repeater circuit vox3

Spy Recorder Circuit - Repeater Circuit

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Resistors: 1/4 Watt
R1 = 220 Ohm
R2 = 12K
R3 = 10K
R4 = 22K
R5 = 330K
R6 = 10K
R7 = 56K
R8 = 1 MEG
R9 = 22K
R10 = 1K
R11 = 10K
Capacitors: - Disc Or Electrolytic ( Electrolytic
Shown with +/- )  All Low Voltage
C1 = .05 ( Note: A .047 Can Also Be Used Here )
C2 = 6.8 MFD
C3 = .05 ( Note: A .047 Can Also Be Used Here )
C4 = 470 MFD
C5 = 4.7 MFD
C6 = .001
C7 = .05 ( Note: A .047 Can Also Be Used Here )
C8 = 1 MFD
C9 = .001
C10 = 470 MFD
Q1,  2N3904 - NPN
Q2,  2N3906 - PNP
Q3, Q4,  2N3904 - NPN
A Standard 555 Timer Chip. Place A Jumper Wire Between Pins 6 and 7
D1, D2:
1N4148 Diodes
ON/OFF Switch:
Any, On / Off Switch Will Do - connecting the + side of the 9 volt battery to
the circuit
9.0 Volts D.C. The Negative Side Of The Battery Connects To The On/Off
Switch to ground
Any Relay that has a "MINIMUM" -  of 500 Ohms On It's Coil. I have used
several from 500 Ohms up.
Any 6 volt L.E.D. This is simply an indicator light that cycles on - when a
transmission is being received. Adjust the value of resistor R10 for a brighter
or dimmer L.E.D.. Decrease the value for "BRIGHT" - Increase the value for
When used as a recorder actuator - use a standard male mono jack, along
with a patch cord -  to feed the "Remote" port of your recorder. When used
as a repeater, connect in series with the "Transmit" button of your transmitter
Use a Patch Cord ( 1/8" ) to connect from your receiver "EAR" or external
speaker port at this point
Use a patch cord along with a male mono jack ( 1/8" ) to connect from this
point to the "Mic" input portion of your recorder when using this circuit as a
remote receiver to recorder actuator. When using this circuit as a repeater,
add a resistor from the output of C2 that will feed directly into the modulator
of your transmitter. Start with a 1MEG and then reduce the value until you
have clear audio from your transmitter into it's new frequency.

One of the most interesting request that I had when I was on the road
selling and building surveillance gear was for a unit that would
automatically monitor, and record cell phone traffic. I knew at the time that, that
would be virtually impossible since anyone with knowledge of the cell system at that time and even
today is aware that as a signal becomes weak in one area, when a subject is moving such as in an
automobile, it will switch off to another stronger tower, therefore a new frequency change in any of
hundreds of channels.
Another request that I had, when I contracted one of the small low-powered concealed
crystal controlled bug transmitters was for a repeater that would pick up it's weak signal on it's
operating frequency and then re-transmit that audio on another frequency at a very high power so it
could be received miles away.
Regarding the cell phone monitor request above, and also the request for a
repeater circuit, the VOX3 circuit below came into being. I was told that the subject using his
cell phone was in a fixed location and not moving around, and # 2 the only way I could produce the
repeater was if they supplied me with one of their portable Walkie Talkies set to the frequency they
wanted to monitor. The VOX3 fit the bill for both applications. I modified a standard scanner for the
cell phone frequencies, had a Police Walkie Talkie on hand - and went to work. The VOX3 circuit
was the end result.

spy recorder, repeater circuit
When The Unit Is In Operation, and anything is picked up when used as an automatic recorder, the relay actuates and automatically starts the recorder. When the conversations stop, the relay stops and the recorder stops.
When used as a repeater, the relay feature feeds the mike button circuit rather than a recorder input