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The image on the right shows a typical 1 SWM-44B. The microphone element
measures approx. 7 x 4 x 3 mm and is cast in a flexible silicone-like
stick that has a diameter of 9.5 mm and is 39 mm long. It has a fixed
1 metre long black shielded cable that exits the stick at the rear.
At the front is a cone-shaped cavity that guides the sound to the
microphone's sound port which consists of short a 1 mm tube with a
perforated grid.
Inside the stick, part of the insulation of the
cable has been removed before it was cast in silicone,
to provide some level of strain relief.
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The cable is 2.5 mm thick and contains three wires (red, black and
white) plus a shield. The wires are stripped at the other end, but a plug is
not provided. Depending on the application, a suitable plug would be mounted
later. This would be the case, for example, when the microphone is used
with a covert radio.
When used in combination with a
covert listening device (bug),
the wires were often soldered directly to the transmitter.
The silicone body reduces low-frequency vibrations.
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SWM is probably the abbreviation of Surveillance Wired Microphone.
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Each SWM-44B microphone was supplied with an idividual test report that shows
the frequency response of the device. Below is an example of such a
test report, as supplied with an SWM-44B on 17 January 1986.
The performance was measured with Brüel & Kjær test equipment.
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© Crypto Museum. Created: Sunday 07 May 2017. Last changed: Tuesday, 13 June 2017 - 11:01 CET.
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