FR-1 • 1
Ramsey Electronics Model No. FR1
Build your own FM Broadcast receiver. Radio covers 70 to 110
Mhz, ideal for tuning in out-of-band FM wireless mikes, ‘bugs’
and other transmitters that exist where ‘others’ can’t find them!
An added feature of the FR1 is its SCA output, which allows
easy connection of SCA decoders - for commercial -free music,
stock quotes, sports, etc.
Typical uses for the FR1 FM radio receiver:
• Tuning in hidden FM wireless mikes and phone bugs
• Hooking up SCA adapters
• Learning how FM receivers operate
• Snooping around for clandestine transmitters
• Just plain ol’ easy listening to the standard FM radio
The Ramsey FR1 FM Broadcast receiver features:
• Runs on 9 volt battery
• Choice of on-board whip antenna or external antenna
• Stable tuning from 70 to 110 Mhz
• Clear, concise step-by-step instructions
• Plenty of speaker volume
• Handy SCA demodulator output
• Lots of helpful hints and hook-ups
FR-1 • 2
RAMSEY TRANSMITTER KITS
• FM100B Professional FM Stereo Transmitter
• FM25B Synthesized Stereo Transmitter
• AM1, AM25 AM Transmitters
• TV6 Television Transmitter
RAMSEY RECEIVER KITS
• FR1 FM Broadcast Receiver
• AR1 Aircraft Band Receiver
• SR2 Shortwave Receiver
• AA7 Active Antenna
• SC1 Shortwave Converter
RAMSEY HOBBY KITS
• SG7 Personal Speed Radar
• SS70A Speech Scrambler
• SP1 Speakerphone
• WCT20 Wizard Cable Tracer
• TFM3 Tri-Field Meter
• LC1 Inductance-Capacitance Meter
• WEB1 Walking Electronic Bug
• ECG1 Heart Monitor
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.
FR1 FM RADIO RECEIVER KIT INSTRUCTION MANUAL
Ramsey Electronics publication No. MFR1 Revision D1
COPYRIGHT
1994 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Victor, New York
14564. All rights reserved. No portion of this publication may be copied or duplicated without the
written permission of Ramsey Electronics, Inc. Printed in the United States of America.
FR-1 • 3
FR1 FM RADIO
RECEIVER KIT
Ramsey Publication No. MFR1
Price $5.00
TABLE OF CONTENTS
Introduction to the FR1 .................. 4
FR1 Circuit Description .................. 5
Parts List ........................................ 6
Building your kit .............................. 8
Testing and Alignment ................. 12
Troubleshooting Tips ................... 14
Other Hook-ups ............................ 15
SCA output ................................... 16
Schematic Diagram ...................... 18
Ramsey Kit Warranty ................... 19
KIT ASSEMBLY
AND INSTRUCTION MANUAL FOR
RAMSEY ELECTRONICS, INC.
590 Fishers Station Drive
Victor, New York 14564
Phone (585) 924-4560
Fax (585) 924-4555
www.ramseykits.com
FR-1 • 4
INTRODUCTION TO THE FR1 FM RADIO RECEIVER
Why you may ask does Ramsey sell a 'plain old FM radio' receiver? No better
person to ask than yourself! The FR1; teaches radio theory, allows you to
tune outside of the standard broadcast band (great for bugs, FM mikes and
other goodies!), has easy hook up for SCA adapters, small size and is just
plain fun.
Your receiver kit is designed to receive wideband FM transmissions typical of
standard FM broadcast stations, wireless mikes, telephone transmitters and
the like. It was not designed for Narrow Band FM transmissions (NBFM) as
you would find on police and fire transmitters, Ramsey offers a complete line
of receivers for those services.
The FR1 demonstrates a whole lot of basic radio theory in one compact,
simple circuit! Separate circuits are 'on-board' for all basic parts of a receiver,
making it easy to visualize every function. The latest in IC circuitry is used
which allows high performance without requiring exotic construction skills.
We think you'll agree that this little radio offers a lot of bang-for- the-buck, so
let's get building!
AUDIO
OUTPUT
SCA
OUTPUT
FM
DETECTOR
CHIP
Q2
U3
FL1
Q1
AFC
L.O.
FR-1 • 5
CIRCUIT DESCRIPTION
FM broadcast signals captured by the whip antenna or from the input jack are
applied to the RF amplifier Q2, a high gain, low noise microwave style
transistor. Signals are amplified about 20 dB, that's 100 times! After being
boosted, these signals are routed to the SA602 mixer-oscillator chip for
conversion down to the 10.7 Mhz Intermediate Frequency (IF). The SA602 is a
very popular chip used in a great variety of receivers from cellular telephones
to satellite receivers, in fact, here at Ramsey, we use it in every receiver kit we
sell! The reason for its popularity is that it contains most of a receivers 'front
end' circuitry on a single, easy to use chip.
Internal to the SA602 is an oscillator tuned by an external tank circuit; C11,12,
L1 and varactor diode D1. A varactor diode acts like a voltage variable
capacitor and the voltage applied across it comes from Tuning pot R12. This IF
signal is an exact reproduction of the desired signal, but at 10.7 Mhz. We then
band-pass filter it with ceramic filter FL-1. The ceramic filter allows only the
desired 10.7 Mhz signal to pass, rejecting any adjacent channel signals.
Transistor Q1 amplifies the IF signal before it is applied to the detector chip
U1.
One of the primary advantages of FM is that the program information
(modulation) is contained in carrier frequency variations and not in amplitude
changes like AM, which would be susceptible to noise and interference. This
means that we can limit or clip the signal, thus removing any noise and not
affecting the desired information. The first section of U1 performs this limiting
function, providing high gain and clipping any amplitude (noise) variations.
FM is detected in the second section using a process known as quadrature
detection. We'll not get into this too deeply because it requires a knowledge of
trigonometry identities - let's just say it extracts the frequency modulated
program information. Capacitor C1 and coil assembly L2 comprise a phase
shift network that is required by the quadrature detector. Demodulated signals
are amplified and sent out through pin 1 to the; volume control, AFC circuitry
and the SCA buffer amp. The AFC circuitry is used to properly keep the
receiver locked on to the tuned in radio station. Resistor R9 and capacitor C17
filter out any audio voltage variations so that only major frequency changes will
shift the tuning voltage to lock the frequency.
Audio signals from the volume control are amplified to speaker levels by U2,
an LM-386 audio amplifier chip. Transistor Q3 provides a buffer stage to
external SCA devices you may connect up to the FR1. SCA units decode
(demodulate, actually) 'hidden' audio and data services transmitted over
standard FM broadcast channels. These services include stock quotes, sports
scores, talk shows and even background music - commercial free!
FR-1 • 6
RAMSEY FR1 FM RADIO RECEIVER KIT PARTS LIST
CERAMIC DISC CAPACITORS:
4 .001 uf disc (marked .001 or 102 or 1 nf) [C4,5,15,27]
12 .01 uf disc (marked .01 or 103 or 10 nf) [C2,3,7,8,16,18,20,21,23,24,
28,29]
1 .1 uf disc (marked .1 or 104) [C25]
1 4.7 or 5 pf disc (marked 5 or 5K) [C1]
2 22 pf disc (marked 22) [C11,12]
2 100 pf disc (marked 100, 101, or 101K) [C6,14]
ELECTROLYTIC CAPACITORS:
4 4.7 or 10 uf [C9,17,22,26]
3 100 to 220 uf [C10,13,19]
RESISTORS AND POTENTIOMETERS:
2 10K ohm potentiometers [R12,13]
1 2 ohm (red-black-gold) [R19]
3 270 ohm (red-violet-brown) [R3,16,17]
1 470 ohm (yellow-violet-brown) [R6]
2 1K resistor (brown-black-red) [R2,18]
1 2.2K ohm (red-red-red) [R10]
2 4.7k ohm (yellow-violet-red) [R1,15]
5 10K resistors (brown-black-orange) [R5,7,8,9,14]
2 47K ohm (yellow-violet-orange) [R4,11]
INDUCTORS AND FREQUENCY COMPONENTS:
1 10.7 Mhz ceramic filter (looks like 3 leaded disc capacitor) [FL1]
1 slug tuned plastic molded coil [L1]
1 10.7 Mhz shielded can style IF transformer [L2]
SEMICONDUCTORS:
1 varactor diode, 33pf (black with green and red bands) [D1]
1 Zener diode, 6.2 volt (gray with black band) [D2]
1 SA602 IC [U3]
1 LM386 IC [U2]
1 ULN2111 IC [U1]
1 2SC2498 or 2SC2570A NPN transistor [Q2]
2 2N3904 NPN transistor [Q1,3]
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