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Delta-V ECM
Differential RF Detector

Delta-V ECM is a handheld differential detector for covert listening devices (bugs), introduced in 1991 by Audiotel in Corby (UK) as the successor to the original Delta-V. It allows quick scanning of rooms, people, vehicles and other objects, by brushing over them. Although the device was often used alongside existing Scanlock receivers, it can also be used as a stand-alone device.

Delta-V ECM is an improved version of Delta-V, and is housed in a slightly larger enclosure. the two antennas have been placed further apart and have more robust SMA sockets. Furthermore, the device has an improved dynamic range and a better frequency response, uniform to 6.5 GHz.

In use, Delta-V ECM produces a ticking sound, much like a Geiger counter does when sensing radioactivity. When getting closer to the bug, the ticking becomes faster. Right on top of the bug, the tone will be continuous. The volume of the tone can be adjusted with a knob at the bottom.
  
Operating the Delta-V ECM

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.

Delta-V and it successors have been on the market for well over 30 years, providing an easy to use and cost-effective means to search objects for bugs. Despite its simple appearance, it is a powerful and very effective tool that should be part of the basic configuration of every sweep team. Delta-V ECM was succeeded in the mid-2000s by the similar looking Delta-V Advanced, which has the added capability of detecting burst transmissions in the 50 MHz to 15 GHz range.

Operating the Delta-V ECM Handheld Delta-V ECM Delta-V ECM Delta-V ECM with both antennas installed Two antennas installed Delta-V ECM with open battery compartment
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Operating the Delta-V ECM
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Handheld Delta-V ECM
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Delta-V ECM
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Delta-V ECM with both antennas installed
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Two antennas installed
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Delta-V ECM with open battery compartment

Controls
The diagram below provides a quick overview of the controls and connections on the body of the Delta-V ECM. The device is constructed in such a way that it can easily be carried in one hand. At the top are two SMA antenna sockets on which the supplied rigid antennas should be installed.


At the bottom is a volume knob, which also acts as the ON/OFF switch. When turned fully anti-clockwise, the device is OFF. Power is provided by a standard 9V block battery that should be installed behind the removable panel at the front. Approx. 10 seconds after switching ON, the device is ready fo use, and a clicking sound will indicate the presence of any
RF
signals. The sound is produced by the built-in speaker or, when connected, through the (optional) earpiece.

When (too) close to an RF source, the sensitivity can be reduced by pressing the push-button at the side. It is also possible to use the detector as a regular field strength indicator by using just one antenna and leaving the other SMA socket empty (or terminated). This makes the device more sensitive to weak radio signals, but looses the advantage of cancelling out nearby radio stations.

Bottom side Two antennas installed Bottom panel with ON/OFF/Volume knob and 3 mm socket for earphones Speaker and power indicator Pressing the push-button Battery cover retaining bolt Bottom side Delta-V ECM with open battery compartment
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Bottom side
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Two antennas installed
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Bottom panel with ON/OFF/Volume knob and 3 mm socket for earphones
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Speaker and power indicator
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Pressing the push-button
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Battery cover retaining bolt
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Bottom side
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Delta-V ECM with open battery compartment

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 push-button, on the right side panel, allows the device to be used in close proximity of very strong radio signals.



Disassembled Delta-V ECM

Interior
Delta-V ECM is housed in an extruded aluminium enclosure that is sprayed in a fine grey texture, similar to other members of the ECM range. It measures 122 x 62 x 22 mm and weights just 238 grams, incuding the battery and the antennas, making it the ideal companion for a site survey.

The interior can be accessed by releasing the large battery cover bolt at the rear of the device, and one large phillips screw – also at the rear – after which both the battery cover and the front panel can be removed. In order to remove the
PCB
from the enclosure, the remaining four screws at the rear panel should also be removed.

The image on the right shows the part of the
PCB
that contains the tone generator and the audio amplifier. It becomes visible when the battery lid is removed and produces the clicking sound that indicates the presence of a nearby radio signal.
  
Electronic circuit

The double-sided PCB has components on both sides, although most parts are located at the top, which is the side that is visible when the device is first opened. The bottom side is fitted with Surface Mount Devices (SMDs) only. The PCB has a large cut-out to accomodate the 9V battery.

Bottom side Delta-V ECM with open battery compartment Disassembled Delta-V ECM Electronic circuit Inside the Delta-V ECM PCB PCB - top side PCB - bottom side
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Bottom side
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Delta-V ECM with open battery compartment
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Disassembled Delta-V ECM
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Electronic circuit
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Inside the Delta-V ECM
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PCB
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PCB - top side
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PCB - bottom side

Block diagram
Below is the block diagram of the device. At the left are the antenna inputs (ANT 1 & ANT 2), followed by two (matched) schottky barrier diode detectors, of which the outputs are fed to a low-noise wide-dynamic-range differential logarithmic DC amplifier with offset cancelling and automatic drift compensation. The signal is amplified in a second logarithmic amplifier and then rectified, to produce a DC voltage proportional to the strength of the differential input signal.


The proportional DC level from the rectifier drives a Geiger-type click generator that produces a rising tone when getting closer to the transmitter. The audio signal from the click generator is amplified and then delivered to the internal speaker (or alternatively to the external earphones).


Technical specifications
  • Frequency
    ± 5dB, 10 MHz to >6.5 GHz
  • Sensitivity
    -53 dBm
  • Dynamic range
    >50dB, typically -52dBm to +5dBm at 1GHz
  • Power source
    9V alkaline PP3 (24 hours of continuous operation)
  • Size
    122 x 62 x 22 mm
  • Weight
    238 g (including battery and antennas)
Documentation
  1. Delta-V ECM, Instruction Handbook
    201-042. Audiotel International Ltd., Issue 1, November 1991.

  2. Delta-V ECM, Instruction Handbook
    201-042. Audiotel International Ltd., Issue 3, january 1998.
Further information
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Crypto Museum. Created: Sunday 06 October 2019. Last changed: Monday, 07 October 2019 - 07:59 CET.
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