Desk Microphone

PZT PTT Box - with labelling

Several years ago I built a desktop console box to mount a desk microphone onto…  I used “in-stock” items from the component box: PTT switch, tone-burst/tune button plus level/tone controls – The desk mic was just 30cm of RG213 with a PL-259 at one end and an electret capsule at the other.  The picture here shows how I added some labelling to make it look quite nice.

This seemed to work quite well as a simple PTT/Mic-mount so I improved the internals to include a speech processor based on the SSM2166 audio chip.  The important feature of this chip is the noise-gate, allowing residual noise and background-QRM to be attenuated during gaps in speech.

After I purchased the FT-857D, I wanted something for that so I could natter on 2m FM/SSB without using the fist-mic – so I came up with the following…

The circuit shown below can easily be fitted into a small plastic project box (the only thing I had to buy for this) – I opted to use a phono plug+socket combo for the boom-mic.  The boom is just some thin screened audio cable and a few lengths of thick tinned wire.

The whole ensemble is then covered in heat-shrink tubing.  The parts are readily available from CPC or Maplin – the switchable lo-cut filter is optional but can be helpful if your radio doesn’t have any EQ settings.  The output trimmer is also option as this will depend upon your radio and the output of the electret capsule.

To give you some idea of output levels – My FT-950 (at the time) required a Mic Gain setting of 27 for the stock (dynamic) MH-41 fist-mic but only 16 for this Desk Mic.

A nice simple project to keep you out of trouble for a few hours…