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Delta V   Delta-V ECM
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.

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.
  
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 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.

Delta-V ECM
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.

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.
  
Delta-V in operation (shown here without antennas)

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.

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 Delta-V in operation (shown here without antennas) Delta-V ECM bottom panel

Technical specifications   Delta-V ECM
  • 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
References
  1. Audiotel International Ltd., Delta V ECM - Operating Manual
    2-197-244. 1998. First released October 1996.
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