Welcome to the Military Radio Accessories Specification Page

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You will find listed on this page various information related to military radios. This includes specifications for audio accessories like handsets and microphones plus, pin-out and plug information for most popular sets.

Feel free to browse or select a specific product from the shortcut list.

HANDSET: H-138(*)/U
The H-138 handset is equipped with a noise-cancelling dynamic microphone element. The handset's microphone section incorporates 2 elements, each under a separate opening. When a user speaks into one opening, the other electrically cancels or reduces outside noise thus preventing its transmission along with the user's voice. The H-138 specifications are similar to that of the H-189/GR and H-250/U handsets.

HANDSET: H-189/GR
The H-189/GR handset is more rugged than the H-138(*)/U handset and does not have a noise-cancelling microphone. Specifications are similar to that of the H-250/U handset.

HANDSET: H-250/U
The H-250/U handset is now the standard handset used for tactical field communications requirements. It is utilized with manpack and fixed station radio and telephone equipment. The H-250/U features a press-to-talk switch, a retractile cord and is terminated with a 5 pin U-229U audio connector. The microphone element is of the noise-cancelling type.

HANDSET: H-350/U
The H-350/U handset is now the standard handset used for tactical field telephone sets. It is utilized with both analogue and digital voice terminals such as the TA-954/TT Digital Non-Secure Voice Terminal. Unlike its twin brother, (the H-250/U), the H-350/U is not compatible with radio equipment sporting 6 pin audio connectors. The principle design of this handset is to provide 'hot mic' capabilities thus allowing for full-duplex operation over telephone circuits. This is accomplished by changing the method by which the microphone is wired to the PTT switch and by the addition of an extra ground lead to the microphone capsule and pin F of the audio connector. The H-350/U features a press-to-net radio interface switch for activating remote radio transceivers, a retractile cord and is terminated with a 6 pin audio connector. The dynamic microphone element is of the noise-cancelling type the frequency response has been enhanced for intended use with encryption units.

HANDSET: H-4800
This is the current issue British Racal/Clansman H-4800 handset. As more details become available, they will be listed here.

Schematic Diagram (H-4800)

HEADSET: H-251(*)/U
The H-251(*)/U headset is of the single headband construction and is equipped with 2 dynamic earphones. The headset's specifications feature an impedance of 1000 Ohms and a frequency response of 20 to 3,500 Hz. The 36 inches long audio cord is fitted with a clothing clip and is terminated with a U-229/U connector. Variants in the nomenclature includes the H-251A/U and the LS-549( )/PRC.

MICROPHONE: M-80C/U
The M-80C/U microphone is the standard microphone used for tactical field communications equipment. It is utilized with manpack and fixed station radio and telephone equipment. The M-80C/U features a press-to-talk switch, a retractile cord and is terminated with a 5 pin U-229U audio connector. The microphone is of the noise-cancelling type.

LS-166/U
The LS-166/U is the loudspeakers employed with the older style military radio sets which employed a U-79/U audio connector. Features include a mounting bracket as part of it's rectangular enclosure, a 4 inches, 3 Watts, 8 Ohms permanent magnet cone type speaker and is coupled through a sealed, 8 Ohms to 600 Ohms impedance transformer. A side mounted switch allows for the selection of "Field or Pack Set Use" or "Vehicular Set Use" modes. This switch selects audio input from 2 different pins on the audio connector (refer to schematic diagram). The connecting cord is terminated with a U-77/U connector.

LS-454/U
The LS-454/U is one of the most popular loudspeakers employed with military radio sets. The speaker can practically be employed with any radio and is of a water proof design. Features include a mounting bracket as part of it's rectangular enclosure, a 4 inches, 2 Watts, 8 Ohms permanent magnet cone type speaker type LS-445/U and is coupled through a sealed, 8 Ohms to 600 Ohms impedance transformer. The connecting cord has been seen with various terminations such as a U-229/U connector or a PJ-055B (1/4") jack.

AM-4979/GR
The AM-4979/GR is an amplified version of the popular LS-454/U loudspeakers. The speaker was designed for use with speech security equipment (SSE) / cryptographic equipment such as the TSEC/KY-38 (circa 1964) and TSEC/KY-57 (circa 1975) but can be easily employed with any radio. The design is water proof and features a mounting bracket as part of the enclosure. A 4 inches, 2 Watts, 8 Ohms permanent magnet cone type speaker, type LS-445/U is employed and input to the amplifier stage is of high impedance. The enclosure also includes a built in U-183/U audio connector for the addition of a microphone or handset. Internally, the AM-4979/GR incorporates an audio amplifier and support circuitry. The connecting audio cord is terminated with a U-229/U connector and is permanently affixed to the enclosure with a strain relief. DC power is supplied via an MS-3114E8-4S connector which is coupled with cable assembly CX-12925/U MODIFIED. The amplifier will not provide sidetone to the speaker during the transmit cycle and is muted by an internal relay. With a simple circuit modification, it is possible to provide sidetone during transmit.

Schematic Diagram (AM-4979/GR)

AM-6747/V
The AM-6747/V is an fully upgraded and improved version of the amplified loudspeaker AM-4979/GR. The speaker was designed for use with speech security equipment (SSE) / cryptographic equipment such as the TSEC/KY-38 (circa 1964) and TSEC/KY-57 (circa 1975) and can be easily employed with any radio. The design is water proof and features a mounting bracket as part of the enclosure. A 4 inches, 2 Watts, 8 Ohms permanent magnet cone type speaker, type LS-445/U is employed and input to the amplifier stage is of high impedance. The enclosure also includes a built in U-183/U audio connector for the addition of a microphone or handset. Complete isolation of the keying circuit (PTT) is provided by a relay. Internally, the AM-6747/V incorporates an audio amplifier and support circuitry. The audio input connection is achieved by the use of a enclosure mounted MS-3114E10-98S connector. A user provided cord with the proper terminations is required. DC power is supplied via an MS-3114E8-4S connector which is coupled with an appropriate cable assembly. The CX-12925/U cable can be employed to power the unit. The amplifier will not provide sidetone to the speaker during the transmit cycle and is muted by the internal relay. With a simple circuit modification, it is possible to provide sidetone during transmit.

Schematic Diagram (AM-6747/V)

U-182B/U, U-229/U
These connectors are the standard military audio connectors as found on handsets, microphones, headsets and speakers. The most common is the U-229/U. It accommodates the standard military coiled or straight audio cables. The U-182B/U is electrically identical. The only differences are in the shell body material and in its cable strain relief. Its distinguishable features are its shell colour (black) and the fact that it employs a small cable opening which is accompanied with a black rubber gasket instead of the traditional spring strain relief.

U-183/U
The U-183/U connector in the standard 5 pin audio connector as found mounted on the chassis of most military radio equipment. It is the chassis mounted mate for the U-229/U and U-182B/U audio connectors. The pin out information is identical to the U-229/U type connectors mentioned above.

GC 283
The GC 283 connector is the 6 pin version of the U-183/U. It is now common on modern radio and cipher equipment and accessories. Pin "F" normally carries DC voltage to power accessories and commsec equipment. In some instances, it may also carry data when the connector is used, for example, to interface between a terminal device and a printer.

GC 329
The GC 329 connector is the 6 pin version of the U-229/U. It is most commonly used with modern radios, cipher equipment and key fill devices. Pin "F" normally carries DC voltage to power the accessory or commsec equipment. In some instances, it may also carry data when the connector is used, for example, to interface between a terminal device and a printer, between 2 radios for cloning purposes or, to carry key fill programming data. The GC 329 is the mate to chassis mounted GC 283.

U-77/U and U-79/U
The U-77/U and U-79/U connectors are generally found on older radio sets. They are a 10 pin/contact connector. The U-77/U is the cable (handset) plug and is matted to the chassis mounted U-79/U jack. There are many variations in the wiring of this connector. Below is the common pin-out and related information that apply to standard military radio use.

PRC-25/77, PRC-70, RT-524
X-Mode connectors on receiver/transmitters are generally use for the routing of transmit and receive audio to ancillary equipment such as cryptographic equipment. In its most simple form, it is also used to provide external DC power to the RT such as in the case of a vehicular mounted PRC-25 or PRC-77.

The information that follows will provide you with the "shorting jumper" pin-outs found in various X-MODE connector plugs.

PRC-25/77: Pins E to F, L to H and L to M.
PRC-70: Pins E to F and L to R.
RT-524: Pins A to C, D to I and E to G.

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Revised: June 08, 2017
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