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Differential RF Detector
Delta V and the later Delta-V ECM are small pocket-size bug tracers,
developed by Audiotel in Corby (UK) in the late 1980s.
The small hand-held device, allows quick scanning of a room, a person
or a car, for eavesdropping transmitters (radio bugs).
Although it was often used by sweep teams alongside existing
Scanlock receivers,
it can perfectly well be used on its own.
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The image on the right shows the original Delta-V. It is a small hand-held
device in a black plastic enclosure, with two antennas at the top. Also at
the top is a power switch (ON/OFF) and an attenuator for 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 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.
The effect is illustrated in the drawing above. The strong broadcast transmitter
(blue) is relatively far away. As a result, the signals that hit antennas A1 and A2
will be nearly equally strong. The bug on the other hand (red), is relatively close
to the detector and will therefore produce a different field strength in nearly
every part of the room. As Delta-V measures the difference in field strength between
the two antennas, the bug will therefore produce a stronger reading.
The stronger the difference in signal, the faster the ticking sound produced
by the detector. When you are right on top of the transmitter, Delta-V will produce
a continuous tone. A switch on the top panel allows the Delta-V to be used in
close proximity of very strong radio signals.
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In the mid-1990s, Delta-V was succeeded by the Delta-V ECM, that can be seen
as an improved version of the earlier Delta V. The device is slightly bigger
and is housed in an grey aluminium enclosure. The antennas are placed further apart
and have more robust SMA sockets.
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Furthermore, the audio level of the Geiger ticker is now adjustable with a potentiometer
at the bottom that also acts as the ON/OFF switch. An LED on the front panel shows
when the device is switched ON. Headphones can be connected to the 3mm jack socket at
the bottom. When no headphones are connected, the small internal speaker is used.
A typical Delta-V ECM (in ECM colours) is shown in the image on the right.
The device can be opened by loosing the large bolt at the rear side with a screwdriver
or a coin. This gives access to the battery compartment.
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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 main advantage of ruling out local radio stations.
Delta-V and the Delta-V ECM have been on the market for many years,
providing a simple, lightweight and cost-effective means for tracing bugs
quickly in a room or in a car. Despite its simple appearance, it is
a very powerful and effective tool that should belong to the basic setup of
every sweep team. Audiotel
currently sells the Delta-V Advanced
that succeeded the Delta-V ECM in the mid-2000s. It contains a LED-bar field
strength indicator and has the ability to detect burst transmissions,
anywhere in the frequency spectrum between 50 MHz and 15 GHz.
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Technical specifications
Delta-V ECM
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- Frequency response: ± 5dB, 10 MHz to >6.5GHz
- Sensitivity: -50dBm average
- Dynamic range: >50dB, typically -50dBm to +5dBm at 1GHz
- Power source: 9V alkaline PP3 (24 hours of continuous operation)
- Size: 122 x 62 x 22 mm
- Weight: 245 g
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- Audiotel International Ltd., Delta V ECM - Operating Manual
2-197-244. 1998. First released October 1996.
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© Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Sunday, 19 May 2013 - 14:06 CET
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