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H-250/U military handset with BitX40?

Gil F4WBY
 

Hello,

I want to use an H-250/U, specs:

EARPHONE: 1000 OHMS

MICROPHONE: 150 OHMS

A loud whistle outputs 2.5 mVAC.

I know there is an impedance issue here but also an output voltage issue... Any suggestions on how to solve the problem?

Thanks!

Gil.
Leonardelli
 

I love the use case Gil. I would think the clansman would be better. I gave up trying to use mine as i had a lot of difficulty find a matching connector.


Did you take the connector off?


John ve3ips
 

Hi Gil:

I believe that's a dynamic mic and the BITX-40 module is designed for an electret (condenser). ?But the conversion should be possible if you add a blocking capacitor to take off the DC bias (needed to power the electret capsule) and add some gain. ?Keep in mind that the electret mic has a FET pre-amp inside of it.

All of that said, I've been trying to get a M-80/U microphone working for some time without success. ?The M-80/U has identical specs (I'm sure there is a millitary standard being followed here). ?The issues I'm having are related to RFI and not to the audio. ?For some reason that I've not been able to work out yet, when I go into transmit mode the output power goes to max and I can see RF in the audio stages using a scope. ?

Some day I'll get this sorted out and will let you know.?

73s,

Bruce KC1FSZ
 

An Electret microphone like that used with a BITX-40 puts out around 45 mv of audio.? Any replacement
microphone should provide similar signal level.

Some microphones need to be bypassed for RF.? If RF is present on the microphone input it can be
rectified and taken as audio input, causing system oscillation and indications of full RF? power output.

Arv? K7HKL
_._


On Wed, Apr 26, 2017 at 8:38 PM, <bruce@...> wrote:

Hi Gil:

I believe that's a dynamic mic and the BITX-40 module is designed for an electret (condenser).? But the conversion should be possible if you add a blocking capacitor to take off the DC bias (needed to power the electret capsule) and add some gain.? Keep in mind that the electret mic has a FET pre-amp inside of it.

All of that said, I've been trying to get a M-80/U microphone working for some time without success.? The M-80/U has identical specs (I'm sure there is a millitary standard being followed here).? The issues I'm having are related to RFI and not to the audio.? For some reason that I've not been able to work out yet, when I go into transmit mode the output power goes to max and I can see RF in the audio stages using a scope. ?

Some day I'll get this sorted out and will let you know.?

73s,

Bruce KC1FSZ

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