2 METER AMATEUR PLL
SYNTHESIZED FM
TRANSCEIVER 140 - 180
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 !
Published in Three Sections:
? FX-series General Reference Information
? Kit Assembly Phase I: Circuit Stages A through F
? Kit Ass embly Phase II: Circuit Stages G through TX
Plus:
? Fold-out Schematic Diagram
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. Gro wing 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 FTR -146 for
two meters. The FX Transceiver design was developed in immediate
response to those builders' suggestions, wish lists and inquiries. This
publication is dedicated with deep thanks to all those F TR-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
(716) 924 -4560 Fax: 924-4555
FX 146 • 2
FX-146 • 145
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 • 144 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
FX-146 • 143
output by spreading the coils.)
type
conversion superhet
*Common faults:
? Low supply voltage.
? Improper tuning.
? Improper output power measurement.
Receive Section Faults:
(manual pages ref. 20-21, assm 22-24, assm 30)
1. Poor or no receive. Lots of audio hash.
a. Check for proper VCO frequency.
b. Ensure pin diode D6 is forward biased (anode ~ 2.7VDC, cathode
~ 2.0 VDC) and pin diodes D2 and D7 are reverse biased (D2
anode ~ 0VDC, D7 anode ~ 0VDC, cathode ~ 2.0VDC).
c. Check preamp transistors Q2 and Q3 for proper operation. (The
Base lead on both transistors should be appox. .6 - .7 VDC)
*Common faults:
? Solder shorts between components.
? Improper value components. (There’s a few each of the 470 ohm
and 47K ohm resistors!)
2. No receive. Audio is completely quiet.
a. Check Q6. (Q6 turns off the LM -380 audio amp in transmit and
when squelched.) Q6 should be turned off during receive when
unsquelched. (approx. 0 VDC on the Base lead.)
Misc. Faults:
1. The darn thing is blowing fuses.
a. Check for a short to ground on one of the supply lines. (+12V,
+8V, +5V) You may have to remove a few components to isolate
the short.
2. Low receive audio, or low transmit audio.
a. Ensure correct connections between the speaker and microphone
jacks and the circuit board. (ex. The ground and speaker wires
are switched. Since the ground is common for the speaker and
mic on your average speaker-mic, you have just grounded the
audio output of your tra nsceiver.)
If All Else Fails:
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 -
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-
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 • 142
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 fool proof 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 abo ut what you'll create from those bags of
back to the manual, isn’t our “n” number for 10 Khz right about 2?
c. Some coincidence! Now we can guess that our fault is between
the # 2 position trace and the input to U6.)
d. Some channels are off frequency by different amounts. (Refer to
preliminary check # 5)
*Common faults:
? Improper diode programming.
? Solder shorts between traces. (There’s a lot of traces betwe en U6
and the diode matrix!)
Transmit Section Faults:
(manual pages ref. 26, assm. 72)
1. No power output.
a. Check for proper VCO frequency.
b. Check +8T and +12V to the`transmit Buffer, Driver, and Final
stages.
c. Ensure D7 is forward biased. (approx. 7.2 VDC at junction of L17
& R54)
d. Double check all components in transmit section for proper value
and placement.
e. Check for heat on Q9 and Q8. (If they’re warm, chances are
they’re working)
*Common faults:
? Coils touching the board.
? Solder shorts between components.
? Solder short on Q8 base to ground.
2. Low Output Power. (We see 4-6 watts normally. If your figures are
within 20%, consider this ok.)
a. Ensure DC input to the transceiver is a full 13.8 VDC. (If your lead
wires are too long, they could be dropping excess voltage.) Check
for proper voltage on the board, not at the power supply.
b. Ensure +8T is a full 8VDC. (This is the supply voltage for the
transmit Buffer.)
c. Try adjusting the coils slightly, and then retunin g for maximum
power output. (L12, L13, L15, L16, and L22 are purposely
designed to have extra inductance so you can peak the pow er
FX 146 • 6
FX-146 • 141
help after all.
VCO & PLL Faults:
(manual pages ref. 21-24, assm.35-36, 43 -48, 52-57)
1. PLL not locking. (L7 will not set correct voltage @ TP1)
a. Check for proper programming inputs to U6 (pins 10-25). If
VOLTAGES ON U6 @ 146.52 MHZ IN RECEIVE/TRANSMIT
pin ~ VDC pin ~ VDC pin ~ VDC pin ~ VDC
20 ~ 0/0 16 ~ 0/0 12 ~ 5/0 24 ~ 0/5
19 ~ 5/5 15 ~ 0/0 11 ~ 5/5 22 ~ 0/0
18 ~ 5/5 14 ~ 0/5 10 ~ 0/5 21 ~ 0/0
17 ~ 0/5 13 ~ 5/0 25 ~ 0/5
incorrect, fault lies between diode matrix and inputs to U6.
b. Check VCO for proper range of operation. Follow the test on page
assm. 39-40 of your manual. (You will need to remove R47 for
this test) The VCO should tune smoothly from approx. 120 Mhz
to 180 Mhz as seen on TP2. If not, check area of Q7. TP3 should
indicate approx. 1/64 of the frequency at TP2. If not, check area of
U3.
23 ~ 0/0
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!
*Common faults:
? Solder shorts between traces.
? Diodes installed in reverse.
? Excess lead length on VCO components
? Improper frequency readings. Try probing on other components,
(Q7, Q16, R113) for a better reading.
2. VCO Frequency Incorrect.
a. If freq uency is incorrect on one channel only, recheck diode
programming for that channel.
b. A few channels are off by the same amount. Check for similar
diode programming on these channels to find your faulty area.
(ex. Let’s say our faulty channels are all off by 10 Khz, and they
all use the # 2 diode programming position. Hmmm, if we refer
FX 146 • 140
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 savi ngs 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 TECHNICIAN’S NOTES
Throughout production of the “FX” series transceivers, the technicians here
at Ramsey have been speak ing with customers, making repairs,
experimenting, and compiling notes on the FX-146. These notes, and the
circuit overview and theory of operation sections of your FX-146 manual,
provide extensive information on the inner workings of the FX-146. Should a
nasty gremlin jump into your trusty new FX-146, this information will help
lead your foray into troubleshooting.
Several voltages and testpoints are given throughout this guide. Keep in
mind that, due to differences in test equipment, power supply voltage, etc.,
your readings may vary slightly. Any voltage within 20% or so should be
considered ok. It may also be difficult to lead you to a specific component or
fault right off.
Now clear off that workbench, lock the doors, put up the “do not disturb”
sign, and let’s get started!
Preliminary Checks: (Many times these first few checks will solve the
problem.)
1. Proper DC voltages . (+13.8VDC, +8V, +5V, +8T, +8R)
2. Solder connections. All joints should be clean, shiny, and solid. (You
won’t need a magnifying glass. If a connection is suspect, reflow the
solder.) Also, check for stray solder shorts or bridges.
3. Easy to confuse items. Now let’s see, was that a 10K ohm resistor
or 1K ohm? Some of those color bands look quite similar to tired
eyes. Let another pair of eyes check your work.
4. Component lead length. VERY IMPORTANT! Make sure all
component leads are as short as possible. In other words, pull the
leads through the board until the component body rests on the
board. The hand wound coils of buss wire should not touch the
board! (One exception - obviously)
5. Make sure only one channel is activated at a time. A diode installed
backwards in another channel can turn on two channels at once!
Your voltmeter should indicate voltage on only one bus wire at a
time. This is true for the offsets too.
FX 146 • 8
6. Reread those sections of the manual where you feel the possible
fault could be. A thorough understanding of each circuit just may
FX-146 • 139
good 50 ohm load. Keep these key -down tests as brief as possible.
? TX52. If you are observing at least 4 watts of RF output, transmitter
tuneup is completed. Spread coils L13 and L16 on the main board and
L12 and L22 on the low pass board for maximum RF output. These coils
are purposefully wound with a little too much inductance, so that they
can be easily "peaked" by some spreading. This is probably one of the
most important steps to get the most RF out of your rig.
? TX53. Adjust Modulation control R46 by listening on another receiver or
scanner and simply adjust for best sounding audio. See Test Procedure,
Step 8, regarding FM De viation.
? Remember that indicated RF output also depends on the accuracy of the
wattmeter and correct DC supply voltage. Our lab measurements
consistently show 4 to 5 watts or better. If your application demands
significantly more RF output, your FX-146 transceiver will drive the
Ramsey PA-146 booster amp (factory assembled with recei ver pre-amp)
to its maximum rated outputs in the 35 to 40 watt range.
? TX54. Replace the dummy load with a well designed 2 Meter antenna
and start enjoying the FM transceiver that you built yourself!
IMPORTANT:
It is your responsibility to know what band privileges are granted by
your Amateur Radio License and how to program the frequency
synthesizer correctly within the 144.00 to 148.00 MHz operating range
of the 2 Meter Amateur Band. A proper license is required for
transmitting in this band. Other FCC licensing is required for operation
of this equipment on frequencies outside the Amateur Band. It is illegal
for licensed amateurs or other persons to transmit on frequencies for
which they are not properly licensed.
RAMSEY
ELECTRONICS, INC.
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 publicatio ns. A
convenient new book featuring easy-to-find components and clear
explanations is Building Power Supplies (Radio Shack 276-5025.)
FX 146 • 138
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 bec ome 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 distributors 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.
This completes the assembly of the low pass filter PC board. Inspect the
board to be sure all leads on the bare side of the boa rd are trimmed neatly
and that the coils do not short against the PC board ground plane.
? TX45. Exactly when to install the SO-239 antenna RF connector is left to
your discretion. If you are using your own case, you must now "wing it"
on your own, observing the way we are mounting the connector to our
case. If you are using the Ramsey CFX case set, mount the SO-239 to
the rear panel as part of this assembly operation. Use the two screws
and four nuts supplied and consult the illustration as needed. The flange
of the connector sits on the outside of the rear panel. Mount the
connector with one set of nuts, then mount the low pass filter PC board
using the other two nuts. Solder the connector center pin to the board.
? TX46. Line up the two ground wires and C63, the .01 uf coupling
capacitor, on the low pass filter board with the mating holes on the main
FX PC board. Allow the low pass board to stand about 1/8" above the
main FX board and at a neat right angle. Solder the leads to the main
FX board, be careful so as to not loosen the solder joints on the little
board from too much heat when soldering - if you do, just retouch the
solder joints again, it's no big deal!
TRANSMITTER COMPLETION AND TUNEUP
Do not proceed with the following until all of the previous steps have been
completed successfully. You now have a somewhat fragile assembly, the
rear panel being held to the main PC board with only three wires, please be
careful during the next few steps.
? TX47. Install L10, an orange wire coil that appears to have 5 turns when
viewed from the top.
? TX48. Install R32, the remaining 1/2-watt 82 ohm resistor. (Larger body:
gray-red-black).
? TX49. Install RF choke L9, reviewing Section "TC" and Step TX15, if
necessary.
? TX50. Connect the following to your transceiver:
? 50-ohm dummy load
? VHF RF wattmeter or voltmeter connected to R115, the stand up
resistor test point on the low pass filter board.
? DC 12 volts power
? TX51. Press (key) the transmit button and alternately adjust C84 and
C74 with a non-metallic alignment tool for maximum RF output indicated
on the meter. If you are using a voltmeter con nected to the resistor test
point, you will typically see about 12 to 15 volts when connected to a
FX 146 • 10
FX-146 • 137
main PC board.
Quantity RS Part No. Description 1992 Price ($)
1 270-272/74 Deluxe Project Enclosure 8.79 or 10.79
#4-40 Screw
SO-239 Female
Case Panel
#4-40 nuts
Spacer nut
1
02
C7
Ground Jumper
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 • 136
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 pa nel
? 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 bo ard 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 PROCE DURE:
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
the lead preventing a good solder connection, you may wish to slightly
scrape away this coating on some parts.
? TX35. Install R11 9a, 1K (brown-black-red).
? TX36. Install D26, 1N914/1N4148 diode, observe correct placement of
the cathode band.
? TX37. Install C71, 39 pf.
? TX38. Install C19, 56 pf.
? TX39. Install C72, 39 pf.
? TX40. Install L12, the 2 1/2 turn coil prepared in stage TC. Insertion will
require you to spread the windings slightly to fit the holes. When
mounting these coils, do not allow the wire spirals to contact the PC
board ground plane area under them. The coil must sit slightly above the
board and not short against it.
? TX41. Install L22, another 2 1/2 turn previously wound. Again, be sure
you don't allow the coil to short against the ground area.
? TX42. Fabricate R115. Locate a 1K resistor (brown-black-red). Cut on e
Test point loop
Resistor
PC Board
lead to a length of 1/4" and bend it into a small loop as shown. Carefully
hold it straight while soldering it to the board. This loop will provide a
handy point to attach a meter
probe.
? TX43. Install C63. Locate a .01
uf capacitor, bend out its leads
away from the body and insert
one lead into the PC board and
solder. Its other lead will
connect to the main PC board
later.
? TX44. Locate two scrap component leads at least 1/2" long. Solder
each lead to the PC board as shown. These leads will also attach to the
FX 146 • 12
FX-146 • 135
? TX26: C58, the last .1 uf capacitor.
? TX27: C59, .001 uf.
? TX28: L13, 1.5 turn hand -wound coil. Review "TC" and TX16.
? TX29 C73, 18 pf.
? TX30: C55, .01 uf.
? TX31: C74, 35 pf trimmer.
? TX32: C84, 35 pf trimmer.
? TX33: C64, .001 uf.
? TX34: L8, 2.2 uH molded inductor (2 red, 1 gold and 1 black stripe).
At this point, every single main PC board component has been installed
except for L10, R32 and L9, which apply power to the RF output transistors
(driver Q9, final Q8). DO NOT INSTALL these parts unt il instructed to do so
during the Transmitter Completion and Tuneup procedure.
Stage TX: FINAL PROGRESS CHECK:
1. Double check component selection for Steps TX.
2. Use bright light and magnifier to go over entire board to check for
missed connections or solder bridges. If you suspect a solder bridge,
simple review the X-ray illustrations to see whether the points in
question are indeed tied together.
3. Carefully check entire board for:
A. Loose bits of wire lodged among connections or components on
either side of board.
B. Excess wire lengths which may not have been nipped and are now
bent flat, probably against another connection.
BUILDING THE LOW PASS FILTER PC BOARD:
The assembly of the low pass filter PC board is quite different from the way in
which you have assembled the main FX transceiver board. Component parts
are mounted on the circuit trace/solder side of the board! The reason for this is
that the board mounts against the output connector - and it would be very
difficult to solder the connector center pin after the board is mounted to it.
You'll see why as you finish building your rig.
When installing parts, insert the component on to the PC board from the
solder side, the leads will extend out through the bare side of the board with
no traces. The part is then soldered on the solder side and the leads trimmed
away flush on the other side. When soldering the disc caps, be sure that their
leads are properly soldered, sometimes the body insulating material will coat
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 • 134
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
8. While speaking in the microphone, adjust modulation level (R46) for the
best sounding speech. "Best" is not necessarily the maximum: see the
following note. NOTE: R46 adjusts the FM deviation of the transmitted
frequency. Deviation is carrier frequency swing in step with voice
modulation. If you "over-deviate," your signal will not be stronger.
Instead, the speech will become distorted and "splash" over to adjacent
channels. Deviation is a very important adjustment: "best sounding
speech" will usually result in the proper 5KHz deviation used on VHF
FM.
9. Disconnect power and proceed with completing the transmitter section
(Steps TX15, etc.)
IMPORTANT: If you do not achieve the test results discussed ab ove, there
is no point in doing more work on the transmitter section until the problem is
solved. If you are not able to transmit at least within the same room and
receive on any desired frequency, finishing the transmitter is not going to fix
the problem.
CONTINUE TRANSMITTER ASSEMBLY:
? TX15. Install RF choke L19 (prepared in Stage TC). Notice that the
holes are diagonal from each other. If the choke was wound correctly,
L19 will line up nicely as illustrated.
? TX16. Coil L16 was also prepared in Stage TC. Insertion may stretch the
windings very slightly. Gently press L16 in as close to he top of the
board as possible, leaving about 1/8" clearance. The coil windings must
not, of course, touch the solder plane.
FX 146 • 14
? TX17. Install C61, .001 uf.
? TX18. Install C66, 3.9 pf.
? TX19, Install C79, also 3.9 pf.
? TX20. Install C78, 22 pf.
? TX21. Referring to step TX1 6 and Stage TC as needed, install L15, the
other 5/16" 2.5 turn coil.
? TX22. Install L18, a .33 uh inductor with axial leads. (L18 looks like a
resistor body with wire wrapped around it and is marked by 2 orange
dots.)
? TX23. Install R45, 82 ohm (gray -red-black), R45 is larger than the other
resistors in your kit, it is a 1/2 Watt size resistor.
? TX24. Install L14, .015 uh, small pre-wound 1/8" 1.5 turn coil.
? TX25. Install C60, 220 uf electrolytic, observe polarity.
FX-146 • 133
However, DO NOT INSTALL L9, R32 or L10 UNTIL AFTER ALIGNMENT
HAS BEEN COMPLETED. Whether you test now or later depends on
how anxious you are to see (and hear) the results of all your hard work.
If you are still awaiting your ham license, you can test the FM
modulation of buffer stage Q10 and also enjoy your receiver fully. Be
aware, however, that the buffer stage, even with no antenna connected
to it, has a transmitting range of about 100 feet, even through walls and
obstacles.
TRANSCEIVER PLL ALIGNMENT (May also be done before Step TX35)
Our goal in this test is to verify speech amplifier operation (U4), actual FM
modulation of a low-level RF signal (Q10), and correct operation of the PLL
Frequency Synthesizer in Transmit mode. If an antenna is connected for this
test, it will affect receiver operation only. The "antenna" for the 10 milliwatt
output consists of of the lead lengths and circuit-board traces associated
with C76 and C82.
TEST PROCEDURE:
1. Make sure work area is cleaned up and that the PC board is checked for
wire scraps lodged between connections, etc.
2. Set transceiver frequency to 146.52 MHz Simplex.
3. Obtain or make a non -metallic alignment blade capable of turning the
slug in L7 and also turning trimmer C81.
4. Connect speaker, microphone, ant enna and 12-15 volts DC. (Antenna
will serve receive function only.)
5. Connect a digital voltmeter (DVM) of known accuracy to TP 1 (red + lead
to the test point, and black lead to ground). Set the meter to the lowest
DC range that will handle up to 7 or 8 volts. A digital voltmeter is used
for this procedure because it has the required high input impedance.
6. With the transceiver po wer turned on, press the microphone button and
adjust L7 for a reading of 1.6 VDC at TP1.
7. A precision adjustment of C81 requires either a frequency counter
connected to TP2 or a digitally accurate VHF receiver tuned to 146.52
MHz. With the microphone keyed (button pressed), C81 is adjusted for
exactly 146.52 MHz on your Ramsey frequency counter or a zero-beat
146.52 MHz signal on a digitally accurate monitoring receiver. If you
cannot tune C81 low enough, install C80, 39 pf (this places more
capacity across C81). An adequate initial adjustment of C81 can be
made by listening to your signal on any VHF FM receiver and carefully
adjusting C81 for the clearest-sounding signal. Or: adjust C81 for the
best reception of a transmitted signal of known accuracy. This might be
all that you'll ever need to do, but it is recommended that you make the
precise adjustment when possible.
1. PRIMARY CONNECTIONS:
PWR (near L20): +12 -15 volts DC from S1.
GROUND: - DC from battery or power supply.
SPEAKER: both connec tions 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 fo r 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 • 132
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 resistance 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.
B. Unpack and study the design of the chip, noting both ends are metallic.
C. Lightly pre-tin both PC board points.
D. Holding C75 in place across the two tinned points with tweezers, gently
touch one junction with the soldering tip. The connection should solder
easily.
E. Solder the other end and touch up the first one if necessary.
Identify and install the following components:
? TX4: C56, 10 pf.
? TX5: R29, 100 ohms (brown-black-brown).
? TX6. L11, miniature .33 uh. inductor (small green body, two orange
stripes)
? TX7. C44, .001 uf.
? TX8: C76, 15 pf.
? TX9: C82, 10 pf.
? TX10: R36, 10K (brown -black-orange).
? TX11: R110, 10K (brow n-black-
orange).
? TX12: R34, 270 ohms (red -violet-
brown).
? TX13: C97, .01 uf.
? TX14: Install Q10, NE021, the
Transmit Buffer transistor. It installs
in the same way as Q3, which was installed in step DR19. Go back and
re-read the steps required when installing a transistor of this style. You
must make sure it is seated snugly against the board before soldering.
At this point, all transceiving functions except final transmitter output power
may be tested and aligned. Q10 has plenty of RF output (10 milliwatts) for a
signal that can be heard in a nearby receiver or scanner. You may test and
align the transceiver now or do so after installing the remaining transmitter
parts.
FX 146 • 16
FX-146 • 131
IMPORTANT:
DO NOT install any parts near Q8 until after Q8 has been installed in accord
with the explicit directions in Step TX2. If you fail to observe this caution, it
will be virtually impossible to perform the installation of Q8 correctly.
DO NOT INSTALL L9, R32 or L10 UNTIL AFTER ALIGNMENT HAS BEEN
COMPLETED.
C75 is a SMT (surface-mount -technology) "chip" capacitor and is the only
part installed on the SOLDER SIDE (bottom) of the board.
? TX1. Install Q9, RF NPN type 2N3866. Let it rest flush on the round
bare area of the board. The holes match the pins, so the tab will point
exactly as illustrated.
? TX2a. RF Final transistor Q8 (MRF237 or SD1127) is also installed
completely flush on the board, with the tab oriented toward L9. The
case of Q8 is common to the emitter. Be sure the case stays completely
flat against the top ground plane when soldering the 3 points.
READ CAREF ULLY: The following procedure lets the top groundplane serve
as the heatsink for the RF final output transistor. Do not be hesitant in
making a smooth solder bond between Q8's case and the board. An ordinary
soldering pencil tip applied to both the case an d the groundplane at the
same time will NOT damage Q8. On the other hand, the lack of a good
heatsink bond WILL destroy Q8 when transmitting. This procedure is
INTENDED by the manufacturer.
? TX2b. Now, using only your regular soldering pen and NOT a solderi ng
"gun," solder the rim of Q8 directly to the top ground plane, starting at
the square tab. Use enough solder for thorough bonding.
? TX3
A. Prepare the following tools for installing SMT chip capacitor C75:
? Tweezers
? Magnifier (if needed)
? Low wattage, clean soldering tip.
VHF PACKET DATA OPERATION
Your FM transceiver was planned and designed to accommodate easy and
reliable VHF packet radio operat ion.
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 plu g (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:
Location of C75
C75
FX 146 • 130
FX-146 • 17
RAMSEY FX-SERIES FM TRANSCEIVER
(With emphasis on the PLL and VCO)
MC13135
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 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
alignment in transmit mode as soon as this stage is built. Operating bias is
supplied by the PLL lock detect voltage from U5B through R110. If the PLL
unlocks, Q10 does not operate, preventing the radiation of out -of-band
signals.
The 2N3866 Driver, Q9, amplifies the output of Q10 to drive Q8 to its full
rated output. Q8, the popular MRF237 or its equivalent, has physical
characteristics that the builder should understand. Many RF transistors of
this style have the Collector lead common to the case. Through
sophisticated insulati ng technology, the Emitter lead is common to the case.
There is significantly better gain because there is no emitter lead lengt h to
speak of. This relatively small transistor package can handle large power
dissipation IF the case is properly soldered to the groundplane of the PC
board as detailed in the assembly instructions. The transistor is fully intended
by the manufacturer to be heat-sunk in this manner: don't worry about
soldering heat damaging the device.
An unusual part is C75, a SMT "chip capacitor". It is installed on the solder
side of the board, and its leadless design is what allows Q9 to deliver such
exceptional gain.
DO NOT install any transmitter parts without at least reading over the
assembly details first and the reasons for the sequence that we have
recommended. The PIN T-R diodes D7, D6 and D2 are discussed in section
DR. In brief review, D7 passes RF to J3 during transmit while D2 and D6
protect the receiver RF input. The antenna input is designed for a 50 ohm
resonant antenna. C84 and C74 are tuned for maximum RF output (3 to 5
watts). These adjustments are part of final transmitter alignment.
Maximum RF output depends critically on following the coil winding
instructions EXACTLY in Stage "TC".
Stage TX: TRANSMITTER SECTION ASSEMBLY:
Install the components in the order recommended and DO NOT under any
circumstances connect DC power to the unit unless instructed to do so at a
particular point. The following assembly steps presume that Stage "TC" (RF
coil and choke preparation) was done. Refer to "TC" if you have any
question on these parts, which also may be built up as you proceed.
FX 146 • 18
FX-146 • 129
Stage TX: Transmitter, Buffer and Final Amplifier
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 over view of FXseries technical information provided in the building stages. However, we'll
still follow the same stage-by-stage des ignations 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 regulat ed 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 gr ound 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 • 128
FX-146 • 19
6. Press the microphone button: the TX LED should light, and the
receiver should be silenced.
2.5 TURN
1.5 TURN
7. Touch a wire from ground to pin 3 of the Packet I/O jack. Do the
same with any resistor that is 47K or lower. Either way, you should
get the same results as in Step 6.
8. Disconnect the DC Power.
OPTIONAL:
Interested builders might wish to verify microphone amplifier operation at PC
board point "PL" before proceeding, but such a test is not essential at this
point. Simply connect a utility test amp to "PL", pres s the mike button and
talk!
Assembly Stage "TC": Transmitter Coil & RF Choke Preparation
A few parts need handmade preparation before installation in the transmitter
RF stages of your transceiver. We recommend that you get them ready for
installation before wiring the Driver and Final stages. If you prefer to proceed
with those stages, winding coils as you go, that's fine, too, as long as you
realize that all coil making details are provided in this section.
The wire used for L9 and L19 is the smaller gauge tinned "bus" wire supplied
with your kit. If you mess up, you can get a whole 50' spool of it from Radio
Shack (278 -1341).
FX 146 • 20
? TC1: RF CHOKES (two identical units required for L9 and L19):
Examine the two cylindrical ferrite cores provided in the kit. Notice that
there are six holes at either end of these cylinder shaped units,
arranged in two groups of three. Cut 6" of bus wire and following the
FX-146 • 127
background noise is audible.
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 convert s 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 45 5 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 adj ustment. 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 Prea mplifier: 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 gro und
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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 caus es 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 output 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 rec eive,
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
during transmit.
? M35: R107, near Y1, 10K (brown-black-orange).
? M36: D22, near VR1, type 1N914 or 1N4148. Orient the banded end
correctly. (+8T through R107 and D22 turns on Q6 to mute the audio
amp IC during transmit).
? M37: C62, near R113, .001 uf.
? M38: Diode D5, near R35, type 1N914 or 1N4148.
? M39: R31, near D5, 47K (yellow-violet-orange).
? M40: R33, also 47K (yellow -violet-orange).
? M41: R70, near diode matrix, 1K (brown-black-red).
? M42: Install the LED transmit indicator, D17, correctly identify the anode
side lead which is the longer of the two. Install the LED with full lead
length extending above board so that the LED can be positioned in the
front panel hole.
? M43a. Referring back to Section A if needed, prepare two 11" wires ( or
11" of 2 conductor wire) and solder one end of each to IN and GND
(MIC) between C86 and U1.
? M43b. Study microphone jack J4 and the above drawing. Solder the
other two wire ends to the jack lugs as shown.
STAGE M PROGRESS TEST
1. Check the PC board for wire scraps, untrimmed leads, etc.
2. Connect an ICOM compatible speaker -microphone to the Mic jack.
3. Connect DC power, antenna and speaker.
4. Turn the power switch 'ON' and verify that receiver still works
properly.
5. Select a steady signal or turn the squelch control so that the
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