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
----------------------------------------------------------------------------------------------------
World Class, Professional, Ethical, and Competent Bug Sweeps, and
Wiretap Detection using Sophisticated Laboratory Grade Test Equipment.
----------------------------------------------------------------------------------------------------
James M. Atkinson Phone: (978) 546-3803
Granite Island Group Fax: (978) 546-9467
127 Eastern Avenue #291 Web:
http://www.tscm.com/
Gloucester, MA 01931-8008 E-mail: mailto:jm..._at_tscm.com
----------------------------------------------------------------------------------------------------
We perform bug sweeps like it's a full contact sport, we take no prisoners,
and we give no quarter. Our goal is to simply, and completely stop the spy.
----------------------------------------------------------------------------------------------------
Received on Sat Mar 02 2024 - 00:57:16 CST