H-250/U Handset

©Brooke Clarke, N6GCE


	Noise Canceling mikes on back and end

General Information

This dynamic noise canceling mike type handset is the standard for many PRC-nnn series radios.

IMPORTANT - Many people don't realize how good the noise canceling feature is. They hold the mike 1/2 to 1 1/2" from their mouth, then complain that the handset has low output or that the radio has weak modulation. That's because of the noise canceling.

YOU MUST HAVE THE MIKE TOUCHING YOUR LIP!

This handset was designed for use under combat conditions which includes explosions, heavy trucks or tanks driving nearby, etc.

Photo -
Label on Handset:

Handset H-250/U
Sonetronics
Contract
DAAB07-87-C-T017
U.S.

Intended Use

Handset H-250()/U utilitizes a 1000 Ohm earphone element, a 150 ohm dynamic noise canceling microphone, a push-to-talk switch and a six foot (extended) retractile cord terminating in a 5 pin audio connector (U-182/U). It is intended for uee with military man-pack radio equipment such as the AN/PRC-70 and AN/PRC-77. Handset H-250()/U can be uesd in place of Handset H-189/GR. The H-250( )/U handset assembly is a disposable item.<>
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NSN

5965-00-043-3463

5965-01-247-4723

Maintenance Instructions

Ohmeter Readings

A (gnd) to B (ear) = 1,000 Ohms

A (gnd) to C (PTT) = normally open, 6 Ohms PTT pressed

A (gnd) to D (mike) = normally open, 150 Ohms PTT pressed

A (gnd) to E (External) = always open

Speaker
Using an HP 204 Audio Oscillator and the TS-585 Audio Level Meter the AC impedance of the H-250 can be seen to be about 1,500 Ohms.
It is common for the AC impedance to be higher than the DC resistance because of the inductance of the coil. Some of the early headphones used with crystal radios had an AC impedance up to 10,000 Ohms but had much lower DC resistance.

A 0 dBm tone at 1 kHz into the earpiece is loud when the ear piece is held to the ear and can still be heard with the H-250 on the bench.
A 4 kHz tone is loud with the H-250 on the bench.

Mike

Agilent 4395A spectrum analyzer 1 Hz to 5 kHz, PTT pressed, whistle into microphone. On the most sensitive range (-10 dB) of the TS-585C/U there is no meter movement with a loud whistle. A Fluke 87 DMM set to ACV will show about 1.2 mV with PTT pressed in a quiet environment. With a loud whistle the reading might get to 2.5 mVAC.

This mike will not drive a PC audio line level input. It needs amplification first.

Push To Talk Switch

I have heard that there's a magnet inside the switch proper.
Photo shows the switch seperated from the handset.

H-356 Handset

The Regency net radios use the H-356 which is slightly different than the H-250. In the stock H-250 the mike, speaker and PTT share a common ground on pin A.

In the H-356 the Mike ground is seperated from pin A and connected to pin E.

Links

Sonetronics - H-250 Handset

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