Thursday, 22 January 2015

Planning a new mic interface for FT-857D

My Yaesu FT-857D is equiped with a homebrew interface box that allows me to use either the stock fist mic, or a modified ex-telco Plantronics headset, along with a remote manual PTT button. This is a good system, but has three drawbacks -

1. The mic level out of the headset (which gives by far the best audio) is much greater than that from the stock mic, and hence the radios mic gain setting for ideal SSB modulation with the headset means the fist mic is almost unhearable!

2. I have no way to inject DTMF tones into the mic line to use IRLP and Echolink, and I dont have a DTMF mic!

3. The current arrangement is also not open to use with my proposed Bluetooth mic system.

So, I have redesigned the interface. The new version will include a 1:1 audio transformer in the mic line, and a level control pot, to allow injection of DTMF tones from an external dialler, or, audio from the Bluetooth receiver. There will also be a level control pot in the mic line from the Plantronics headset, to allow the level to be turned down to match the fist mic, and so let the radios mic gain be set to the best for both. A switch will be provided to select between the two main mic inputs.

Ive seen cheap copy Chinese DTMF mics on ebay, these look like the Yaesu mics, but I dont know if they are exact copies, or whether I could make one work properly with the FT-857D. If they can, then one of these would eliminate the need for an external dialler.

I dont know when i'll be able to put this together, it all depends on finding a small but suitable box for the interface.

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