4-19.5 MHz
SHORTWAVE RADIO
Ramsey Electronics Model No. SR2
Have you ever wanted to get into the fascinating world of radio?
The Ramsey SR2 is a fine performer that will bring in the world
using just a few feet of wire as an antenna! Folks of all ages
have successfully built and enjoyed this easy and fun kit.
• Enjoy hours of fascinating international listening using just a simple
indoor wire antenna
• Select portions of the 4 to 19.5 MHz shortwave band, easily re-tuned at
any time
• Smooth varactor diode tuning
• Excellent sensitivity and selectivity
• Front panel Volume and Tuning controls
• Multi-stage audio amplifier for room filling volume
• Well designed superhetrodyne circuit is easy to build, makes a nice
one-evening project
• Ideal scout, school, or club project
• Clear, concise step-by-step instructions carefully guide you to a
finished kit that not only works - but you’ll also learn too!
• Runs on a standard 9 volt battery
• Add our matching case and knob set for a finished ‘pro’ look
PARTIAL LIST OF AVAILABLE KITS
RAMSEY TRANSMITTER KITS
• FM10A FM Stereo Transmitter
• FM100B Professional Synthesized FM Stereo Broadcaster
• 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
• SS70A Speech Scrambler
• TT1 Telephone Recorder
• SP1 Speakerphone
• MD3 Microwave Motion Detector
• PH10 Peak hold Meter
• LC1 Inductance-Capacitance Meter
RAMSEY AMATEUR RADIO KITS
• DDF1 DopplerDirection Finder
• HR Series HF All Mode Receivers
• QRP Series HF CW Transmitters
• CPO3 Code Practice Oscillator
• VLF1 Low Bander Low Frequency SWL Converter
• 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.
4-19.5MHz SHORTWAVE RADIO INSTRUCTION MANUAL
Ramsey Electronics publication No. MSR2 Revision 1.4
First printing: January 2001
COPYRIGHT
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.
2001 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Victor, New York
SR2 – 2
Ramsey Publication No. MSR2
Manual Price Only: $5.00
KIT ASSEMBLY
AND INSTRUCTION MANUAL FOR
4-19.5MHz
SHORTWAVE RADIO
TABLE OF CONTENTS
Introduction to the SR2 ........................................ 4
What You Can Expect to Hear .............................4
Shortwave Listening as a Hobby .........................5
Circuit Description ................................................ 6
Parts Layout Diagram .......................................... 8
Block Diagram ..................................................... 9
Parts List .............................................................. 10
Assembly Instructions .......................................... 12
Schematic Diagram ............................................. 14
Shortwave Antenna Ideas .................................... 20
Initial Testing and Adjustment ............................. 21
Troubleshooting Tips ........................................... 23
Ramsey Kit Warranty ........................................... 27
SR2 – 3
INTRODUCTION TO THE SR2
The SR2 is a single-conversion superheterodyne receiver designed
specifically for listening to AM broadcasting stations in the range of 4 to 19.5
MHz. Because of this "superhet" design, your favorite foreign broadcasting
services will come in loud and clear, with pleasing audio sound quality, with
a minimum of overload, frequency drift or heterodyne whistles. Because of
this broadcast oriented design, other shortwave signals such as Morse code
(CW), single-sideband (SSB) voice communications and some Teletype
signals will usually sound like garbled hisses. On the other hand, similarly
inexpensive receivers designed for CW and SSB can give only marginal
performance in receiving broadcast stations due to the lack of
superheterodyne design. For example, our popular Ramsey directconversion receivers for the 40,30 and 20 Meter Amateur bands will also
pick up AM broadcast stations, but you'll mainly hear their strong AM
"carrier" signal due to the lack of the superheterodyne circuitry. Even if such
a carrier is tuned to a "null," listening fidelity is less than desirable.
WHAT YOU CAN EXPECT TO HEAR
First, let's take a look at what is POSSIBLE to hear on your SR2. The
following are the international shortwave broadcasting bands within its
tuning range:
4.750-5.060 MHz. (Lower power, regional "tropical" broadcasting)
5.950-6.200 MHz (Late evening)
7.100-7.300 MHz. (Late afternoon, early evening) (This band is always
shared with the 7.0-7.3 MHz Amateur Radio Band)
9.500-19.500 MHz. (Always "something" on, 24 hours a day!)
Especially strong signals include these, among others:
SR2 – 4
• BBC London: an intelligent perspective on world affairs
• Radio Canada International: editorial quality similar to BBC
• Radio Moscow: powerful signals, increasingly honest and open
• Voice of America: VOA broadcasts are "aimed" outside the USA, but if
you're in the "path" you'll hear it loud and clear!
• U.S. Armed Forces Radio-TV "Feed" Service: Master programming
source for U.S. military radio- hear CBS-NBC-ABC-Mutual news all on
the same "channel," plus many other features and spots which give a
feel for how it's going with those in uniform
• Numerous South American stations
• USA religious broadcasting to other continents
You'll easily tune in broadcasts from many other countries as well. As you
become more and more familiar with the world of shortwave broadcasting,
you'll be deciding on your own favorite band.
You will hear a variety of other "interesting" sounds, but just remember that
this receiver is designed for AM only. If a Morse Code signal really sounds
"good," it is because it is being transmitted in AM tone-modulated form, or
perhaps the signal is so close to an AM broadcast carrier that the carrier
acts as a "beat-frequency-oscillator" (BFO). Even though this receiver can
let you tune through several different HAM radio bands, the signals are not
likely to be intelligible. Reception of CW and SSB signals on an AM receiver
requires a BFO. This is not a complicated feature, but it is beyond the
purpose of the SR2. Our companion receivers designed for the HAM bands
will let you tune into these SSB and CW broadcasts.
SHORTWAVE LISTENING AS A HOBBY
Many people worldwide enjoy listening to shortwave broadcasts of all kinds,
and they keep written records of what they hear. Almost every nation on
earth has some sort of shortwave broadcast service, though many are
much more challenging to tune than the powerful signals of Radio Moscow
and the BBC. In addition, these "SWLs" (Shortwave Listeners) listen to HAM
operators, government and commercial stations and even clandestine
operations. Some shortwave listeners enjoy collecting QSL cards from
stations which they have logged. Shortwave listening is, for some, a step
toward getting a HAM radio license. For others, it is a great hobby in itself.
The SR2 Shortwave Receiver is a good introductory receiver for this hobby.
After you decide exactly what kinds of listening are of the most interest to
SR2 – 5
you, you'll be in a better position to choose a more elaborate receiver. While
there are various multi-band portable radios available, you can expect to pay
at least $100 for a receiver offering a significant improvement over your
trusty SR2.
To learn more about this SWL hobby, look for a copy of "Popular
Communications" at newsstands. An inexpensive and interesting general
introduction to all kinds of radio listening is the book, "Shortwave Listening
Guide" by William Barded, Jr. (1987; Radio Shack Catalog Number 62-
1084). This book also includes helpful introductory information about VHF
monitoring, which you can enjoy with the Ramsey FR-146 and AR-1 receiver
kits, as well as HAM radio, CB, antennas, and other topics.
To learn more about Ramsey Electronics HAM radio kits, write for our
complete catalog. (And, be sure to tell us how you're doing with your SR2
Receiver!) To learn more about the hobby of HAM radio, write ARRL
(American Radio Relay League), 225 Main Street, Newington, CT 06111 or
visit their website: http://www.arrl.org/.
CIRCUIT DESCRIPTION
The following paragraphs describe the circuit operation of the SR-2
Shortwave Receiver kit. Through the use of a simplified block diagram the
basic circuit theory is easy to understand. The full schematic (pg. 14) shows
the details concerning specific operation and component variable
configurations.
Take a moment and examine the circuit block diagram found on page 9. The
simplified signal flow of the block diagram shows the basic sections of the
receiver. The corresponding components are noted under each main block
and can be cross referenced to the schematic
The start of our circuit begins with the Antenna. RF Signals (Fc = carrier
frequency) from the Antenna are applied to the RF Input and Filtering
allowing only the signals of interest to pass through. The high pass filter
helps eliminate unwanted signals picked up by the antenna improving the
overall reception quality of the radio.
After the input signal is filtered, it moves to the Mixer stage. Notice on the
diagram that there are two inputs to the mixer. We have discussed one of
these input signals coming into the mixer but not the other as of yet. Drop
down to the Local Oscillator block. The local oscillator (LO for short) acts as
your tuning control for what frequencies you can receive by generating a
signal on the board close in value to that which will be used by the mixer.
There is a direct relationship between the generated frequency of the local
oscillator (LO) and the exact receive frequency (Fc) you want to listen to.
This will become clear when we finish discussing the block diagram.
The LO section is a Colpitts oscillator that takes advantage of smooth
SR2 – 6
varactor diode tuning. The varactor (D3) forms an L/C (Inductor/Capacitor)
tank circuit with T3. Increasing the voltage on the varactor diode with R21
(Tuning Pot) increases the capacitance of D3 thus increasing the frequency
output of the LO section.
Now that we know the two signals coming into the Mixer stage, both the Fc
(receive carrier frequency) and the LO (generated local oscillator), we can
better cover its operation. The mixer takes these input signals and performs
a few very basic operations. The technical explanation of how the mixer
combines these signals through Fourier Series is interesting but very drawn
out. The point of using the block diagram, however, is to simplify matters.
Therefore, the function of the mixer is to obtain the ‘product’ and the ‘sum’ of
the input signals. This means you take the input signals and merely ‘add’
and ‘subtract’ their values to determine what you get on the output. The
general formulas to use are quite simply, ‘Fc + LO = Mixer Output’ and ‘Fc –
LO = Mixer Output’.
The realistic output of the mixer stage unfortunately has other signals
besides the ones we want. This brings us to the next stage, Intermediate
Frequency Filtering. An Intermediate Frequency (IF) is a signal somewhere
between the RF signal Fc we started with and the final audio message we
are trying to get. The desired IF we are dealing with is a fixed number, such
as 455 kHz. As long as the proper relationship between Fc and the LO
exists, the IF value will stay constant. Due to the fact that the IF frequency
stays the same all the time, the Intermediate Frequency Filter can be very
narrow. The filter will remove any other signals coming from the mixer that
are not in the proper pass band and yield a clean signal for further
processing.
The next stage is an Amplifier with an adjustable gain feedback loop. The
gain control is dependant on the amount of signal being received (this
Automatic Gain Control ‘AGC’ will be covered in a moment). The amplifier
boosts the signal level of the incoming IF and gives us a stronger signal to
work with.
After the amplifier stage is another Intermediate Frequency Filter. This helps
remove any unwanted residual signals still present and cleans up the
amplified IF for a high quality signal.
At this point the audio signal we are trying to obtain is riding on the IF signal.
The Demodulator circuit finally extracts the message from the IF through a
process called envelope detection. Now that we have our message back in
the audio realm, it is directed through the audio circuitry to the speaker
output.
Wait, there are still a few sections we have not discussed!
The demodulated audio branches off before the audio circuitry and is used
to perform some useful functions. The RSSI LED, Received Signal Strength
Indicator Light Emitting Diode, gives us a general signal level feature. The
stronger the signal we receive, the brighter the LED will glow. This is great
for help pulling in those weak transglobal transmitter signals. The gain of the
SR2 – 7
RSSI circuit is controlled by the value the feedback resistor R17. If you are
commonly using a small antenna and listening to weak signals, increase the
value of R17 to customize the response indication of D2, the signal strength
LED.
The final stage, and the real secret to the sensitivity of the receiver, is the
Automatic Gain Control (AGC). The gain control looks at the amount of
signal level present at the output of the demodulator and varies the amount
of gain the Amplifier has accordingly. If there is a strong signal coming
through the demodulator the AGC circuit lowers the gain of the amplifier. If
the receive signal coming through the demodulator is very weak, the AGC
circuit increases the gain of the amplifier (Q2) allowing us to receive signals
from around the world and listen to them with clarity.
SR2 PARTS LAYOUT DIAGRAM
SR2 – 8
Audio
U2, J2
(Speak er)
D1
Demod
LED
Signal
Strength
D2
SR-2 Block Diagram
AGC
T2
Filter
Frequency
Inte rm e diate
Q2
Amp
T1
Filter
Frequency
Inte rm e diate
Q1
Mixer
U1:A
Automatic Gain Control
RSSI
U1:B
Receive S ign al
Strength Indicator
&
Filterin g
C1,C2,C3
RF Input
J1
Antenna
L1,L2
Local
Osc illator
T3,D3,Q3
C15,C16
R2 1
SR2 – 9
Loading...