Ramsey Electronics SS70A User Manual

SPEECH

SCRAMBLER /

DESCRAMBLER KIT

Ramsey Electronics Model No. SS70A

Communicate in privacy over any audio path! Full duplex
operation so this unit can scramble and descramble at the same
time! E-Z hookup instructions for radio, or scanner.

• Uses “state of the art” digital electronic filtering for superior noise
free sound! Speech inversion type system - similar to SSB.

• Decodes most cordless phones and basic 2-Way radio systems

• Loud, amplified speaker output - no need for an external amp!

• Super clean, low noise audio - excellent audio quality!

• Accepts mike, line, or speaker level inputs.

• Handy phono type input and output connections.

• Operates on 9 to 15 volts DC.

• Super easy hook-up with pushbutton “bypass” mode. Switch from

scramble/descramble to feed through without moving wires!

• Informative manual answers questions on theory, hookups and
uses - enhances resale value, too!

• Add our custom case and Knob set for a finished “Pro” look.

SS70A • 1

RAMSEY TRANSMITTER KITS

• FM100B Professional FM Stereo Transmitter

• FM25B Synthesized Stereo FM Transmitter

• MR6 Model Rocket Tracking Transmitter

• TV6 Television Transmitter

RAMSEY RECEIVER KITS

• FR1 FM Broadcast Receiver

• AR1 Aircraft Band Receiver

• SR2 Shortwave Receiver

• SC1 Shortwave Converter

RAMSEY HOBBY KITS

• SG7 Personal Speed Radar

• SS70A Speech Scrambler

• BS1 “Bullshooter” Digital Voice Storage Unit

• AVS10 Automatic Sequential Video Switcher

• ECG1 Heart Monitor

• WCT20 Cable Wizard Cable Tracer

• LABC1 Lead Acid Battery Charger

• LC1 Inductance-Capacitance Meter

RAMSEY AMATEUR RADIO KITS

• DDF1 Doppler Direction Finder

• HR Series HF All Mode Receivers

• QRP Series HF CW Transmitters

• CW7 CW Keyer

• 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.

SS70A SPEECH SCRAMBLER KIT INSTRUCTION MANUAL

Ramsey Electronics publication No. MSS70A Revision 1.3

First printing: September 1995

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.



1995 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Victor, New York

SS70A • 2

Ramsey Publication No. SS70A

KIT ASSEMBLY

AND INSTRUCTION MANUAL FOR

SPEECH SCRAMBLER /
DESCRAMBLER KIT

TABLE OF CONTENTS

Introduction to the SS70A ............. 4

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

Parts List ....................................... 7

Schematic Diagram ....................... 8

SS70A Assembly instructions ....... 9

Testing the SS70A ....................... 12

Hook-up Configurations ............... 13

Troubleshooting ........................... 16

Parts Layout Diagram .................. 18

Ramsey Kit Warranty ................... 19

Price $5.00

SS70A • 3

RAMSEY ELECTRONICS, INC.

590 Fishers Station Drive

Victor, New York 14564

Phone [phone]

Fax [phone]

www.ramseykits.com

INTRODUCTION

The Ramsey SS70A is a complete two-way speech scrambler/descrambler
with suitable inputs and outputs for scanner, two-way radio, cordless
telephone, or tape recorder operation. It is designed to help the user secure
total privacy for communications or recorded memos. Just as its scrambling,
technically called “speech inversion”, can be decoded by knowledgeable
users of similar equipment, the SS70A in turn can be used experimentally to
descramble some public service communications, cordless phones and other
systems where low cost scrambling is employed.

Similar to the regulations affecting the use of mobile VHF scanners, it is the
responsibility of the user of this equipment to know and observe any
applicable laws regarding the interception and descrambling of transmissions
employing speech inversion.

“Speech inversion” is a process that interchanges high and low speech
frequencies by removing the carrier frequency and transmission of only one
sideband in a communications link. This renders the speech unintelligible
unless received by a device capable of replacing the carrier frequency
exactly. The single inversion scrambling technique used in the SS70A is
adequate to minimize casual eavesdropping or ambulance chasing. Greater
security is possible, using precision audio filters, and by inverting more than
one audio range simultaneously.

SS70A CIRCUIT DESCRIPTION

Radio amateurs will notice some similarity between the SS70A and a basic
sideband transmitter. However, in the speech scrambler’s case, the audio
input is mixed with a local oscillator running right in the audio range (3.3 KHz)
rather than an RF oscillator, and it is precisely that modulation of such a low
frequency that results in speech inversion. Let’s look more closely at what
happens in the circuit. Have a glance at your schematic and follow along.

At the heart of the speech scrambler circuitry is the MX128 full-duplex
frequency inversion scrambler IC. This chip contains a balanced modulator
and several digital audio filters for both transmit and receive audio paths. In
addition, the 3.3 KHz injection frequency is generated within the MX128. J3
provides selection of either a 10.24 MHz or 3.58 MHz crystal.

Notice the similarity between the transmit (TX) and receive (RX) circuit paths.
Both inputs are "limited" by the overload protection diodes D1,2,3, and 4. An
additional "voltage divider" (R1,R3) is used to reduce the RX input level when
speaker level input path is selected. The TX path is designed for microphone
level inputs/outputs.

SS70A • 4

Audio In

A

MPLITUDE

Desired

Mixer

OSC

IN

Filter

Inverted audio

out

Spectral display of audio inputs and
outputs. Sum components are
filtered, difference components are
used.

Filtered

Audio Osc

FREQUENC Y

Sum Difference

The audio input is amplified and filtered by the IC, then "mixed" with the
carrier to produce both the sum and difference frequencies. For example, a
500 Hz input mixed with the 3 KHz carrier will produce signals at both 2500
Hz and 3500 Hz and a 1KHz signal will produce a 2 KHz and 4 KHz result.
The outputs are now low pass filtered to remove the unwanted signals above
3 KHz. Final result; the low 500 Hz and slightly higher 1 KHz inputs produce
2500 Hz and 2 KHz outputs respectively. Voila, inverted audio!

The inverted audio is then amplified by either Q1 or Q2, depending on the
path. On the RX path, J4 jumper position selects either speaker level audio
from the LM-380 2 watt audio amplifier or line level audio output.

Front panel controls include power on/off switch S1, scramble/bypass switch
S2, and RX input level select switch S3 which allows the SS70A to be used
with either line or speaker level inputs. Potentiometer R11 controls audio
level when speaker level output is selected.

SS70A • 5

RAMSEY Learn-As-You-Build KIT ASSEMBLY

There are numerous solder connections on the SS70A printed circuit board.
Therefore, PLEASE take us seriously when we say that good soldering is
essential to the proper operation of your scrambler! Following, are a few
quick tips to make the assembly process a bit more enjoyable.

• Use a 25-50 watt soldering pencil with a clean, sharp tip. Wipe the

tip often on a damp sponge to keep it clean for easier soldering.

• Use only rosin-core solder intended for electronics use.

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

be helpful.

• Keep an eye open for similar components. Hmmm, is that a 1K ohm

or 10K ohm resistor?

• Do your work in stages, taking breaks to check your work. Carefully

brush away wire cuttings so they don't lodge between components.

We have a two-fold "strategy" for the order of the following kit assembly
steps. First, we install parts in physical relationship to each other, so there's
minimal chance of inserting wires into wrong holes. Second, whenever
possible, we install in an order that fits our "Learn-As-You Build" Kit building
philosophy.

For each part, our word "Install" always means these steps:

1. Pick the correct part value to start with.

2. Insert it into the correct PC board location.

3. Orient it correctly, follow the PC board drawing and the written

directions for all parts - especially when there's a right way and a
wrong way to solder it in. (Diode bands, electrolytic capacitor
polarity, transistor shapes, dotted or notched ends of IC's, and so
forth.)

4. Solder all connections unless directed otherwise. Use enough

heat and solder for clean, shiny, completed connections.
Don't be afraid of any pen-style soldering iron having enough
heat to damage a component.

5. Trim or "nip" the excess component lead wire after soldering.

NOTE: Save some of the longer wire scraps nipped from resistors and
capacitors. These will be used to form wire jumpers (JMP1, etc.) to be
soldered in just like parts during these construction steps.

Now, let's get building!

SS70A • 6