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Delta V
Differential RF Detector

Delta V was a handheld differential detection device for covert listening devices (bugs), developed in the late 1980s by Audiotel in Corby (UK). It allows quick scanning of rooms, people, vehicles and other objects. Although the device was commonly used alongside existing Scanlock receivers, it can also be used as a stand-alone device. Delta-V was succeeded in 1991 by the Delta-V ECM.

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.
  
The original Delta-V bug detector

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.

The original Delta-V bug detector
Delta-V differential RF detector
Delta-V seen from the top
Close-up of the top panel
Delta-V interior
Close-up of the interior
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The original Delta-V bug detector
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Delta-V differential RF detector
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Delta-V seen from the top
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Close-up of the top panel
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Delta-V interior
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Close-up of the interior

Principle
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.


Documentation
  1. Delta-V Differential RF Detector, Operating Manual
    2-197-148. Audiotel International Ltd., Issue 3, January 1998.
Further information
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Crypto Museum. Created: Friday 17 May 2013. Last changed: Monday, 07 October 2019 - 08:17 CET.
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