motorola
U2 LM380 ECG740A, SK3328 or RE
U3 MC12017 RE or Motorola
U4 LM324 RS276-1711
U5 LM358 ECG928, SK3691 or RE
U6 MC145152 RE or Motorola

FX-146 MASTER COMPONENT INDEX

The following pages were prepared to serve these purposes:

1. A general cross-reference for circuit study and servicing;

2. Additional help for parts sorting and identification;

3. An accommodation for experienced builders who prefer to work out their
own assembly sequences. (If you have ANY questions or doubt about a
part, refer to the specified assembly steps and the schematic diagram.)

Key to Component Index format:
A. Part designator number (e.g., C1, Q12, Y2, etc.)
B. Experienced builders always double-check!
C. Part value or manufacturer identification
D. Assembly step number (which also identifies general circuit stage per the

schematic.)

E. Component function note (or space for your own note.)
Key to assembly step letter-number codes:
The letter code indicates the circuit stage(s) in the step-by-step assembly

instructions. The numeral designates the specific step. If you have any
question whatsoever about a particular part, please consult its assembly step.

A: DC Power input
B: Receiver audio amplifier
CR: Receiver FM detector and squelch
DR: Antenna input, T-R switching, filters, RF preamplifiers
EF: VCO (Voltage Controlled Oscillator)

FX-146 • 49

G: PLL Frequency Synthesizer
H: Diode Matrix, Frequency Programming
M: Microphone Amplifier and PTT
TC: Transmit Coil and RF Choke Preparation
TX: Transmit Buffer, Driver and RF Final

PART VALUE or ID STEP NOTE:
[ ] [ ] C1 .001 A16

[ ] [ ] C2 .001 A13
[ ] [ ] C3 .001 A14
[ ] [ ] C4 .001 A15
[ ] [ ] C5 .01 CR9
[ ] [ ] C6 .1 CR15
[ ] [ ] C7 4.7 or 10 uF CR16
[ ] [ ] C8 .1 CR11
[ ] [ ] C9 4.7 or 10 uF CR10
[ ] [ ] C10 .001 CR19
[ ] [ ] C11 .1 CR17
[ ] [ ] C12 47 pF CR21
[ ] [ ] C13 .1 CR12
[ ] [ ] C14 27 pF CR13
[ ] [ ] C15 120 pF CR20
[ ] [ ] C16 .01 uF CR8
[ ] [ ] C17 100 pF DR28
[ ] [ ] C19 56 pF TX38
[ ] [ ] C20 100 pF DR16
[ ] [ ] C21 10 pF F8
[ ] [ ] C22 100 pF DR24
[ ] [ ] C23 .001 M5

FX 146 • 50

[ ] [ ] C24 .001 M16
[ ] [ ] C25 100 pF DR6
[ ] [ ] C26 .01 CR14
[ ] [ ] C27 8.2 pf DR8
[ ] [ ] C28 47 pf DR19
[ ] [ ] C29 330 uF electrolytic B7
[ ] [ ] C30 47 pf DR17
[ ] [ ] C31 47 pf DR22
[ ] [ ] C32 100 pf F13
[ ] [ ] C33 .01 B4
[ ] [ ] C34 470 uF B6
[ ] [ ] C35 100 pf F18 Couples VCO output to U1

[ ] [ ] C36 .01 E12
[ ] [ ] C37 .01 B8
[ ] [ ] C38 .001 F11
[ ] [ ] C39 .001 E14
[ ] [ ] C40 47 uF elec. E13a VCO +DC filter with Q4

[ ] [ ] C41 .1 B5
[ ] [ ] C42 1500 uf elec. A5 DC input filtering

[ ] [ ] C43 .001 E2
[ ] [ ] C44 .001 TX8
[ ] [ ] C45 100 pf F1
[ ] [ ] C46 100 pf F9
[ ] [ ] C47 100 pf DR4 RF coupling: antenna to RX

[ ] [ ] C48 4.7 or 10 uf B2
[ ] [ ] C49 100 pf F1
[ ] [ ] C50 100 pf F10
[ ] [ ] C51 22 pf E4
[ ] [ ] C52 .001 F3

FX-146 • 51

[ ] [ ] C53 .01 D10
[ ] [ ] C54 56 pf E3
[ ] [ ] C55 .01 TX30
[ ] [ ] C56 10 pf TX5
[ ] [ ] C57 .001 F12
[ ] [ ] C58 .1 uf TX26
[ ] [ ] C59 .001 TX27
[ ] [ ] C60 220 uf elec. TX25
[ ] [ ] C61 .001 TX17
[ ] [ ] C62 .001 M37
[ ] [ ] C63 .01 TX43 Low pass filter board

[ ] [ ] C64 .001 TX33
[ ] [ ] C65 .1 uf A17
[ ] [ ] C66 3.9 pf TX18
[ ] [ ] C67 2.2 uf elec. G11 PLL loop filter network

[ ] [ ] C68 .01 G23
[ ] [ ] C69 .01 G22
[ ] [ ] C70 2.2 uf elec. G10 PLL loop filter network

[ ] [ ] C71 39 pf TX37 Low pass filter board
[ ] [ ] C72 39 pf TX39 Low pass filter board
[ ] [ ] C73 18 pf TX29

[ ] [ ] C74 35 pf trimmer TX31 TX driver output tuning
[ ] [ ] C75 100 pf SMT chip TX3 See base of Q8
[ ] [ ] C76 15 pf TX9

[ ] [ ] C77 .001 M4
[ ] [ ] C78 22 pf TX20
[ ] [ ] C79 3.9 pf TX19
[ ] [ ] C80 39 pf G5
[ ] [ ] C81 35 pf trimmer G7 PLL ref freq adjust (see Y2)

FX 146 • 52

[ ] [ ] C82 10 pf TX10
[ ] [ ] C83 .001 M2
[ ] [ ] C84 35 pf trimmer TX32 TX final output tuning

[ ] [ ] C85 .1 uf G38 PLL loop filter
[ ] [ ] C86 .001 M1

[ ] [ ] C87 39 pf G4
[ ] [ ] C88 .001 M3
[ ] [ ] C89 .001 M15
[ ] [ ] C90 2.2 uf elec. G13 PLL loop filter

[ ] [ ] C91 .01 G24
[ ] [ ] C92 2.2 uf elec. G14 PLL loop filter

[ ] [ ] C93 4.7 or 10 uf elec. M14
[ ] [ ] C94 3.9pf F19
[ ] [ ] C95 4.7 or 10 uf elec. A6
[ ] [ ] C96 4.7 or 10 uf elec. G12
[ ] [ ] C97 .01 TX14
[ ] [ ] C98 .01 G25
[ ] [ ] C99 .01 E17
[ ] [ ] C100 4.7 or 10 uf elec. A11
[ ] [ ] C101 4.7 or 10 uf elec. CR24
[ ] [ ] C104 8.2 pf DR23

D: DIODES (All Types)

[ ] [ ] D1 1N914 or 1N4148 E15 Shunts D3 with C39 in receive
[ ] [ ] D2 BA482 PIN M34a Grounds RX RF input in transmit
[ ] [ ] D3 BB505 varactor E11 VCO L-C circuit with D23
[ ] [ ] D4 1N914 or 1N4148 DR9 Turns on D6 during receive
[ ] [ ] D5 1N914 or 1N4148 M38 Switches in R31 at high VCO freq
[ ] [ ] D6 BA479 PIN DR1 See T-R switch theory

FX-146 • 53

[ ] [ ] D7 BA482 PIN M34b See T-R switch theory
[ ] [ ] D8 1N914 or 1N4148 G34 works with D10,C85: see PLL theory
[ ] [ ] D9 1N914 or 1N4148 A18
[ ] [ ] D10 1N914 or 1N4148 G35 see D8
[ ] [ ] D11 1N914 or 1N4148 M31 assures positive switching by U4D
[ ] [ ] D12 1N914 or 1N4148 M32 " " " U4C
[ ] [ ] D13 1N914 or 1N4148 H8a disables -RPT during receive
[ ] [ ] D14 1N914 or 1N4148 H8b turns on Q15 during receive
[ ] [ ] D15 1N914 or 1N4148 H7 disables +RPT during receive
[ ] [ ] D16 1N914 or 1N4148 H9 turns off offsets during Simplex
[ ] [ ] D17 LED M42 transmit indicator
[ ] [ ] D18 1N4002 A7
[ ] [ ] D19 1N914 or 1N4148 H6 disables AUX offset for receive
[ ] [ ] D20 6.2 volt Zener diode CR32
[ ] [ ] D21 not used
[ ] [ ] D22 1N914 or 1N4148 M36
[ ] [ ] D23 BB505 varactor E10 VCO L-C tuning
[ ] [ ] D24 1N914 or 1N4148 G36
[ ] [ ] D26 1N914 or 1N4148 TX36
[ ] [ ] D25-DX 1N914 or 1N4148 Stage H Synthesizer Programming

FL: FILTERS

[ ] [ ] FL1 21.4 MHz. crystal CR30 Receiver 1st IF
[ ] [ ] FL2 455 KHz. ceramic CR18 Receiver 2nd IF

J: JACKS

[ ] [ ] J1 5-pin DIN A12 Packet I/O
[ ] [ ] J2 miniature 3.5mm. B15 Speaker connection
[ ] [ ] J3 SO-239 TX45 Antenna
[ ] [ ] J4 subminiature 2.5mm. M43 Microphone

FX 146 • 54

L: INDUCTORS (Coils, Transformers, Chokes):

[ ] [ ] L1 455 KHz

LB53303HK

[ ] [ ] L2 .015 uH DR20 Q2 input bandpass filter
[ ] [ ] L3 not used
[ ] [ ] L4 not used
[ ] [ ] L5 .015 uH DR18
[ ] [ ] L6 .015 uH DR21
[ ] [ ] L7 variable coil E1 VCO tank circuit with D3,D23
[ ] [ ] L8 2.2 uH TX34
[ ] [ ] L9 VK200 RF choke TX49 Install AFTER alignment!
[ ] [ ] L10 .04 uH TX47 Install AFTER alignment!
[ ] [ ] L11 .33 uH, mini TX7
[ ] [ ] L12 2.5 T TX40
[ ] [ ] L13 1.5T, 5/16" dia. TX28
[ ] [ ] L14 .015 uH TX24
[ ] [ ] L15 2.5T, 5/16" dia. TX21
[ ] [ ] L16 2.5T, 5/16" dia. TX16
[ ] [ ] L17 2.2 uH DR2
[ ] [ ] L18 .33 uH axial TX22
[ ] [ ] L19 VK200 RF choke TX15 See stage "TC" for winding

CR23 FM quadrature adjust

[ ] [ ] L20 500 uH choke A4 Ignition hash filter
[ ] [ ] L21 .33 uH mini F17
[ ] [ ] L22 2.5T TX41
[ ] [ ] T1 6T/2T toroid CR34 VCO injection to U1

Q: TRANSISTORS (All Types):

[ ] [ ] Q2 2SC2498 NPN RF DR27 Receiver RF preamp #2
[ ] [ ] Q3 NE021 NPN RF DR12 Receiver RF preamp #1
[ ] [ ] Q4 2N3904 NPN E19 VCO DC input filter

FX-146 • 55

[ ] [ ] Q5 2SC2498 NPN RF F8 VCO common base buffer
[ ] [ ] Q6 2N3904 NPN B9 Carrier detect switch
[ ] [ ] Q7 2SC2498 NPN RF E9 VCO
[ ] [ ] Q8 SD1127 or MRF237 TX2 Transmit final amplifier
[ ] [ ] Q9 2N3866 NPN RF TX1 Transmit driver
[ ] [ ] Q10 NE021 TX14 Transmit buffer
[ ] [ ] Q11 2N3904 M18 Grounds mic amp in receive
[ ] [ ] Q12 PNP 2N3906

(228256)

[ ] [ ] Q13 PNP 2N3906

(228256)

[ ] [ ] Q14 PNP 2N3906

(228256)

[ ] [ ] Q15 2N3904 H10 Offset matrix switching
[ ] [ ] Q16 2SC2498 F15 VCO buffer
[ ] [ ] Q17 2N3904 CR33 Voltage regulator

M20 PTT switching

M21 +8R PTT output

M22 +8T PTT output

R: RESISTORS (Fixed, Trimmers, and Panel-Mounted)

[ ] [ ] R1 220K CR29
[ ] [ ] R2 1K CR27
[ ] [ ] R4 68K CR4
[ ] [ ] R5 10K CR3
[ ] [ ] R6 3.3K CR25 Sets hysteresis for U1
[ ] [ ] R7 100K pot w/switch A2,B12 Volume
[ ] [ ] R8 47 ohm CR26
[ ] [ ] R9 270 CR6
[ ] [ ] R10 470 DR26
[ ] [ ] R11 47K CR2
[ ] [ ] R12 100 DR15
[ ] [ ] R13 100K pot CR31 Squelch control
[ ] [ ] R14 47K DR25
[ ] [ ] R15 1K E16

FX 146 • 56

[ ] [ ] R16 47K DR13
[ ] [ ] R17 470 ohm DR14
[ ] [ ] R18 270 ohm E7
[ ] [ ] R19 10K E13b
[ ] [ ] R20 270 F5
[ ] [ ] R21 470 M33
[ ] [ ] R22 10K E6
[ ] [ ] R23 100 ohm F6
[ ] [ ] R24 10K CR5
[ ] [ ] R25 47K E18
[ ] [ ] R26 51 ohm F3
[ ] [ ] R27 47K F4
[ ] [ ] R28 470 ohm DR5
[ ] [ ] R29 100 ohm TX6
[ ] [ ] R30 51 ohm E5
[ ] [ ] R31 47K M39
[ ] [ ] R32 82 (1/2W) TX48
[ ] [ ] R33 47K M40
[ ] [ ] R34 270 ohm TX13
[ ] [ ] R35 100K E20
[ ] [ ] R36 10K TX11
[ ] [ ] R37 100K M13
[ ] [ ] R38 10K G6
[ ] [ ] R39 47K M30
[ ] [ ] R40 100K M26
[ ] [ ] R41 not used
[ ] [ ] R42 2.2K A20

FX-146 • 57

[ ] [ ] R43 10K G26
[ ] [ ] R44 22K G20
[ ] [ ] R45 82 ohm 1/2W TX23
[ ] [ ] R46 10K trimpot M19
[ ] [ ] R47 10K G31
[ ] [ ] R48 10K G33
[ ] [ ] R49 10K M9b
[ ] [ ] R50 10K M9a
[ ] [ ] R51 47K M10
[ ] [ ] R52 10K G27
[ ] [ ] R53 22K G21
[ ] [ ] R54 200 or 220 (1/2W) DR3
[ ] [ ] R55 10K G19
[ ] [ ] R56 47K M11
[ ] [ ] R57 2.2K M6
[ ] [ ] R58 270 ohm M8
[ ] [ ] R59 100K M7
[ ] [ ] R60 10K M23
[ ] [ ] R61 2.2K M12
[ ] [ ] R62 10K M24
[ ] [ ] R63 470 ohm M27
[ ] [ ] R64 470 ohm M28
[ ] [ ] R65 1K H4
[ ] [ ] R66 47K E8
[ ] [ ] R67 10K H5
[ ] [ ] R68 1K H1
[ ] [ ] R69 1K H2
[ ] [ ] R70 1K M41

FX 146 • 58

[ ] [ ] R71 100K H22-H40 U6 counter input pulldowns
[ ] [ ] R72 " " "
[ ] [ ] R73 " " "
[ ] [ ] R74 “ “ “
[ ] [ ] R77 " " "
[ ] [ ] R78 " " "
[ ] [ ] R79 " " "
[ ] [ ] R80 " " "
[ ] [ ] R81 " " "
[ ] [ ] R82 " " "
[ ] [ ] R83 " " "
[ ] [ ] R84 " " "
[ ] [ ] R85 " " "
[ ] [ ] R86 " " "
[ ] [ ] R87 " " "
[ ] [ ] R88 " " "
[ ] [ ] R89 " " "
[ ] [ ] R90 10K G30
[ ] [ ] R91 100K H11-H21 U6 counter input pulldowns
[ ] [ ] R92 " " "
[ ] [ ] R93 " " "
[ ] [ ] R94 " " "
[ ] [ ] R95 " " "
[ ] [ ] R96 " " "
[ ] [ ] R97 " " "
[ ] [ ] R98 " " "
[ ] [ ] R99 " " "
[ ] [ ] R100 100K H11-H21 U6 counter input pulldowns
[ ] [ ] R101 " " "
[ ] [ ] R102 10K G32

FX-146 • 59

[ ] [ ] R103 47K G28
[ ] [ ] R104 10K G29

[ ] [ ] R105 100 ohm F16
[ ] [ ] R106 10K F15
[ ] [ ] R107 10K M35
[ ] [ ] R108 2 ohm B3
[ ] [ ] R109 47K B10
[ ] [ ] R110 10K TX12
[ ] [ ] R111 4.7K M25
[ ] [ ] R112 4.7K M29
[ ] [ ] R114 1K H3
[ ] [ ] R115 1K TX42
[ ] [ ] R116 100K H11-21
[ ] [ ] R117 100K “
[ ] [ ] R118 100K “
[ ] [ ] R119 270 ohm CR36
[ ] [ ] R119A 1K TX35

V: VOLTAGE REGULATORS

[ ] [ ] VR1 7808 A9 +8VDC where needed
[ ] [ ] VR2 7805 A10 +5VDC where needed

Y: CRYSTALS

[ ] [ ] Y1 21.855 MHz CR23 Receiv er IF oscillator
[ ] [ ] Y2 10.240 MHz G3 PLL reference oscillator

FX 146 • 60

S: SWITCHES TP: TEST POINTS

[ ] [ ] S1 on R7 (volume) A2 DC on-off
[ ] [ ] S2 12 position "H" Frequency selection
[ ] [ ] TP1
[ ] [ ] TP2
[ ] [ ] TP3

F20 VCO control voltage
F20 VCO output frequency
F20 U3 prescaler output

U: INTEGRATED CIRCUITS

[ ] [ ] U1 MC13135 CR1 FM dual-conversion receiver
[ ] [ ] U2 LM380 B1 Receiver audio amplifier
[ ] [ ] U3 MC12017 F21 Dual- modulus 64/65 prescaler
[ ] [ ] U4 LM324 M17 Quad op amp: mic and PTT
[ ] [ ] U5 LM358 G9 Dual op amp: see PLL theory
[ ] [ ] U6 MC145152 G2 PLL Frequency Synthesizer
[ ] [ ] U7 74HC283 G15 4-bit high speed binary Adder
[ ] [ ] U8 74HC283 G16 " "
[ ] [ ] U9 74HC283 G17 " "
[ ] [ ] U10 74HC283 G18 " "

FX-146 • 61

The RAMSEY FX Transceiver Kit WARRANTY

Please read carefully BEFORE calling or writing in about your Kit. Most problems can be
solved WITHOUT contacting the Factory!

Notice that this is not a "fine print" warranty. We want you to understand your rights and ours
too! All Ramsey kits will work if assembled properly. The very fact that your kit includes this
manual is your assurance that a team of knowledgeable people have field-tested several
"copies" of this kit straight from the Ramsey inventory. If you need help, please read through the
manual carefully: all information required to properly build and test your kit is contained within its
pages! In particular, the FX Transceiver has been documented exhaustively.

1. DEFECTIVE PARTS: It's always easiest to blame a part for a problem in your kit. Before you conclude that
a part may be bad, thoroughly check your work. Today's semiconductors and passive components have
reached incredibly high reliability levels, and it's sad to say that our human construction skills have not. Very
rarely, a sour component might slip through. All our kit parts carry the Ramsey Electronics Warranty that they
are free from defects for a full (90) days from the date of purchase. Defective parts will be replaced at our
expense. If you suspect a part to be defective, please mail it to our factory for testing and replacement.
Please send only the defective part(s), NOT the entire kit. The part(s) MUST be returned to us in suitable
condition for testing. Please be aware that testing can usually determine if the part was truely defective or
damaged by assembly or usage. Don't be afraid to tell us that you "blew it". We're all human: in most cases,
replacement parts are very reasonably priced.

2. MISSING PARTS: Ramsey Electronics project kits are packed with pride in the U.S.A. If you believe we
packed an incorrect part or omitted a part clearly indicated in your assembly manual as supplied with the
basic kit by Ramsey, please write us with information on the part you need and proof of the kit purchase.
Before assuming a part value is incorrect, check the parts list carefully to see if it is a critical value such as a
specific coil or IC, or whether a range of values is suitable (such as 100 to 500 ufd.). Often, common sense
will solve a mysterious missing part problem. If you are missing five 10K ohm resistors and find five extra 1K
resistors, a simple VOM check will likely confirm that the "1K" resistors are actually the "missing" 10K units.
("Hmmm, I guess the red band really does look orange!")

3. FACTORY REPAIR OF ASSEMBLED KITS: To qualify for Ramsey Electronics factory repair, kits MUST:

1. NOT be assembled with acid core solder or flux.

2. NOT be modified in any manner.

3. BE returned in fully assembled form, not partially assembled.

4. BE accompained by payment of the proper repair fee. No repair will be begun until we
have received the MINIMUM repair fee of $49.00, or authorization to charge it to your

INCLUDE a description of the problem and legible return address. Do not send a separate letter: include all
correspondence with the unit. Please do not include your own hardware such as non-Ramsey cabinets,
knobs, cables, external battery packs, and the like. Ramsey Electronics reserves the right to refuse to repair
ANY item in which we find excessive problems or damage due to construction methods. To assist customers
in such situations, Ramsey Electronics, Inc. reserves the right to solve their needs on a case-by-case basis
without creating policy or precedent.

Please understand that our technicians are not volunteers and that set-up, testing, diagnosis, repair and
paper work can easily take over two hours of paid employee time on even a simple problem. Understand
too, that aligment is part of the kit building process and is not covered by this Warranty. Of course, it
we find that a part was defective in original manufacture, there will be no charge to repair your kit (But please
realize that our technicians know the difference between a defective part and parts burned out or damaged
through improper use or assembly.)

4. REFUNDS: You are given ten (10) days to examine our products. If you are not satisfied, you may return
your unassembled kit with all parts and instructions and proof of purchase to the factory for a full refund. The
returned package should be packed securely. Insurance is recommended. Please do not cause needless
delays, read all information carefully.

RAMSEY ELECTRONICS, INC. 793 Canning Parkway, Victor, New York 14564

credit card account.

Telephone [phone] Fax [phone]

FX 146 • 62

KIT ASSEMBLY PHASE 1:

Stage A: DC Power Regulation & Distribution
Plus Packet Data I/O Connector

Stage B: Receiver Audio Amplifier
Stage CR: Integrated Circuit FM Receiver
Stage DR: Receiver, Tuned RF Input and Preamp
Stage E-F: Transceiver VCO with Buffer Stages

Each set of Assembly Instructions is introduced by an explanation of how
that part of the circuit works and what it is for. LEARN as you build!

ALSO INCLUDED IN THIS SECTION:

Master Kit Parts List
Important Information About Kit Parts and the Printed Circuit Board.

TOOLS AND EQUIPMENT REQUIRED FOR CONSTRUCTION, PLL
SYNTHESIZER ALIGNMENT, & TRANSMITTER ADJUSTMENT

 Medium-heat (25 to 50 watt) soldering pencil with clean, tinned

tip

 Damp sponge to keep soldering tip clean
 Thin diameter ROSIN core solder
 Diagonal cutters or wire nippers
 Wire strippers
 Small pair of pliers
 Small screwdriver
 Ruler
 Tweezers (to install SMT C75)
 Non-metallic alignment tool
 Digital Voltmeter (DVM)
 50-ohm Dummy Load (5-10 watt rating)
 VHF RF power output meter

ALIGNMENT: A feature of the FX design is that Synthesizer Alignment can
be accomplished by listening carefully to a transmitted signal of known
accuracy. To adjust trimmer capacitor C81 "by the numbers," use your
Ramsey Frequency Counter or a digitally accurate VHF receiver with BFO.

FX-146 • 63

FX-146 Transceiver Assembly Phase 1: Circuit stages A through E-F
FX-146 MASTER PARTS LIST

Before beginning assembly, take some time to check and organize these kit
components in such a way that you can find them easily and not lose any or
confuse them. Leave parts supplied on tape strips in the strips until you need
them. The following headings also provide logical sorting categories. Popular
methods for organizing parts include egg cartons, muffin tins, corrugated
cardboard edges, or pressing the leads into a block of styrofoam.

INTEGRATED CIRCUITS

 1 MC13135 24-pin DIP FM Receiver IC (U1)
 1 LM380 14-pin DIP Audio Amplifier IC (U2) [Do NOT use socket]
 1 12017 8-pin DIP divide-by 64/65 Prescaler (U3)
 1 LM324 14-pin DIP Quad Op-amp IC (U4)
 1 LM358 8-pin DIP Dual Op-amp IC (U5)
 1 MC145152 28-pin DIP PLL Synthesizer IC (U6)
 4 74HC283 16-pin high speed 4-bit Binary Adder (U7,U8,U9,U10)
 1 7808 8V voltage regulator [VR1]
 1 7805 5V voltage regulator [VR2]

TRANSISTORS:

 5 NPN transistor, type 2N3904 or equivalent (Q4,6,11,15,17)
 3 PNP transistor, 2N3906-type [marked 228256] (Q12,13,14)
 2 NPN VHF type NE02137 (Q3,10) [flat disc type marked '021']
 4 NPN VHF type 2SC2498 or 2570 (Q2,7,5,16)(Sort these carefully

from the 5 type 2N3904 for Q1, etc.)

 1 RF NPN type 2N3866 (transmit driver, Q9)
 1 RF NPN type MRF237 or SD1127 (transmit final, Q8)

DIODES (Note color code descriptions CAREFULLY!):

 1 LED (D17, transmit indicator)
 100+ 1N914 or 1N4148 switching diode

(D1,4,5,8,9,10,11,12,13,14,15,16,19,22,24,26,plus PLL matrix)

 2 Varactor diode, type BB505 (D3, D23) [orange labeled BB505]
 1 PIN diode, type BA479 (D6)
 2 PIN diode, type BA482 (D2, D7) [orange body, red band]
 1 1N4002 rectifier diode (D18) [largest black body, gold band]
 1 6.2 volt zener diode (D20) [gray body with black band]

FX 146 • 64

CRYSTALS:

 1 10.240 MHz, has 2 leads (Y2, PLL reference frequency)
 1 21.855 MHz, has 2 leads (Y1, receiver IF oscillator)
 1 21.4 MHz crystal filter, has 3 leads (FL1, 1st IF filter)

INDUCTORS:

 1 455 KHz shielded inductor, marked LB53303HK (L1)
 1 Shielded variable coil, marked 8488 5-5 (L7)
 4 .015 uH, 1.5 turns, .125" diameter (L2,5,6,14)
 1 .04 uH, 4 turns, red color, (L10)
 1 500 uH noise suppression choke, large with black shrink tubing over

the body (L20)

 2 .33 uh., upright-style green molded mini-inductor: markings include 2

orange stripes (L11,L21)

 1 .33 uh., axial leads, wirewound with orange-orange-silver bands (L18)
 2 2.2 uh. axial leads, molded inductor, marked with two red, one gold

bands (L8,L17)

 1 tinned wire to make: 1.5 turn, .375" diameter, hand-wound (L13)
 4 tinned wire to make: 2.5 turn, .375" diameter, hand-wound

(L12,15,16,22)

 2 small size tinned wire and cores to make: RF chokes, hand-wound on

ferrite cores (L9,L19)

SPECIALIZED COMPONENTS:

 1 Ramsey FX-series main and low pass filter printed circuit boards
 2 ferrite cores (for making L9,L19)
 1 455 KHz ceramic filter, molded cube, 3 pins. (FL2)
 1 100 pf SMT chip capacitor (C75)

INTERNAL ALIGNMENT COMPONENTS:

 1 10K trimmer potentiometers, marked 103 (R46)
 3 35 pf trimmer capacitors (C74,C81,C84)

FIXED-VALUE CAPACITORS (RF-critical picofarad values):

 3 3.9 pf (C66,C79,C94)
 2 8.2 pf (C27,104)
 3 10 pf (C21,C56,C82)
 1 15 pf (C76)
 1 18 pf (C73)
 2 22 pf (C51,C78)
 1 27 pf (C14)
 4 39 pf (C71,C72,C80,C87)

FX-146 • 65

 4 47 pf (C12,28,30,C31)
 2 56 pf (C19,54)
 10 100 pf (may be marked 100 or 101)

(C17,20,22,25,32,35,45,46,47,50)

ADDITIONAL DISC CAPACITORS:
 22 .001 uf (may be marked .001, 102 or 1nf)

(C1,2,3,4,10,23,24,38,39,43,44,52,57,59,61,62,64,77,83,86,88,89)

 16 .01uf (may be marked .01, 103 or 10 nf)

(C5,15,16,26,33,36,37,53,55,63,68,69,91,97,98,99)

 8 .1 uf (may be marked .1 or 104) (C6,8,11,13,41,58,65,85)
ELECTROLYTIC (Polarized) CAPACITORS:

 4 2.2 uf electrolytic (C67,70,90,92)
 8 4.7 to 10 uf electrolytic (C7,9,48,93,95,96,100,101)
 1 47 uf electrolytic (C40)
 1 220 uf electrolytic (C60)
 1 330 uf electrolytic (C29)
 1 470 uf electrolytic (C34)
 1 1500 uf electrolytic (C42)

FIXED RESISTORS:

 1 2 ohms [red-black-gold] (R108)
 1 47 ohms [yellow-violet-black] (R8)
 2 51 ohms [green-brown-black] (R26,30)
 2 82 ohms, 1/2 watt, larger size, [gray-red-black] (R32,45)
 4 100 ohms [brown-black-brown] (R12,23,29,105)
 1 220 ohms, 1/2 watt [red-red-brown] (R54){This resistor may range

from 200 to 240 ohms.}

 6 270 ohms [red-violet-brown] (R9,18,20,34,58,119)
 6 470 ohms [yellow-violet-brown] (R10,17,21,28,63,64)
 9 1K ohms [brown-black-red] (R2,15,65,68,69,70,114,115,119a)
 3 2.2K ohms [red-red-red] (R42,57,61)
 1 3.3K ohms [orange-orange-red] (R6)
 2 4.7K ohms [yellow-violet-red] (R111,112)
 22 10K ohms [brown-black-orange] (R5,19,22,24,

36,38,43,47,48,49,50,52,55,60,62,67,90,102,104,106,107,110)

 2 22K ohms [red-red-orange] (R44,53)
 13 47K ohms [yellow-violet-orange]

(R11,14,16,25,27,31,33,39,51,56,66,103,109)

 1 68K ohms [blue-gray-orange] (R4)
 37 100K ohms [brown-black-yellow] (R35,37,40,59,71-89,91-

101,116,117,118)

 1 220K ohms [red-red-yellow] (R1)

FX 146 • 66

CONTROLS, HARDWARE AND MISC.:
 1 volume control potentiometer with switch (may be any value from 10K

to 100K) (R7,S1)

 1 10K squelch control potentiometer (R13)
 1 12-position rotary switch (S2)
 1 3.5 mm. Jack, miniature (J2, speaker)
 1 2.5 mm. Jack, subminiature (J4, microphone)
 1 5-pin female DIN PC-mount connector (J1, packet)
 1 SO-239 coaxial RF connector (J3)
 3 sets of: 4-40 screw and nut (to mount J3 and VR1)
 1 28 pin DIP IC socket (for U6)
 1 DC power cord with inline fuseholder and 1A fuse
 1 1/2" panel-mount strain relief for DC power cord
 1 length of No. 20 bus wire (to make diode matrix bridges)
 1 length of No. 24 bus wire (to make L9 and L19)
 1 hookup wire, as needed (may include 1,2, or 3 conductors)
 3 wire cable ties
 1 5/16"x18 bolt (to wind coils on for perfect spacing)
 1 document packet, including this manual

REQUIRED, NOT SUPPLIED WITH KIT:

 Thin-diameter rosin-core solder
 Correct tools for all phases of assembly (see text)
 Microphone and speaker per specifications in text (J2,J4 and PTT circuit

are designed for ICOM-type mike)

 Fused, 13.5 VDC power supply or battery
 50-ohm dummy load
 50-ohm 2-meter antenna with PL259 or adapter

OPTIONAL, RECOMMENDED:

 Ramsey FXC Transceiver Case and Knob Kit
 Ramsey speaker mike SM-7

IMPORTANT:
For proper RF shielding and secure mounting of controls, connect ors, and

the PC board, immediate consideration must be given to the transceiver
enclosure as an integral part of the assembly process. The FXC matching
case set is the quality, custom designed finishing touch for your transceiver.

FX-146 • 67

VERY IMPORTANT PC BOARD ASSEMBLY INFORMATION FOR A-L-L
OUR BUILDERS!

1. Your FX- transceiver PC board is double-clad with plated- through holes.
What this means in practice is that it is VERY important to select and
install correct part values the FIRST time around. This type of board
makes "desoldering" much more difficult and risky because the solder
adheres inside the hole and flows to the component side of the board as
well. It is VERY tricky to remove a part without damaging it. If too much
de-soldering heat or component "pulling" is used, there is also the
serious risk of damaging small PC board traces. Be careful and
methodical in assembly!!!

2. Do not, under any circumstances, install L9, R32 or L10 until instructed
to do so in Assembly Stage "TX." This applies even if you are following
your own assembly sequences. This procedure will prevent damage to
Q9 and Q8 during the initial test and alignment procedure.

3. Do not attempt to "re-engineer" our transistor orientation illustrations.
Simply point flat sides or tabs as illustrated.

4. After installing all parts, you will see a few empty holes in the circuit
traces on the top or component side of the board. These plated-through
holes are placed intentionally to connect with traces on the solder side.
The hole IS the connection! However, if these holes nag at you, simply
fill them in with a touch of solder -- AFTER verifying that all parts have
been placed and installed correctly.

5. Additional "empty" holes are marked on the PC board to allow for easy
connection of accessories or modifications as you begin to customize
your transceiver. See "GUIDE TO FX- CIRCUIT ACCESS POINTS."

6. The purpose of check boxes “” in the assembly steps is to make it
easy to check the accuracy of your work at the end of each step.

7. Almost all resistors are mounted in vertical (upright) position. You can
see that the wire leads for resistors come in several styles. If a resistor's
pre-trimmed lead is ever too short for upright installation, simply solder a
scrap wire nipped from another resistor to extend its length.

8. Some of the resistors and miniature inductors used in this project require
upright or vertical installation. It is important to follow the orientation
illustrated for vertically installed parts. Always put the body of the part in
the hole with the circle!

9. Whenever you have a choice, install parts with stamped markings so
that you can still see the markings later. This will help greatly with any
possible troubleshooting needed.

10. PARTS SORTING: In a kit of this size and complexity, there is no single
best way to sort and organize the 300+ individual components used. We

FX 146 • 68

at the factory have tried to help by grouping similar or related parts in
individual sealed bags. Sorting organizers popular among kit builders
include empty egg cartons, muffin tins, small box tops, or the corrugated
edges of box cartons. Since the assembly of this kit is presented in
distinct stages, some builders may prefer to group their parts by stage
before beginning assembly.

11. HELPFUL HINT: Many of the parts are supplied on tape strips cut from
bulk reels. Leave them taped, which keeps them nicely sorted for you. It
is NOT necessary to pull the entire lengths of both leads from the tape.
Simply nip the leads right at the edge of the tape, and you'll have plenty
of length to work with.

12. The .01 disc capacitors may be marked in any of the following ways: .01,
103 or 10n (nanofarads)

13. Similarly, .001 ufd. discs may be marked: .001, 102 or 1n(nanofarads)

14. The several .1 uf units required should be clearly recognizable and
often will have a rectangular rather than disc shape. Their markings
may be .1 or 104.

15. Small Picofarad values are clearly stamped on capacitor bodies. 100 pf.
units may be marked 100 or 101.

16. We tried to make it clear in both lists and assembly steps that some
components can have a RANGE of acceptable values, even though a
single value is indicated on the schematic, the control document for this
project. A rule of thumb is that a value within 10% of the stated value will
be fine: 2 or 2.2 pf, 4.7 or 5 pf, 200 or 220 ohm and so forth. 10 uf
electrolytics may be 4.7 to 10 uf. Remember that there's a reason for the
"tolerance" codes for all parts. Unless we scream in bold print that
something must be exact down to the last micro-henry, ohm or partial
picofarad, PLEASE assume the 10% rule in sorting through your kit
parts!

17. Manufacturer stamping patterns can vary, and we sometimes need to
use simple logic and deduction to identify parts, particularly the
extremely common ones. For example: if your kit includes 3 identical
transistors with no apparent body marking at all, you may presume them
to be the 3 PNP transistors described as 2N3906, 228256 or equivalent.

18. Check your manual or kit package for any insert page advising that a
part identification or physical description has changed. We cannot
control how manufacturers may vary their product codes or colors of
plastic.

19. Observe correct POLARITY when installing all diodes and electrolytic
capacitors!

20. Please review No. 1 above!

FX-146 • 69

21. Use the extra spaces provided throughout this manual to write down the
details of any changes or revisions noted on additional sheets that may
be supplied with your kit.

22. You will be installing various wires for switches, controls and jacks very
early in the assembly procedure. This is contrary to normal building or
manufacturing practice but will permit progressive testing of completed
stages. Follow the suggestion at the end of Stage CR for tying down
these wires for protection and your convenience during further assembly
work.

23. Examine your FX- circuit board. Notice that the side with silkscreened
parts outlines is covered almost completely by tinned copper or "foil."
This is called a groundplane. This side is the Top or COMPONENT
SIDE of the board. All parts (except SMT C75) will be mounted on this
side. The other side has most of the printed circuit traces and is called
the Bottom or CIRCUIT SIDE.

ABOUT THE WIRE SUPPLIED WITH YOUR KIT:
Your kit parts include lengths of wire for making all needed connections from

the PC board to the controls and jacks. Because there is nothing critical in
the functions of these wires, the color and style of wire lengths actually
packed in your kit may vary. You may receive lengths of 2 or 3 conductor
wire (such as speaker cable or ribbon cable) or a supply of simple si ngle
conductor hookup wire. Use the heavier gauge wire for the power supply
connections in the following steps, saving the lighter gauge wire for jacks
and controls. The bare wire is used for constructing the diode matrix for
frequency programming and for making a few coils and RF chokes. The
piece of thin, enameled "magnet" wire is to be wound on the small "toroid"
coil in Assembly Stage "CR."

"TINNING" is the process of heating the stripped end of a wire and LIGHTLY
flowing solder so that all strands are bonded together. This practice, while
not essential, generally makes for easier soldering and physically stronger
connections.BROKEN WIRES are the primary cause of malfunctions in ham
equipment and computers! Please follow our instructions in Stage CR
(PAGE 27) for securing completed cables to the PC board temporarily so
the connections will not get damaged during further assembly.

IMPORTANT NOTE REGARDING FLEXING WIRES: In Stages A, B, CR,
and M, you will install numerous wires from the PC board for panel controls
and jacks. Repeated flipping of the board during assembly can damage
these wires and also become very annoying during kit assembly. PLEASE
tie the wires down as noted on page 27, using one of the cable ties provided.

Take your time, learn about what you're doing and ENJOY your FM
Transceiver project!

FX 146 • 70

STAGE A: DC POWER INPUT REGULATION & DISTRIBUTION and
PACKET RADIO I/O CONNECTOR (J1)

The "power supply" for your FX- transceiver is, basically, any "12-volt"
battery or well designed power supply operating from 120VAC or other
source. In theory, all "12V" sources should provide pure DC voltage to your
FX- transceiver DC input. In fact, there are many variations and
imperfections in common "12VDC" sources, ranging from weak batteries,
poorly filtered AC powered supplies, vehicle ignition noise, or just badly
made power supplies.

Stage "A" of your FX- Transceiver is designed to help your radio survive
quite a wide variety of imperfections. It's not a "power supply" in itself, but it
comes close, because it performs all the essential functions expected from a
good solid-state DC source. Just add 12-15VDC from a battery, vehicle or
bench supply.

Much of the circuitry operates on the regulated 8 volts supplied by voltage
regulator VR1. If you have already looked around the schematic diagram
and also seen "+8R" or "+8T", these are points where the regulated 8V
output is switched for Receive or Transmit by the PTT (push to talk) circuitry
(Q12, U4c, U4d, Q13, Q14) which we'll discuss in more detail when it's time
to build it in Stage M.

The Receiver IC (U1) and the digital frequency synthesis circuit is powered
by +5 volts regulated by VR2. The op amps used in the circuit (U4 and U5)
operate from this single supply through the use of voltage divider networks
at the respective IC's. The full 12-15 volt input is supplied to the transmitter
RF output section and to the receiver audio amplifier (U2).

The large 1500 uf capacitor (C42) and inductor L20 are installed at the DC
input to filter out ignition noise, etc. Fuse F1 is contained in the power cord
and the DC power switch is integral to the volume control. The DC negative
(black) wire is soldered directly to the PC board ground plane.

The Packet Connector
The Packet I/O Jack (J1) is not a "stage" or section of your transceiver in

itself. It is simply a convenient "port," to use computer terminology, which
gives a packet TNC (terminal node controller) convenient access to the
microphone and receiver audio circuits. We'll install J1 and its associated
bypass capacitors at the beginning -- because now is as good a time as any,
and it gets some parts on your PC board quickly and easily! Also, having J1
in place will give a little extra protection to other parts when you are working
on the solder-side of the board.

FX-146 • 71

STAGE A: DC POWER INPUT REGULATION & DISTRIBUTION and
PACKET RADIO I/O CONNECTOR (J1)

FX 146 • 72

Stage A: ASSEMBLY STEPS

 A1. Strip 1/8" of insulation from the heavier-gauge black wire, insert and

solder in the GROUND hole. This connection may be soldered on the
TOP side of the board as well as the solder side.

 A2. Strip 1/8" of insulation from the in-line

fuse wire and solder it to one of the S1
switch lugs of the volume control (R7).
The switch lugs are the two outermost
lugs of the 5 lugs.

 A3. Strip 1/8" of insulation from each end

of the heaviest gauge 1 conductor wire
remaining in your kit. Solder one end to
the other switch lug on R7 and the other

VOLUME

IN
OUT

GND

FUSE

PWR

end to the PWR point on the PC board. MAKE SURE that ALL strands of
this wire are neatly inserted and soldered in the hole. Any stray strand
will cause a direct short when it touches the ground plane.

 A4. Install L20, the 500 uH noise filter inductor. It is the large cylinder

shaped component with wires coming from each end.

 A5. Install C42, 1500 uf, the first (and largest!) of the electrolytic

capacitors. The (+) side must be oriented as imprinted on your board,
toward L20.

 A6. Install C95, a 4.7 to 10 uf electrolytic.
 A7. Select D18, the 1N4002, the largest of the diodes used in your kit. It

has a black body with a gold band on one end. Notice the band towards
one end designating the cathode. This diode MUST be installed with its
ANODE in the ground hole nearest the back of the PC board. Solder the
anode end now, letting the diode body stand vertically on the board.

 A8b. Gently bend the cathode wire into its hole, pull it through so that it

is as short as possible with the diode standing vertically. Solder and trim
excess wire. NOTE: this is the basic method for installing all upright
parts.

 A9a. Voltage Regulator VR1 (type 7808 for 8 volts) is mounted with its

metallic back flat against the ground plane, secured by the small
machine screw and nut supplied. Identify VR1 correctly without mixing it
up with its 5-volt counterpart (VR2).

 A9b. Insert the 3 VR1 leads into the triangular set of holes while gently

bending the body back towards the board so that the mounting holes line
up. Secure VR1 to the board with the screw and nut. After VR1 is
mounted flat, solder and nip the 3 leads.

FX-146 • 73

 A10. Study the PC board, locate the triangular set of 3 holes for VR2

(type 7805), and insert VR2 so that the flat metal tab side is toward the
center of the board. Press VR2 in as far as it will go, solder and trim.

 A11. Near VR2, install C100, a 4.7 or 10 uf electrolytic, oriented for

correct polarity.

Stage A PROGRESS TEST:

The power input circuitry is completed and can be tested before proceeding.
Perform the test as follows:

 1. Make sure a 1 amp fuse is installed in the fuse holder.
 2. Connect the fused (+) and black (-) wires to a 12-volt battery or

power supply (12-15 volts DC).

 Connect the black (-) lead of a DC voltmeter or VOM to the ground

plane of the PC board.

 Study the PC board and locate the three points marked +12V, +8V and

+5V. (These connections are provided for convenience in later
modifying or experimenting.)

 With the power switch turned on, you should get meter readings of

+12V, +8V, and +5V respectively. (If your meter probe does not have a
fine enough point to make solid contact inside the holes at these 3
points, simply study the multi-color PC board illustration and look for
+12, +8 and +5 volts DC on PC board traces that lead to the 3 voltage
points.)

After you are satisfied that the power input circuitry is working correctly,
disconnect the 12 volt source.

WIRING THE PACKET I/O CONNECTION:
 A12. Press J1, the Packet I/O DIN connector into position. Before

soldering, make sure that the bottom of the jack is perfectly flat against
the board. It is best to solder only the middle pin first, check for
straightness, and then solder the other 4 or 6 points. (DIN jack styles
may vary; your jack may have simply the 5 connector pins, or 2 extra
pins for mechanical stability. Either style fits your PC board.) Directions
for installing hardware or unusual parts often require extra written detail.
You've just been through a lot of that in this stage.

The following steps are more typical of how many upcoming installation
directions will be given:

FX 146 • 74

 A13. Install C2, .001 uf disc capacitor. It may be marked .001 or 1 nf or

102. (102 means a one, a zero and two zeros which equals: 1000 pf.
1000 pf is the same as .001 uf. This notation (102) is similar to the
resistor color code to indicate resistance values.

 A14. Install C3, .001 uf.
 A15. Install C4, .001 uf.
 A16. Install C1, .001 uf (Don't confuse with C65).
 A17. Install C65, .1 uf. It may be marked .1 or 104. (As above, 104

means a one, a zero and four zeros = 100,000 pf which is the sa me
as .1 uf) (On the schematic, C65 is located near J4 and U4 and couples
packet audio to the microphone input line.)

 A18a. Select D9, one of the many 1N914 or 1N4148 switching diodes

used in the circuit. Don't confuse these diodes with the smaller PIN and
varactor diodes used in later stages. Notice the dark band at one end
designating the cathode and notice how the cathode end is imprinted
right on the PC board.

 A19. Install D9 paying attention to the orientation of the banded end.
 A20. Install R42, 2.2K (red-red-red). This is an "upright" installation like

D18, previously installed.

Almost all resistors will be installed this way. Like C65, R42 and D9 are
shown near J4 on the schematic and complete the External PTT connection
between U4 and J1.

No testing of the Packet components is required, but make sure all parts
values are correct and that D9 is oriented correctly.

FX-146 • 75

Stage B: Receiver Audio Amplifier

The secret to the fine performance of the LM380 audio amplifier lies in
careful selection and physical positioning of the several external components
required to complete its circuit. The LM380 is a self contained general
purpose audio amplifier capable of over 2 watts audio output with a voltage
gain of 50. Audio from the FM discriminator (U1) is fed through C7 through
the 10K volume control (R7) to pin 2, the amplifier input. The amplified
output at pin 8 is available through C34 to both the speaker jack and pin 4 of
the Packet I/O Jack. Capacitor C41 in series with R108 across this amplified
output are recommended good practice to prevent self-oscillation of the
amplifier IC.

Pin 1 is bypassed to ground through C48 in normal operation. If pin 1 is
grounded directly, the internal bias of the LM380 is upset, and the amplifier
is silenced. We are able to put this characteristic to practical use, using Q6
as a simple switch. When 8 volts is applied through R107 and D22 to the
base of Q6, the transistor collector grounds pin 1 of U2, thus silencing the
receiver during transmit. The COR output of U1 (pin 16) also mutes the
amplifier, a feature which we'll discuss in the context of Stage CR.

LM380 Audio Amplifier IC

FX 146 • 76

Stage B: Receiver Audio Amplifier and Speaker Connection

Stage B: AUDIO AMPLIFIER CIRCUIT ASSEMBLY:

Some of the Stage "A" steps required more detailed explanation than simply
inserting and soldering parts. As we move along, there will be more and
more short "one liners"! The following steps will complete a working audio
amplifier ready to power up and test.

 B1. Install U2, the LM380 IC. Be sure to orient the dotted or banded end

as illustrated. (The use of a DIP socket for U2 is NOT recommended,
even if you use sockets for the other IC's. Notice that most of U2's pins
are soldered to the PC board ground plane. This provides heat sinking
to the IC chip for proper heat dissipation.)

 B2. Install C48, 4.7 or 10 uf electrolytic, observe correct polarity.

FX-146 • 77

 B3. Install R108, 2 ohm (red-black-gold).

U

 B4. Install C33, .01 uf disc capcitor (marked .01 or 103).
 B5. Install C41, .1 uf disc capacitor (marked .1 or 104).
 B6. Install C34, 470 uf electrolytic. Watch out for correct polarity.
 B7. Similarly, install C29, 330 uf electrolytic.
 B8. Install C37, .01 uf disc capacitor (marked .01 or 103).
 B9. Install NPN transistor Q6. Be sure to have identified it correctly as

one of the five 2N3904 transistors used in your kit, (not one of the
2SC2498 RF transistors) and be sure to orient the flat side as illustrated.
Before soldering, press the transistor as far into its 3 holes as
reasonably possible.

 B10. Install R109, 47K (yellow-violet-orange). Note that this is another of

numerous vertical installations of resistors. The body of such resistors
should be snug against the board at the designated hole, with the other
wire neatly looped into the other hole without needless excess.

 B11. Cut three 8" lengths of hookup wire (or 8" of 3 conductor wire) to

connect the Volume Control to the three points designated on the PC
board. Strip and tin all six ends, referring back to Stage A instructions if
necessary or helpful.

FX PCBOARD

FUSE

 B12. Refer to the drawing

and correctly interconnect
the Volume Control's
three lugs to the 3
connecting points on the

IN

OUT

GND

PC board.

 B13. Use two 8" lengths

PWR

of hookup wire (or 8" of 2 conductor wire) to prepare the Speaker
Cable. Neatly strip and tin all 4 ends as in Step B11.

 B14. Solder both wires of one end of this speaker cable to the two

marked points near C37.

 B15. The other two ends of the speaker cable may be connected in any

of the following ways:

Standard:

SPEAKER JACK

 To J2, the 3.5 mm miniature speaker jack. The

3.5mm miniature jack is the larger of the two
miniature jacks supplied with your kit.

GND

FX 146 • 78

O

Optional:
To a test speaker, temporarily or to a speaker intended for regular use inside

or along with your FX- Transceiver.
 B16. Solder the speaker cable to your choice of speaker. Give attention

to the polarity marks on most bare speakers as well as enclosed units.
The wire from the point marked SPKR should be connected to the
speaker terminal marked (+).

Stage B: AUDIO AMPLIFIER TEST:
 1. Reconnect 12 volts DC as done for testing the power input circuit in

stage A. (We assume speaker hookup per B15.)

 2. Turn on power switch S1. All you should hear is one gentle "pop" in

the speaker. There should be no hiss or whistle. Touch the center
terminal of the volume control, and you should hear a moderate AC
hum. If you wish, connect a test oscillator or line-level audio source to
the input line to the control. You should hear a generous level of good
quality audio sound.

 3. Disconnect DC Power before proceeding with assembly.
 4. The volume control, speaker and other wired connections are installed

quite early in the assembly sequence so that tests can be performed
periodically during assembly. The disadvantage to this approach is that
there is considerable wear and strain on the various wire connections as
the PC board is repeatedly flipped back and forth during assembly. This
is a serious consideration because most radio malfunctions are due to
broken wires and not component failure. For this reason, such wiring is
usually done at the final stage of assembly. To minimize damage to the
controls and wiring, use a wire ty-rap, plastic bag tie or a scrap piece of
hook-up wire to hold down this group of wires temporarily. A convenient
point to loop your tie through is one of the PC board mounting holes
near U10.

FX-146 • 79

STAGE CR: FM RECEIVER CIRCUIT
DUAL CONVERSION SUPERHET WITH IF FILTERS

FX 146 • 80

Stage CR: Integrated FM RECEIVER (with Squelch Control)

This step is named "CR" so that the assembly step numbers do not
resemble designator numbers for capacitors.

To fully appreciate the marvel of U1, the MC13135 FM Receiver IC, one
would need to study the schematic diagram of any FM receiver more than
15-20 years old, including fully "solid-state" models. The MC13135 IC is truly
a "Receiver-on-a-Chip." The cluster of parts to assemble and understand
around U1 is minimal in comparison to what was previously required for a
quality FM receiver circuit

For years, Ramsey Electronics has employed a similar IC, the MC3359 as
the heart of our popular FM receivers for the 10, 6, 2 and 1.25 Meter bands.
We adopted the MC13135 IC for the FX-series because of its features
especially suited for state-of-the-art FM voice and digital communications
requirements.

The MC13135 is a complete FM narrowband receiver from antenna input
(pin 22) to audio preamp output (pin 17). The low voltage dual conversion
design results in low power drain, excellent sensitivity and good image
rejection in narrowband voice and data link applications. The FX146
implementation of this IC yields increased image rejection by using a 21.4
MHz first IF rather than the traditional 10.7 MHz. A precision 2-pole crystal
filter (FL1) is used for the 21.4 MHz first IF.

The receiver IC is so complete that it includes an internal local oscillator
requiring only a crystal across pins 5 and 6 to establish the basic operating
frequency. Our design injects the output of the transceiver's PLL-controlled
VCO through C35.T

As an option, a helical resonator module can be installed in the front end RF
amplifier area for excellent receiver performance in high RF environments.

The first mixer amplifies the signal and converts this RF input to 21.4 MHz.
The second internal mixer is where the 2nd IF frequency of 455 KHz is
achieved by mixing with the 21.855 MHz oscillator. The oscillator circuit is
internal to U1; the crystal is Y1, 21.855 MHz.

The 455 KHz second IF output (pin 7) requires filtering to provide good
adjacent channel rejection. A high performance 6 pole ceramic filter is used.
Filters such as this are used in virtually all FM radio transceivers. Let's
summarize the basic "double-conversion" principle for receivers, using the
national 2 Meter band simplex channel, 146.52 MHz as our working
example:

1. An antenna could be connected directly to pin 22 of U1, and our receiver­on-a-chip would indeed work. The antenna would bring in our theoretical test
signal of 146.52 MHz as well as every other signal in the radio spectrum.
Since that's a bit much to expect the receiver to handle, we will build up that
network of filters, tuned circuits and RF preamplifiers that constitutes Stage

FX-146 • 81

"DR" of this project. The purpose of the "DR" circuitry is to filter out or at
least diminish other signals while boosting signals in the 146 MHz region.

2. The First IF converts the incoming 146.52 MHz signal down to 21.4 MHz.

In order to do this job, the IC's 1st IF Mixer needs ANOTHER frequency
source to mix with the signal presented by the antenna through the filters
and preamps of Stage DR. This other signal must be VERY precise since
the mixer output is fed into a very sharp crystal filter at 21.40 MHz.
Specifically, the 1st IF mixer seeks a second signal that is 146.52 - 21.40 =

125.12 MHz.

3. Supplying the needed 125.12 MHz "local-oscillator" input signal is the job

of the tuneable or programmable oscillator section of any receiver, whether
AM-FM-SSB, HF or VHF, etc. In this case, take it on faith that the VCO
(Stage F), controlled by the PLL Frequency Synthesizer (Stage H) will
deliver the precise 125.12 MHz local oscillator signal needed by U1's 1st IF
Mixer. The VCO signal is applied to pin 1.

4. No matter what we tuned in, the 1st IF Mixer section of U1 delivers the

incoming signal at 21.4 MHz to the next section of U1. This next section
wants to do yet ANOTHER frequency conversion! Which is where we get
the ideas of "dual-conversion" and "2nd IF." This time, though, no more
"variable" input is expected from beyond the FM IC's basic functions. Crystal
Y1, 21.855 MHz, completes another internal oscillator. Its output is mixed
with the steady 21.4 MHz signal from the 1st IF Mixer, and we can start to
see the whole picture:

146.52 - 125.12 = 21.400 MHz

21.855 - 21.400 = 455 KHz

5. The 146.52 MHz signal at the antenna has gone through quite a sorting

and converting process. It now appears to additional sections of U1 as a 455
KHz signal that needs "demodulating," a way of saying: detecting, analyzing,
decoding, or just making something intelligent out of it all. The MC13135
employs a conventional quadrature detector. Inductor L1 is the quadratu re
coil, requiring a simple one-time adjustment.

The exact process of "detecting" intelligible FM voice or data from the 455
KHz 2nd IF is the job of the remaining sections of the MC13135 IC. Because
there's much more of this transceiver circuit to discuss and understand,
please study other sources if you are not clear on concepts such as Limiter,
FM Discriminator, Quadrature, phase shift, and so forth. As long as you just
see the general flow of how a 146.52 MHz. VHF FM signal can become
intelligible audio input to the U2 speaker amplifier (Stage "B"), we're doing
fine for now.

FX 146 • 82

ADDITIONAL RECEIVER IC FUNCTIONS AND FEATURES
In addition to audio output at pin 17, a separate high speed data output (up

to 35000 baud) is available and may be linked directly to a packet TNC or
other data controller using the jumper wire pad provided on the PC board.
The MC13135 is capable of detecting true FSK (frequency shift keying) in
addition to AFSK.

The receiver has good "hysteresis" characteristics, the ability to hold the
squelch open once it has been broken by a marginal signal, even if the
signal becomes weaker. The IC also has carrier detect circuitry which is put
to good use in the transceiver design by providing very effective squelch
action. The squelch is activated by signal strength, not by noise. When no
carrier is detected, the voltage at pin 16 is high, which causes Q6 to mute
the audio amplifier U2 as explained in Stage B.

When a carrier is detected, the voltage at pin 16 drops low, turning off Q6.
Resistor R13 permits squelch adjustment.

Finally, the carrier detect circuitry affords the same COR ("Carrier Operated
Relay") action as needed in any repeater, which is why the output is also
available on the PC board, designated "COR." It is up to creative users to
determine their own practical implementations for this feature.

Stage CR ASSEMBLY PROCEDURE:

 CR1. Install U1, the MC13135 24-pin DIP FM Receiver IC. Make sure

all 24 pins are visible through the holes before soldering and be very
sure that the notched end is oriented as illustrated.

Install the following resistors:

 CR2. Install R11, 47K ohm (yellow-violet-orange).
 CR3. Install R5, 10K ohm (brown-black-orange).
 CR4. Install R4, 68K ohm (blue-gray-orange).
 CR5. Install R24, 10K ohm (brown-black-orange).
 CR6. Install R119, 270 ohm (red-violet-brown).
 CR7. Take a moment now to double check your work. Touch up any less

than perfect solder connections.

Install the following capacitors:

 CR8. Install C16, .01 uf disc capacitor (marked .01 or 103).
 CR9. Install C5, .01 uf disc capacitor (marked .01 or 103).
 CR10. Install C9, 4.7 or 10 uf electrolytic, observe correct polarity.

FX-146 • 83

 CR11. Install C8, .1 uf disc capacitor (marked .1 or 104).
 CR12. Install C13, .1 uf disc capacitor (marked .1 or 104).
 CR13. Install C14, 27 pf disc capacitor (marked 27).
 CR14. Install C26, .01 uf disc capacitor (marked .01 or 103).
 CR15. Install C6, .1 uf disc capacitor (marked .1 or 104).
 CR16. Install C7, 4.7 or 10 uf electrolytic. Watch polarity (or U1's aud io

won't reach U2!) The polarity doesn't always show up on the silkscreen
so consult the pictorial for proper orientation.

 CR17. Install C13, .1 uf disc capacitor (marked .1 or 104).
 CR18. Select and install FL2, the rectangular plastic block with 3 thin

pins. It fits only one way. This is the 6 pole, ceramic 455 KHz IF filter
network. Verify that filter FL2 is properly seated and soldered. So far,
most disc capacitors installed have been from your endless supply of .01
and .001 capacitors. If you have not done so already, now would be a
good time to sort and organize all your "picofarad" capacitors, ranging in
value from 2 to 100 pf. Correct selection of these values will be essential
throughout the RF stages of your transceiver.

 CR19. Install C10, .001 uf. (marked .001 or 102).
 CR20. Install C15, .01 uf (marked .01 or 103).
 CR21. Install C12, 47 pf (marked 47).
 CR22. Select and install Y1, the 21.855 MHz. crystal. It must be snug

on the board before soldering. [Be sure not to confuse Y1 with Y2, the

10.240 MHz. crystal which will set the Reference Frequency for the PLL
Synthesizer, or with FL1, which has 3 wires.]

 CR23. Install L1, the 455 KHz shielded coil marked LB53303HK. Make

sure it is seated squarely on the board before soldering. Solder all pins.

 CR24. Install C101, 4.7 or 10 uf electrolytic, observe polarity.
Install these following resistors:

 CR25. Install R6, 3.3K ohm (orange-orange-red).
 CR26. Install R8, 47 ohm (yellow-violet-black).
 CR27. Install R2, 1K ohm (brown-black-red).
 CR28. Install R1, 220K ohm (red-red-yellow)

FX 146 • 84

 CR29. Install FL1, the 21.4 MHz IF filter. Its 3 wires may be inserted

either way; make sure its body is snug against the top of the board
before soldering.

 CR30. Prepare three 8" lengths of hookup wire for connecting R13, the

100K Squelch Control. Strip back ¼" from one end of each wire. Tin all
ends.

• Select a wire, connect one stripped end to the three connecting

lugs of the control.

• Observe the diagram and locate the squelch wire connections on

the printed circuit board.

• Connect the three wires to the printed circuit board as shown in the

diagram. Pay careful attention to the wire placement as not to wire
the
squelch pot in

SQUELCH

“backwards”.

FX PCBOARD

R6

C16

FL1

 CR31 Install D20, 6.2 volt zener diode (gray body, black band).

Observe correct placement of the banded cathode end. Zener diodes
are widely used as voltage regulators. They have the interesting
property of keeping a constant voltage across their terminal leads.

 CR32 Install Q17, 2N3904 transistor, observe the flat side.
The last 4 steps involved the building of a voltage regulator to supply a

steady source of voltage to the receiver IC chip. At this point in your work,
you could actually receive strong local signals by connecting an antenna
wire at C17 and a high frequency signal source (e.g. a signal generator) to
the input of U1 at pin 1. The signal you would receive would be on a

FX-146 • 85

frequency of the signal generator frequency plus 21.4 MHz. Because we
have not yet constructed any of the input circuitry (Stage DR), you would
also hear any signal on the signal generator frequency minus 21.4 MHz.

FX 146 • 86

FX SERIES TRANSCEIVER Simplified Receiver Block Diagram

ANTENNA

LOW

PASS

FILTER

HIGH

PASS

FILTER

21.885 MHz
LOCAL

OSCILLATOR

LIMITER

Q3

RECEIVE

PRE-AMP

21.4 MHz
FILTER,

AMPLIFIER

SECOND

MIXER

6 POLE

455 KHz

FILTER

IF

BAND

PASS

FILTER

Q2

RECEIVE

PRE-AMP

FIRST

IF

MIXER

PLL CONTROLLED

VCO

PROGRAMMED

21.4 MHz

LOWER THAN

DESIRED

RECEIVE SIGNAL

FM

DISCRIMINATOR

AUDIO

AMPLIFIER

Q6

RECEIVER

MUTING

FX-146 • 87

SPEAKER

Stage DR: Receiver Tuned RF Input and Preamp

FX 146 • 88

Stage DR: Antenna Input and RF Preamplifier

The operation of the FM receiver IC was discussed in Stage CR. The
purpose of the following circuitry is to minimize the strength of unwanted
signals and to boost signals in the 140 - 160 MHz range before they reach
the 1st mixer input of U1 (pin 22). In addition, the circuit includes PIN diodes
for proper T-R (transmit-receive) switching.

Let's follow the signal path briefly from the antenna jack, remembering that
the antenna is "picking up" thousands of signals from all over the radio
spectrum. Capacitor C71,19,72 and L12,22 form a low pass filter,
suppressing unwanted signals that are higher than the desired receiving
range. The filtered signals are coupled through C47 to Q3, a low noise
preamp stage and then on to a band pass filter network consisting of
C30,31,28,104 and L2,5,6. For use in very high RF environments, an
optional helical filter may be installed in place of this band pass filter.

Helical filters provide excellent filtering characteristics, although at a cost ­typically $20 to $25. We leave this option open to you!

The RF present now strongly favors signals that are in the desired frequency
range of interest. This RF is amplified again by Q2 and then applied to U1,
the main receiver IC chip. The RF from the antenna input to U1 now can be
said to be restricted to the desired tuning range of the transceiver. Unwanted
signals have been doubly rejected, and the desirable signals have been
doubly amplified.

Take a look at PIN diodes D2, D6 and D7. These tiny diodes are amazing
devices which have made relays and so forth all but obsolete for T-R
switching purposes. To put it simply, a PIN diode can pass RF energy either
way when it is turned on by DC voltage and also block RF from the other
direction when it is not powered by DC. Just picture RF passing with the
anode "arrow" and picture the cathode band as a barrier.

The symbols "+8R" and "8T" mean that voltage is present at such a point
during Receive or Transmit only, not both at the same time.

During Receive, D6 is "on" and permits RF to flow from the antenna through
C47 to the filter and amplifier stages just discussed. Because any DC device
needs a ground connection as well as +DC, D6 is grounded through RF
choke L17, which prevents the antenna RF from being shorted to ground.
During Transmit, D7 passes RF from the transmitter to the antenna, and L17
again prevents loss of RF to ground.

During transmit, D6 is blocking transmitter RF from the receiver circuit.
For maximum protection of the more delicate receiver circuitry, D2 is
turned on during transmit to short any stray RF directly to ground.

FX-146 • 89

STAGE DR ASSEMBLY:

Be very attentive to capacitor values (in picofarads) and to coil descriptions
throughout this section.

 DR1. Correctly identify and install PIN diode D6. It is the only BA479

used in the circuit, and its number is stamped plainly on the diode body.
Be sure to orient the cathode end correctly!

 DR2. Install L17, 2.2 uH in upright position with the inductor's body in the

designated hole. This is a molded inductor, resembling a resistor but is
larger. Look for 2 red bands on its body.

 DR3. Because it must dissipate slightly more power, resistor R54 is

larger than most of the resistors used in this circuit. Its value may be 200
or 220 ohms (red-black-brown, or red-red-brown). Install R54 in upright
style.

 DR4. Install C47, 100 pf (marked 100 or 101).
 DR5. Install R28, 470 ohms (yellow-violet-brown).
 DR6. Install C25, 100 pf (marked 100 or 101).
 DR7. Install C27, 8.2 pf disc (marked 8.2).
 DR8. Install D4, type 1N914 or 1N4148. Orient the cathode band

correctly.

 DR9. Install C53, .01 uf disc capacitor (marked .01 or 103).
 DR10. If you think that transistor Q3, type NE021,

is tiny, wait until you install C75, the SMT
(Surface Mount Technology) or "chip" capacitor
at Q8, the Transmit Final Amp! Study the drawing
and Q3 itself before removing the device from its
protective paper.

 DR11. The longest of the three leads is the

collector, which points to R12, as pictured.
Remove Q3 from its adhesive paper, bend all three leads down 90
degrees, and insert as illustrated.

 DR12. After making sure that the body of Q3 is snugly against the PC

board and correctly oriented as shown above, solder and trim all three
wires. That's all there is to it!

FX 146 • 90

Install the following resistors, each in upright position:

 DR13: R16, 47K ohm (yellow-violet-orange).
 DR14: R17, 470 ohm (yellow-violet-brown).
 DR15: R12, 100 ohm (brown-black-brown).
 DR16. Install C20, 100 pf. (marked 100 or 101).
 DR17. Install C30, 47 pf (marked 47).
 DR18. Install L5, .015 uH, a small 2 turn wire coil.
 DR19. Install C28, 47 pf (marked 47).
 DR20. Install L2, another .015 uH small 2 turn wire coil.
 DR21. Install L6, yet another 2 turn .015 uH coil.
 DR22. Install C31, 47 pf (marked 47).
 DR23. Install C104, 8.2 pf.

INTERMISSION: Notice how our work is methodically creeping toward all
the FM IC circuitry you did in Stage CR ?

 DR24. Install C22, 100 pf (marked 100 or 101).
 DR25. Install R14, 47K ohm (yellow-violet-orange).
 DR26. Install R10, 470 ohm (yellow-violet-brown).
 DR27a. Select a 2SC2498 NPN RF transistor. This is the first of such

transistors used in this circuit, they are marked with 'C2498' on the flat
side. Again, do not confuse these with the more common 2N3904 (or
similar) transistors such as already installed.

 DR27b. Install Q2, 2SC2498 transistor.
 DR28. Install C17, 100 pf (marked 100 or 101), and all your work in this

stage is now connected to the RF input of U1.
Stage DR Progress Note:
No other testing is required at this point other than to double-check the

accuracy of your parts installations. However, experienced builders will
recognize that VHF signals could now be received very well by connecting
an antenna and tuning a signal generator coupled to U1 provided that the T­R circuitry is operational. A more useful preliminary receiver test will be
conducted after we complete the VCO stage.

FX-146 • 91

Stages E - F: Transceiver VCO (Voltage Controlled Oscillator) and
Buffer Stages

FX 146 • 92

Stage E-F: The FX Transceiver VCO

The VCO (Voltage Controlled Oscillator) provides basic frequency control for
both transmit and receive modes. It is essential to understand its function in
the transceiver circuit. Q7 is the oscillator transistor and the key VCO
components are L7, D3 and D23.

Think of the VCO for now as just a simple 'VFO' type RF oscillator whose
output frequency can be changed by adjusting the slug in L7. Notice that
there are no capacitors, either fixed or variable, to form a 'tuned-circuit' with
L7. Instead, varactor diodes D3 and D23 perform this function. (A varactor
diode changes capacitance in step with the amount of voltage applied
across it.) If the output of this simple oscillator reached U1 through C35, you
would certainly be able to receive any signals on a frequency determined by
that oscillator frequency plus or minus 21.4 MHz, the Receiver 1st IF.
Similarly, if the oscillator output could reach Q9 and Q8 in the transmit
section, or even the transmit buffer, Q10, some sort signal could be put on
the air.

After the VCO is assembled on the PC board, the interested builder has the
option of experimenting with it in receive mode before proceeding. The VCO
must be capable of considerable frequency range. To receive a signal at 140
MHz, the VCO must tune to 140 MHz minus 21.4 MHz or 118.60 MHz. To
transmit at 160 MHz, it must tune to 160 MHz. This indicates a tuning range
of over 40 MHz!

For now, consider Q5 and Q16 to be buffer stages for oscillator Q7 and that
transistor Q4 does some nifty voltage filtering that we'll explain later on.
What we have so far is a master oscillator for the transceiver that can be
tuned by varying the voltage applied to the varactor diodes. All we really
need now is some precision way of controlling the voltage applied to those
varactor diodes so that we can put that oscillator on any VHF channel we
want with 5 KHz precision. And this control obviously must be extremely
stable, since a change of only a few picofarads can tune through many MHz
of VHF spectrum. We know we can get stability by using a crystal oscillator,
but that would not allow us to operate on a multitude of channels without
changing crystals for each channel. How can we get such precision
performance from small tuning diodes, a very ordinary shielded coil, and a
transistor with its supporting capacitors and resistors?

We guess already that the answer must lie in the functions of the Frequency
Synthesizer IC. However, the key to grasping what this IC really does lies in
understanding TWO concepts: frequency synthesis and the "Phase Locked
Loop" or PLL. The more of a handle that you can get on these two
interconnected ideas, the less mysterious will be your FX transceiver as well
most other modern radio gear - from ham transceivers to car stereos to
cellular phones. The VCO is an integral part of the phase locked loop. You
can read ahead about PLL and synthesis in the next section, or you can
proceed with building and testing the VCO alone.

FX-146 • 93

VCO CIRCUIT SUMMARY:

The control voltage for the D3 and D23 varactor diodes is supplied through
R47 and R25 by the output of U5:A in the PLL synthesizer circuit.

We know already that there must be a 21.4 MHz difference between the
receive and transmit frequencies of the VCO. This swing cannot be
accomplished by PLL programming alone. The VCO must be able to stay "in
range" with the synthesizer. D3 and D23 work in series during transmit,
which reduces their total capacitance to one-half (per the standard formula
for capacitors in series). For example, if a given control voltage runs both
diodes at 5 pf, the actual capacitance is 2.5 pf. In receive, the +8R through
D1 causes D3 to be shunted by C39, which causes D23 alone to control the
VCO L-C circuit, introducing twice as much capacitance and thereby
lowering the frequency.

Transistor Q5 is a common base buffer which affords good isolation, low
input impedance and broadband characteristics. The output from Q7 is fed
into U3, 12017, a Ã64/65 prescaler which divides down the VHF signal to a
lower frequency which the PLL chip can process. The output is further
buffered and amplified by Q16, the VCO buffer which feeds U1 through C35
for receive, and Q10 through C56 for transmit.

Another important role of the VCO is that it is the stage that is modulated by
microphone amplifier U4, which is discussed in Stage M. Notice that the
microphone amplifier output is coupled through C62 directly to the voltage
control line for the varactor diodes. Therefore, any voltage variation imposed
on that line will vary the VCO frequency in step with that variation. If the
frequency is varied in step with speech patterns or other audio signals such
as tone shifts, we are generating 'frequency modulation', hence 'FM'.

D5 and R31 perform an interesting function. Remember that the VCO control
voltage has a range of about 1.0 volts DC (low frequency) to 7.0 volts (high
frequency). Therefore, more modulation voltage is needed at higher VCO
frequencies. As the VCO control voltage increases, D5 turns on and places
R31 in parallel with R33, reducing the resistance in the line to half and
thereby increasing available modulation voltage.

Finally, it should make sense that the VCO should have a very pure source
of well-filtered DC, completely free of AC hum, alternator whine or other
disturbance. R19 and 47 uf C40 form a basic low pass filter. Transistor Q4
serves as an electronic capacitance multiplier. The actual effect of the filter
is that the beta of Q4 multiplies the 47 uf to the equivalent of installing a
huge 4000-5000 uf capacitor in the VCO area.

FX 146 • 94

Stage E: BASIC VCO ASSEMBLY

In this Stage, we will assemble the basic VCO (Voltage Controlled Oscillator)
circuit. Understanding the function of this stage is especially important for
knowing how the FX transceiver works.

 E1. Select and install shielded coil L7, stamped 84885-5. It fits in two

different ways, and either way will work. Be VERY sure BEFORE

soldering that this coil is seated snugly on the PC board.

 E2. Install C43, .001 uf (marked .001 or 102).
 E3. Install C54, 56 pf disc capacitor (marked 56).
 E4. Install C51, 22 pf disc capacitor (marked 22).
 E5. Install R30, 51 ohm (green-brown-black).
 E6. Install R22, 10K ohm (brown-black-orange).
 E7. Install R18, 270 ohm (red-violet-brown).
 E8. Install R66, 47K ohm (yellow-violet-orange).
 E9. Install Q7, NPN type 2SC2498. Before soldering be sure to identify

Q7 correctly and to insert it with its flat side as shown in the parts

diagram.
 E10. Install varactor diode D23, type BB505. It has a black body with a

white band. Be certain of correct diode identification and orientation of

cathode (WHITE band) end.

 E11. Similarly, install D3, also type BB505. Watch that polarity!
 E12. Install C36, .01 uf disc capacitor (marked .01 or 103).
 E13a. Install C40, 47 uf electrolytic. Be sure to orient polarity as shown.
 E13b. Install R19, 10K ohm (brown-black-orange).
 E14. Install C39, .001 uf. disc capacitor (marked .001 or 102).
 E15. Install D1, type 1N914 or 1N4148.
 E16. Install R15, upright, 1K ohm (brown-black-red).
 E17. Install C99, .01 uf disc capacitor (marked .01 or 103).
 E18. Install R25, upright, 47K ohm (yellow-violet-orange).
 E19. Install Q4, NPN type 2N3904. Be sure to orient flat side as

illustrated.

FX-146 • 95

 E20. Install R35, upright, 100K ohm (brown-black-yellow). R35 is

between positions for D5 and C62.

Steps E1-E20 are presented as a group primarily as a help in visualizing the
location of the VCO on the PC board. You have built up the VCO itself and
the capacitance multiplier voltage filter provided by C40, Q4, etc. After
double-checking the accuracy of your work, proceed with installing the VCO
related components in Stage F.

Stage F: VCO Buffers, PLL Synthesizer, ÷65/64 Prescaler

Install the following group of parts for Q5:

 F1. C45, 100 pf disc capacitor (marked 100 or 101).
 F2. C52, .001 uf disc capacitor (marked .001 or 102).
 F3. R26, 51 ohms, (green-brown-black).
 F4. R27, 47K, upright (yellow-violet-orange).
 F5. R20, 270 ohm, upright (red-violet-brown).
 F6. R23, 100 ohm, upright (brown-black-brown).
 F7. Install Q5, NPN type 2SC2498. Be sure to select the correct

transistor type and to orient the flat side as pictured.

Install these capacitors associated with U3:

 F8. C21, 10 pf disc capacitor (marked 10).
 F9. C46, 100 pf disc capacitor (marked 100 or 101).
 F10. C50, 100 pf disc capacitor (marked 100 or 101).
 F11. C38, .001 uf (marked .001 or 102).
 F12. C57, .001 uf (marked .001 or 102).
 F13. Install C32, 100 pf disc capacitor (marked 100 or 101).
 F14. Install Q16, NPN type 2SC2498. Be sure to select the corre ct

transistor type and to orient the flat side as pictured.

 F15. Install R106, 10K ohm (brown-black-orange).
 F16. Install R105, 100 ohm (brown-black-brown).
 F17. Install L21 near R105. This .33 uH. molded inductor is quite small,

green body with 2 orange stripes. Before soldering, make sure there is
no excess wire length above the board.

FX 146 • 96

 F18. Install C35, 100 pf disc capacitor (marked 100 or 101). C35 couples

the VCO buffer to the receiver IC.

 F19. Install C94, a 3.9 pf disc capacitor (marked 3.9).
 F20. Solder 1/4" lengths of bare wire (trimmed from resistors or

capacitors) in the two test point holes marked TP2 and TP3. Study the

following optional test procedure before installing a similar test point at

TP1.
F21: TEMPORARY RECEIVER PTT/T-R CONNECTION
OMIT this step if you prefer to install ALL transceiver parts before any testing

or use of the Receiver alone. If you wish to conduct further tests or put the
receiver to work, it is necessary to solder a 5" length of hookup wire from
the hole marked "+8R" (near Q13, R112) to the hole marked "+8V" near
C29. In lieu of the switching done by the PTT circuit (Stage M), this
temporary jumper applies +8V to all +8R points on the board. (You also
have, of course, the option of wiring the microphone input and PTT circuitry
before testing the receiver.)

Even if you do not perform the following test, be aware that there is one
more step following this discussion (F22) - please don't forget to do it.

OPTIONAL VCO RECEIVER TEST OR INSTRUCTIONAL
DEMONSTRATION

At this point in building your transceiver, the VCO is functional but is lacking
any control voltage to varactor diodes D3 and D23 that would permit tuning.
Supplying this precision controlled voltage is, of course, the function of the
PLL Frequency Synthesizer that will be constructed next. However, for those
who would benefit from such a test or demonstration, it IS fairly easy at this
point to set up temporary manual or "analog" tuning with an ordinary
potentiometer.

Notice on the schematic diagram that the control voltage to the tuning diodes
comes from U5A through R47 and R25. Notice that a Test Point (TP1) is
conveniently located at R25. The purpose of TP1 is to permit measurement
of the precision voltage to the varactor diodes generated by the frequency
synthesizer's phase detector. Since no such voltage is yet reaching TP1, we
can put it there ourselves! If we connect a potentiometer as illustrated below,
the wire soldered to TP1 can be trimmed down later to serve as the intended
test point. The potentiometer will vary the voltage to D3 and D23, thereby
varying the VCO frequency and tuning your receiver.

FX-146 • 97

VCO AND RECEIVER TEST PROCEDURE:
 1. Make sure work area is tidied up and that the PC board has been

checked for stray scraps of wire, etc.

 2. Use your own hookup wire and potentiometer to connect to TP1, +8V

and GND as illustrated.

 3. Turn power switch OFF and squelch fully counter clockwise.
 4. Connect 12V DC, speaker and antenna (2' of wire will do).
 5. With power on and volume at a low level, s-l-o-w-l-y turn the

temporary tuning potentiometer. See if you can hear a local repeater,
nearby transmitter or business band transmissions. Perhaps the easiest
signal to hear is the local NOAA weather transmitter located around

162.5 MHz. Because the control is sweeping through FORTY MHz of
spectrum, actually tuning in a station will be VERY touchy.

The demonstration can be more interesting and useful if a digital voltmeter is
added to monitor the voltage changes at TP1, and a Ramsey Frequency
Counter is connected to TP2 or the top of R113. REMEMBER that the
indicated VCO frequency is 21.400 MHz LOWER than any signal you
happen to tune in. Observe how much frequency change there is per .1 volt
or less of voltage change. Stay on a given frequency for a minute or so and
notice how the indicated frequency drifts slightly either up or down. This
observation helps us appreciate the precision control that will be offered by
the PLL circuit. Finally, notice that the higher the voltage applied, the lower
the varactor diode's capacitance which means the higher the VCO
frequency.

If you do have a meter and counter connected, an initial setting of the slug in
L7 can be made now. Adjust the voltage for 4.0 volts and tune L7 to
approximately 138 MHz. (Note: final tuning of L7 will be even easier after the
PLL circuitry is completed). When you are finished with this optional
test,disconnect DC voltage. Then, cut the wire to TP1, leaving 1/4" soldered
in place to serve as a permanent test point. If you do not wish to conduct this
test, simply double-check the accuracy of your work in this stage and
proceed to the Frequency Synthesizer section.

 F22. Install U3, IC type 12017. Do not use a socket for U3, just be sure

to orient the notched end as shown on the board.

FX 146 • 98

RAMSEY FX-146 VHF FM TRANSCEIVER
KIT ASSEMBLY PHASE 2:

• Stage G: Understanding and Building the PLL Frequency

Synthesizer

• Stage H: Building and Programming the Diode Matrixes

• Stage M: Microphone Amplifier and PTT Circuit

• Stage "TC": Preparing Transmitter Coils, RF Chokes

• Stage "TO": Other Transmitter Stage Preparation

• Stage TX: Transmitter Buffer, Driver and Final

Each set of Assembly Instructions is introduced by an explanation of how
that part of the circuit works and what it is for. LEARN as you build!

ALSO INCLUDED IN THIS SECTION:

• Detailed Explanation of PLL Frequency Synthesis

• How to Program the Synthesizer

• EASY PLL Alignment Directions

Study the REFERENCE SECTION for additional help and tips on Frequency
Programming.

FX-146 • 99

Stage G: The PLL Synthesizer: Understanding and Assembly

FX 146 • 100