Ramsey Electronics FR146 User Manual

2 METER FM

RECEIVER KIT

Ramsey Electronics Model No. FR146

Keep an ear on the local repeater action from your easy chair with this simple and fun to build FM receiver. Tune the entire 2 Meter band or the VHF high Police and Fire band.

• Tunes any 5 MHz portion of the 136 to 175 MHz band.

• Excellent performance, less than 1 uV sensitivity.

• Tuned input, low noise preamp stage.

• True Dual-conversion superhet design with 2 pole

Ceramic High IF and 6 pole Ceramic low IF filters!

• Front Panel Volume, Squelch, and Tuning controls.

• Excellent receiver for weather band, police, fire, etc.

• Informative manual answers questions on theory, hook-

ups, and uses - enhances resale value, too!

• Add our case set for a finished ‘Pro’ look. Cases match

all Ramsey products.

• Clear, concise assembly instruction carefully guides

you to a finished kit that works the FIRST time!

PARTIAL LIST OF AVAILABLE KITS

RAMSEY TRANSMITTER KITS

• FM10A FM Stereo Transmitter

• FM100B Professional FM Transmitter

• FM25B Synthesized FM Stereo Transmitter

• AM25 Synthesized AM Transmitter

• AM1 AM Transmitter

RAMSEY RECEIVER KITS

• FR1 FM Broadcast Receiver

• AR1 Aircraft Band Receiver

• AA7 Active Antenna

• SC1 Shortwave Converter

RAMSEY HOBBY KITS

• SG7 Personal Speed Radar

• SS70 Speech Scrambler

• TT1 Telephone Recorder

• PG13 Plasma Generator

• MD3 Microwave Motion Detector

• TFM3 Tri-Field Meter

• WEB1 Walking Electronic Bug

RAMSEY AMATEUR RADIO KITS

• HR Series HF All Mode Receivers

• QRP Series HF CW Transmitters

• DDF1 Doppler Direction Finder

• CPO3 Code Practice Oscillator

• QRP Power Amplifiers

RAMSEY MINI-KITS Many other kits are available for hobby, school, scouts and just plain FUN. New kits are always under development. Write or call for our free Ramsey catalog.

FR146 2 METER FM RECEIVER KIT INSTRUCTION MANUAL

Ramsey Electronics publication NO. MFR146 Rev. E1

First printing: January 1992

FR146 • 2

Ramsey Publication No. MFR146

Price $5.00

KIT ASSEMBLY

AND INSTRUCTION MANUAL FOR

FR146 2 METER

FM RECEIVER KIT

TABLE OF CONTENTS

ntroduction to the FR146 .............. 4

Circuit Description ......................... 5

Parts List ........................................ 6

Simplified Block Diagram .............. 8

Parts Layout Diagram .................... 9

FR146 Assembly Instructions ........ 10

Schematic Diagram ....................... 12

Testing and Alignment ................... 18

Enclosure Ideas ............................. 20

Troubleshooting Guide .................. 21

Notes for Advanced Users ............ 21

Ramsey Kit Warranty ..................... 23

FR146 • 3

INTRODUCTION TO THE FR146 FM RECEIVER

Most Ramsey kits can be classified as “Skill Level 1”. That means that our kits are intended to be sucessful for first-time kit builders. This FR146 FM Receiver is best regarded as a “Skill Level 2” project (or at least Level 1.46!) and should not be taken lightly, even by experienced, licensed radio amateurs.

Still, this step-by-step manual is written with the beginner in mind, because we are well aware of the fascination that Two Meters and its maze of repeaters holds for newcomers, which means this could be your very first kit project. The same holds true for those who just want to peek in on VHF public service communications without the cost of a scanner. To be honest, we'd like to see first-time builders start out with an easier kit such as the Ramsey HR-40 Forty Meter receiver before assembling the FR146, but we are confident that you can construct the FR146 successfully if you follow this manual carefully and patiently.

This receiver is a good project for amateurs wishing to become more familiar with 2 meter FM before choosing a transceiver, or for those active on 2 who want an inexpensive receiver to take on trips, keep in a briefcase or to watch for band openings.

Before beginning the project or even studying the circuit description, it is worthwhile to develop some prior respect for how much receiver is packed onto the circuit board. The nine semiconductor devices (diodes, transistors and IC chips) give the equivalent of about 30 or more transistors diodes. And, in addition to four inductors, a crystal and two ceramic filters, there are nearly 60 capacitors and resistors. Surely, all that should result in a decent receiver! You could easily spend twice the money plus hours of time trying to gather the equivalent parts from catalogs and still need to make your own circuit board.

BUILDING YOUR FR146 KIT

There are just over 200 solder connections on the FR146 printed circuit board. That means your work could be 99% excellent and you could STILL have 2 or 3 cold solder points or solder bridges. Since this circuit is more sophisticated than a direct-conversion HF receiver or a simple transmitter, a beginner or casual amateur could have a harder time tracing a problem due to a poor solder connection. Therefore, PLEASE take us seriously when we say that good soldering is essential to the proper operation of your receiver!

 Use a 25-watt soldering pencil with a clean, sharp tip.  Use only rosin-core solder intended for electronics use.

FR146 • 4

 Use bright lighting. A magnifying lamp or bench-style magnifier may be

helpful.

 Do your work in stages, taking breaks to check your work.  Carefully brush away wire cuttings so they don't lodge between solder

connections.

FR146 CIRCUIT DESCRIPTION

VHF signals from the antenna are amplified through the tuned input circuit (L1, C3 and L2,C4) by Q1, a microwave bipolar transistor. Q1's output is fed to the input of the SA602 IC, an efficient single-package (8-pin DIP) mixer-product detector-oscillator. The tuneable oscillator section of the SA602 is aligned to operate at 10.7 MHz higher than the signal fed and amplified by Q1. For example, to receive 144-148 MHz signals, the oscillator must tune 154.7 to

158.7 MHz in order for the SA602's mixing capability to produce a steady 10.7 MHz output signal to the rest of the circuit. The oscillator frequency is determined by L3 and its associated capacitors, and varied by the varactor tuning network using D1 and varied by R1.

The output from pin 4 of the SA602 passes through a ceramic 10.7 MHz filter, amplified by transistor Q2 and applied to input pin 18 of U2. Q3 provides AFC (Automatic Frequency Control) by keeping the local oscillator of U1 from drifting away from an incoming signal. This is accomplished by tuning the varactor circuit in the direction opposite the drift.

The MC3359 IC has an internal oscillator controlled by the 10.24 MHz crystal. The 10.24 MHz signal is mixed with the 10.7 MHz input from U1 to convert down to the low IF of 450 KHz. The 450 KHz IF is filtered by FL2 and then amplified by a limiting amplifier in U2. Audio demodulation takes place in the quadrature detector, with L4 adjusting the detector.

The audio modulation is detected in U2, and the background noise is used to control the squelch. U3 amplifies the audio output from pin 10 of U2 to a practical level for speaker or headphone operation. Pin 16 of U2 will ground the input of U3 when the squelch is closed.

L4, a 450 KHz IF coil, permits adjustment of the 90-degree voltage-current phasing ("quadrature") of FL2's output to the FM detector demodulator (pin 8 of the MC3359).

FR146 • 5

PARTS LIST

Inductors

 2 small 1 1/2 turn coils (L1,L2)  1 slug-tuned 3 1/2 turn coil [orange color] (L3)  1 shielded transformer coil [marked LB 53303] (L4)

Semiconductors and IC's

 1 2SC2498 or 2SC2570A transistor (Q1)  3 2N3904 transistor (Q2,Q3,Q4)  1 SA602 8-pin IC (U1)  1 MC3359 18-pin FM receiver IC (U2)  1 LM386 8-pin audio amplifier IC (U3)  1 Varactor diode, BB505 [orange body marked BB505] (D1)  1 1N4148 signal diode (D2)

Special Components

 1 10.24 MHz Crystal (Y1)  1 10.7 MHz ceramic filter [brown, molded, 3 leads] (FL1)  1 450 KHz ceramic filter [black, square] (FL2)

Fixed Resistors

 1 2 ohm [red-black-gold] (R22)  3 270 ohm [red-violet-brown] (R6,9,20)  1 470 ohm [yellow-violet-brown] (R5)  2 1K ohm [brown-black-red] (R11,12)  3 10K ohm [brown-black-orange] (R7,17,19)  1 18K ohm [brown-gray-orange] (R18)  1 33K ohm [orange-orange-orange] (R14)  4 47K ohm [yellow-violet-orange] (R4,8,13,21)  1 100K ohm [brown-black-yellow] (R16)  1 470K ohm [yellow-violet-yellow] (R15)  1 1 megohm [brown-black-green] (R10)

Capacitors

 1 8.2 pF (C12)  2 10 pF (C2,5)  2 15 pF (C9,10)  1 22 pF (C19)  2 56 pF (C3,4)  3 100 pF [marked 100, 101, or 101K] (C1,6,22)  1 220 pF [marked 220 or 221] (C18)  7 .001 uF [marked .001 or 102 or 1 nF] (C7,8,11,20,23,24,25)  8 .01 uF [marked .01 or 103 or 10 nF] (C13,16,17,21,26,28,29,31)  1 .1 uF [marked .1 or 104] (C34)  1 1.0 uF electrolytic (C27)

FR146 • 6

 3 4.7 or 10 uF electrolytic (C15,30,36)  4 100 to 220 uF electrolytic (C14,32,33,35)

Controls and Hardware

 1 Printed circuit board  3 10K ohm potentiometer (R1,R2,R3)  1 DPDT push switch (S1)  1 PC mount RCA jack (J1)  1 PC mount subminiature speaker jack (J2)  1 9-volt battery bracket  1 9-volt battery snap-on clip

REQUIRED, NOT SUPPLIED

 1 9-volt alkaline battery  1 VHF antenna with cable terminated in RCA-style plug or adapter  1 Speaker or headphones

NOTE CONCERNING THE AUDIO OUTPUT JACK

Your receiver kit is supplied with a standard subminiature 2.5 mm (3/32") audio output jack, which mates with commonly available earphone plugs and adapters available at Radio Shack, such as 274-290 (plug) or 274-327 (adapter for 1/8" mono plug). If you prefer to use another size and style jack, we suggest that you still install the original jack and then wire your own jack in parallel with it rather to rough up the PC board to accommodate your jack.

SEMICONDUCTOR REPLACEMENT DATA

U1 SA602 (Signetics) Contact Ramsey Factory U2 MC3359 (Motorola) ECG860 or SK7731 U3 LM386 (National) available at Radio Shack, other suppliers Q1 2SC2498 ECG10 or SK9139 Q2,3 2N3904 available at Radio Shack, other suppliers D1 BB505 contact Ramsey Factory D2 1N4148 available at Radio Shack, other suppliers

FR146 • 7

FR146 BLOCK DIAGRAM

U2, 3359

SA602

MIXER

FR146 • 8

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