Homepage
Crypto
Spy radio
Burst encoders
Intercept
Covert
Index
Glossary
Cameras
Recorders
Radio
Bugs
Microphones
Concealments
Lock picking
Stories
Radio
PC
Telex
People
Agencies
Manufacturers
• • • Donate • • •
Kits
Shop
News
Events
Wanted
Contact
About
Links
   Click for homepage
SWM-44 B
Electret condenser microphone

SWM-44B is a subminiature covert electret microphone with a built-in pre-amplifier, developed around 1986, probably by Knowles, for the US Central Intelligence Agency (CIA). The device was intended for use with covert listening devices (bugs) and with covert communications systems.
 
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.
  
Gel microphone compared to the size of a hand

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.
 
  1. SWM is probably the abbreviation of Surveillance Wired Microphone.

SWM-44 B microphone cast in silicone SWM-44 B microphone Gel microphone compared to the size of a hand Sound port Sound port Close-up of the sound port Wiring
×
1 / 7
SWM-44 B microphone cast in silicone
2 / 7
SWM-44 B microphone
3 / 7
Gel microphone compared to the size of a hand
4 / 7
Sound port
5 / 7
Sound port
6 / 7
Close-up of the sound port
7 / 7
Wiring

Performance
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.

Measured performance characteristics. Click for a better view.


 
Further information

Any links shown in red are currently unavailable. If you like the information on this website, why not make a donation?
Crypto Museum. Created: Sunday 07 May 2017. Last changed: Tuesday, 13 June 2017 - 11:01 CET.
Click for homepage