Elenco Telephone Bug User Manual
TELEPHONE BUG KIT
MODEL K-35
Assembly and Instruction Manual
Copyright © 2010, 1989 by Elenco®Electronics, Inc. All rights reserved. Revised 2010 REV-L 753235
No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.
Elenco®Electronics, Inc.
PARTS LIST
If you are a student, and any parts are missing or damaged, please see instructor or bookstore.
If you purchased this kit from a distributor, catalog, etc., please contact Elenco®Electronics (address/phone/e-mail
is at the back of this manual) for additional assistance, if needed. DO NOT contact your place of purchase as they
will not be able to help you.
RESISTORS
Qty. Symbol Description Color Code Part #
r 1 R1 Resistor 47Ω 5% 1/4W yellow-violet-black-gold 124700
r 1 R3 Resistor 680Ω 5% 1/4W blue-gray-brown-gold 136800
r 1 R2 Resistor 270kΩ 5% 1/4W red-violet-yellow-gold 162700
CAPACITORS
Qty. Symbol Description Part #
r 1 C2 Trimmer Cap 5-40pF 201088
r 1 C3 Capacitor 47pF (47) 214710
r 1 C1 Capacitor 100pF (101 or 100) 221017
r 1 C4 Capacitor 470pF (471 or 470) 224717
SEMICONDUCTORS
Qty. Symbol Description Part #
r 1 Q1 Transistor 2N3904 323904
r 1 Q2 Transistor MPSA56 320056
MISCELLANEOUS
Qty. Description Part #
r 1 PC Board 517001
r 6” Wire black 22ga Solid 814120
r 6” Wire red 22ga Solid 814220
r 6” Wire green 22ga Solid 814520
r 6” Wire gray 22ga Solid 814820
r 6” Wire enamel 28ga 857220
-1-
Resistor Transistor
Capacitor
Trimmer Cap.
PARTS IDENTIFICATION
IMPORTANT NOTICE
It is illegal to listen to a telephone conversation without the person’s consent. This kit is designed for educational
purposes only. It is meant to teach students and hobbyists the transmitting principle for a cordless telephone.
The manufacturer of this kit cannot be held responsible for any illegal use.
INTRODUCTION
The Telephone Bug is really a miniature FM radio transmitter broadcasting within the 88 to 108MHz (megahertz)
band. It is designed to be wired inside a telephone or the wires leading to the telephone. The voice frequencies
carried by the telephone wires modulate the FM transmitter allowing both sides of the telephone conversation
to be heard on any standard FM radio. Because of the unique circuitry , no battery is needed to operate the
unit. The power is taken from the telephone line.
CIRCUIT OPERATION
Figure 1 is a block diagram of how the Telephone Bug works. It consists of an audio amplifier, modulator, an
RF oscillator and an antenna. We shall look at these basic circuits and examine how they function.
-2-
Audio
Amplifier
Modulator
RF
Oscillator
Antenna
Black Wire
Telephone
Gray Wire
Red Wire
Telephone Lines Input
Green Wire
IDENTIFYING CAPACITOR VALUES
Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or μF (microfarads). Most capacitors will have
their actual value printed on them. Some capacitors may have their value printed in the following manner.
For the No.01234589
Multiply By 1 10 100 1k 10k 100k .01 0.1
Multiplier
IDENTIFYING RESISTOR VALUES
Use the following information as a guide in properly identifying the value of resistors.
BAND 1
1st Digit
Color Digit
Black 0
Brown 1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Gray 8
White 9
BAND 2
2nd Digit
Color Digit
Black 0
Brown 1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Gray 8
White 9
Multiplier
Color Multiplier
Black 1
Brown 10
Red 100
Orange 1,000
Yellow 10,000
Green 100,000
Blue 1,000,000
Silver 0.01
Gold 0.1
Resistance
Tolerance
Color Tolerance
Silver +10%
Gold +
5%
Brown +1%
Red +
2%
Orange +3%
Green +.5%
Blue +
.25%
Violet +.1%
Bands
1 2
Multiplier
Tolerance
Second Digit
First Digit
Multiplier
Tolerance
103K
100V
Maximum
Working Voltage
The value is 10 x 1,000 = 10,000pF or .01μF 100V
The letter M indicates a tolerance of +20%
The letter K indicates a tolerance of +
10%
The letter J indicates a tolerance of +
5%
Note:
The letter “R” may
be used at times to
signify a decimal point; as
in 3R3 = 3.3
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