Re: [TSCM-L] {2403} Contact Microphone Detection
James M. Atkinson wrote:
> To detect a contact microphone I pursue two methodologies but
> technical you could say that I am using three methods.
>
> The first method assumes that I are dealing with a piezoelectric
> transducer as opposed to an electromagnetic transducer. As such a
> piezoelectric device can often be found by the use of a very small
> metal detector, and sometimes via the use of a NLJD if the spy is
> foolish enough to use a device that has significant metallic content,
> or which has electronics on board the device.
>
> If you want a realistic test target for his first method, tape
> several metal seamstresses thimbles to one side of a wall, and then
> go to the other size and try to find then with a metal detector. To
> provide a realistic test target for an amplifier take a 1N914 to
> 1N4148 diode and snip the lead down so that they are no more then 1/2
> inch on each side of the glass and the tape them two at a time to one
> side of the wall, and sweep the other side it with an NLJD.
>
> The second method involves using an electric metronome in the room
> that provide a very precise, and very pure tone. I use a small tuned
> loop stick antenna that is resonant at this tone frequency (I use 1
> kHz), and the time between the acoustic sound reaching the antenna
> and the electronic signal being picked up give me an estimated
> distance to target. If I do not care about ranging the device then I
> just let the tone run all the time and sniff for something providing
> a weak electromagnetic signal at the same frequency as the acoustic
> generator. The key is to keep the electronic portion of your signal
> generator well away from your pickup antenna, and by modulating or
> gating the stimulus signal you can only listen for the signal from
> the microphone when the acoustic source is not throwing off an EM
> signal. Remember that an electrical signal moves faster then sound,
> so you can release a ping, and then wait to hear its echo a few uS
> later with no problem (when he EM signal is no longer there). I have
> been doing this for several years with good success and can catch
> most covert contact microphones even behind 8 inches of concrete,
> masonry, pinhole microphones, thick wood walls, and so on.
>
> I can do the same thing with covert hardwired video cameras where I
> use a free running strobe light, and watch for the baseband sections
> of the spectrum to rise and fall in sync with the light burst, but
> not during the actual excitation and triggering of the bulb. I use a
> very tightly tuned antenna, but not only do I sniff for the
> horizontal sync signals, but also listen for the rising and falling
> video signal by using a comb filter to kill off the sync pulses
> starting about 2 lines up to about 15 lines so that I am hearing the
> amplitude variations of the video signal that is in line with the
> strobe, but not the sync signals themselves. I use a tightly tuned
> system to detect the fundamental and harmonics of the video sync, but
> a quais-broadband loop for the detection of the strobe pulses, but
> not the syc pulses.
>
> -jma
>
>
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Received on Sat Mar 02 2024 - 00:57:16 CST
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: Sat Mar 02 2024 - 01:11:44 CST