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The image on the right shows the original Delta-V. It is a small handheld
device in a black plastic enclosure, with two antennas at the top. Also at
the top is the power switch (ON/OFF) and an attenuator for muting
strong local radio signals.
At the front is a small speaker that produces a ticking sound when searching
for bugs, much like a Geiger counter does when searching for radioactive
radiation.
The closer you get to the bug, the faster the ticking sound will be.
It is also possible, to use the device in silent mode, by connecting external
earphones at the top.
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The device measures the difference in signal strength between the two antennas.
When sweeping a room, any signal from a transmitter outside the room, e.g. a strong
local radio station, or a taxi passing by, is likely to be received equally strong
on both antennas. A rogue transmitter close to the device however,
such as a bug hidden in the room, will produce a different field strength on each
of the antennas, especially when the device is held within the nearfield
of the transmitter.
In 1991, DeltaV was succeeded by the improved
Delta-V ECM, which has a better dynamic range.
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The principle of operation is illustrated in the drawing below.
The strong broadcast transmitter
is relatively far away.
As a result, the signals that hit the antennas
will practically be equally strong (or weak).
The bug on the other hand,
is relatively close to the detector and is therefore likely to cause a
different field strength at each of the antennas and hence produce a stronger
reading.
The larger the difference,
the faster the clicking sound produced by the detector.
When held very close to the transmitter, the devices produces
a continuous tone. An attenuator switch on the top panel allows the Delta-V to
be used in close proximity of very strong radio signals.
It is also possible to use the Delta-V as a plain field strength indicator
by using just one antenna and leaving the socket of the other antenna empty
(or terminated). This makes the device more sensitive to weak radio signals,
but looses the advantage of cancelling out nearby radio stations.
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- Delta-V Differential RF Detector, Operating Manual
2-197-148. Audiotel International Ltd., Issue 3, January 1998.
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© Crypto Museum. Created: Friday 17 May 2013. Last changed: Monday, 07 October 2019 - 07:17 CET.
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