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Body transmitter with scrambler

TX-916 is a body-wearable covert transmitter, developed around 1994 by Audio Intelligence Devices (AID) in Fort Lauderdale (Florida, USA). It has an output power of 1 Watt and operates on a spot frequency in the 150-174 MHz VHF band, 1 using Frequency Modulation (FM). For added security, it has a built-in voice scrambler that can be enabled with a slide switch at the side.

The device measures 93 × 57 × 18 mm and weights 162 grams, batteries included. It has rounded corners and could easily be hidden under the clothing. In practice, the device was often worn in a special harness or taped to the body, along with microphone and antenna [A].

Different antennas and microphones were avail­able or request. Because the antenna is close to the body, the theoretical range of the transmitter is reduced, which is why the TX-916 has an out­put power of 1W. With fresh alkaline batteries, it can be used continuously for at least 3 hours. 2

Body transmitters are also known as a wire, and the person wearing it, is said to be wired. In covert operations, body transmitters were often preferred over body-wearable (tape) recorders, as they allow other officers to monitor and witness the operation, while maintining the possibility to record the conversation. For this reason, the TX-916 was commonly used in combination with the Unitel 225 portable listening post, which consists of a receiver with a built-in tape recorder.

The device is very similar to the TX-716, which has an output power of 250 mW. 3 it can be used with virtually any general coverage surveillance receiver, but was usually supplied in combination with a matching AID receiver, such as the analogue RX-905, the digital RX-1000 or the Unitel 225 intelligence kit. Due to its nature (VHF/FM) it can easily be detected by regualar TSCM equipment.

  1. 135-150 MHz by special request.
  2. More when Lithium batteries are used.
  3. The low-power TX-716 had a battery life of at least 24 hours.

TX-916 body transmitter with accessoriries
With antenna and microphone connected
Opening the battery compartment
With batteries installed (2 x 9V)
Bare transmitter
Noise cancelling electret microphone with short cable
Knowles electret microphone with long flexible cable
Knowles electret microphone
1 / 8
TX-916 body transmitter with accessoriries
2 / 8
With antenna and microphone connected
3 / 8
Opening the battery compartment
4 / 8
With batteries installed (2 x 9V)
5 / 8
Bare transmitter
6 / 8
Noise cancelling electret microphone with short cable
7 / 8
Knowles electret microphone with long flexible cable
8 / 8
Knowles electret microphone

The image below shows the TX-916 with its case shell removed. The actual transmitter measures only 40 × 57 × 18 mm and uses two common 9V battery cells that are connected in parallel. An antenna — usually a piece of wire — is connected to the mini BNC socket at the right. The socket at the left is for connection of an electret microphone. It accepts a screwable 2.5 mm mini-jack.

The device is enabled by setting the slide switch at the centre to the ON position. For protection against eavesdroppers, the build-in voice scrambler can be enabled by setting the slide switch at the side to the SC position. Although this provides basic protection against a casual (unintended) eavesdropper, it is no match for a professional interceptor as it only inverts the audio spectrum.

To prevent the batteries from falling out during an operation, the case shell was usually secured by means of tape. In the same vein, the power switch was often secured with a piece of tape as well, so that the transmitter could not be turned OFF accidentally by rubbing against it. This is why the ID label of the device shown here, is barely readable.

Compatible receivers
RX-905 analogue VHF/FM surveillance receiver
RX-905 digital VHF/FM surveillance receiver
Complete intelligence kit
  • Device
    Body-wearable transmitter
  • Purpose
    Evidence gathering
  • Model
  • Catalog
  • Manufactuter
    Audio Intelligence Devices (AID)
  • Users
    CIA, FBI, Police
  • Country
  • Year
    1994 (est.)
  • Band
  • Frequency
    150-174 MHz
  • Method
    Crystal 1
  • Channels
  • Modulation
    Narrow-band FM
  • Output
  • Antenna
    Wire (mini-BNC)
  • Power
  • Battery
    2 × 9V alkaline (type 1604)
  • Duration
    3 hours
  • Microphone
    Knowles electret with long wire
    Noice cancelling electret microphone (short wire)
  • Dimensions
    93 × 57 × 18 mm
  • Weight
    70 g (162 g with batteries)
  1. The device shown here operates at a spot frequency of 154.935 MHz.

  1. TX-716 / TX-916 - Operating Instructions
    Westinghouse, Audio Intelligence Devices, Inc.
    90035-18/G109107. Rev. 2, January 1996.
Further information
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Crypto Museum. Created: Friday 19 January 2024. Last changed: Monday, 22 January 2024 - 13:04 CET.
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