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Telephone Scrambler (ART433E)

An interesting possibility of becoming incognito in a telephone call is to send a signal that can not be understood by someone listening to the recording. One type of interesting equipment for this purpose is the "scrambler".

This article is part of one of my spy books.

It is a circuit that modifies the frequency of the voice before transmitting it through the line, so that it becomes incomprehensible. A decoder must be used in the receiver.

In figure 1 we have a circuit for radio transmission of a scrambled signal.


Figure 1 - A simple scrambler
Figure 1 - A simple scrambler


At reception we take the receiver signal from the receiver and apply it to the identical circuit connected at the input of an amplifier.

In the circuit of figure 2 we have both the transmission and the reception of the signal by telephone.


Figure 2 - Transmission and reception
Figure 2 - Transmission and reception



In order to use the S-key is placed in the confidential position, after making the call with the S-key in the normal position. We should hear a tone from the oscillator indicating the operation of the system. If this happens, the conversation may continue as normal, confidential.



D1, D2, D3 and 04 - Diode1N4148

IC1 - 555 - integrated circuit



R1 - 1k x 1/8 W (brown, black, red)



C1 - 100 nF x 250 V - epoxy or polyester

C2 - 2.2 uF x 63 V - electrolytic

C3 - 47 uF x 10 V - electrolytic



T1, T2 and T3 - Push-pull output transistor type transistor for transistor (1 k x 2/8 ohm with center socket)

B1 - 4.5 V - 3 batteries or battery

S1 - 4 x 2 key