H-350/U Handset

Brooke Clarke, N6GCE

H-350 Handset

General Infromation

This handset is made for use with U.S. Army digital telephones.  It uses the U-183 6 pin connector rather than the more common U-229 5 pin connector.
The sixth pin (F) is used to provide a connection to the microphone that is hot while the earpiece is also hot thus allowing normal duplex operation of the microphone and earpiece at the same time.
Photo of H-350/U showing the 6 pin connector
Circuit diagram of H-350/U courtesy of Richard Lacroix of MILSPEC Communication

When the Push To Talk switch is pressed it does two things:

  • Connect pin C to ground (pin A) for the Push To Talk function just like on the H-250 handset
  • Grounds (pin A) the microphone while the hot microphone line (pin D) is still connected, pin F also is grounded.

  • Note that with PTT released that the microphone has no connection to pin D so the H-350 does work on radios that have the U-228 5 pin audio connector like the PRC-68
    Grounding pin C (PTT) while pin F has a path to ground (through the microphone) on a PRC-126 ( and most likely on all the squad radios with a 6 pin U-182 connector) will cause the radio to output TTL data on pin F. The data can be heard as digital noise coming  from the microphone, not the earpiece.  This use of the H-350 is for experimentation rather than a functional use.

    The H-350 will NOT work on radios like the PRC-126 that have the 6 pin U-183 connector.

    Maintenance Instructions

    This is a U-229 Audio connection.

    Ohm Meter Readings:


    NSN 5965-01-128-3944 made by Sonetronics

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