FT817 Speech Compressor Install

As part of my efforts to improve the performance of my sota station, I have been focusing on the low hanging fruit of changes to help improve performance, better antenna, swapping the internal speaker, better filtering, the latest change is the audio out of the microphone!

I managed to find some time and confidence (i worry a little too much at my soldering ability some times) to have a crack at the FT817 Microphone speech compressor install. The little PCB arrived back in mid May from Hamshop.cz, but has sat on the desk waiting for me to find the screw driver and have a go at the microphone.

FT-817 Speech Compressor Ondřej Koloničný, OK1CDJ
FT-817 doesn't have any type of speech processing built-in.This audio speech compressor is designed with the Analog Devices SSM2165 device. The circuit is small enough that it can be built into the microphone.Gain of whole circuit is about 18dB, compression ratio is set by R1 and can be varied from 1:1 to 15:1. Output level can be set by R2, R3. Power consumption is around 7.5mA. Compressor is supplied directly from microphone, no external power supply is needed.


So tonight, i opened up the microphone and started on the process of modifying it and adding the speech compressor.

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The instructions are pretty simple, and the install is the same, simple, i just took my time ensuring i didn’t suff it up!. in all, from cracking open the microphone, to having it on air, (with my slow checking and soldering, it took me around 1hr, its not that complex, i just didn’t rush it)

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So, how does it work, on the local FM repeater, the B party knew it was on or off, their was a small increase in local noise at my end, like I have the microphone at my mouth, not 10cm away. on SSB, the bands were quiet, but I did test from a dummy load to my main radio on 144Mhz SSB to show the increase in “receive level” between off and on! watch the video below to see how much of a difference it makes 2-3’s points in my quick dirty test. if it increases the average “PEP” of the ft817 on a sota summit 2-3dB thats well worth the effort, it may make the difference for a city shack receiving station with lots of local noise. head over to Hamshop.cz if you are interested in this little nifty PCB.

6 thoughts on “FT817 Speech Compressor Install

  1. Hi Andrew

    Just wondering if you’ve been able to try it out on a summit yet. And if so, how did it go?

    BTW – Alex has run out of stock, trouble sourcing the chip

    Phil – VK2JDL

    • Phil. I have used it twice now. And haven’t been overly impressed. I had complaints of an RF feedback type of occurance. I need to put it on the bench and have more of a play. As the rf feedback/noise came and went. I may need to play with my wiring (I suspect it’s just that) when it worked without the noise. It seemed to increase signal levels. But the noise happened too often to really judge.

    • The ssm2165 ic is still available from “little diode” if u wish to build your own processor. I bought one last month and its running this circuit in homebrew configuration fine

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  3. Hi Andrew,
    I guess with the success of the other compressor you are not likely to have done any further work on this one. But I am wondering what antenna you were using when you did use this one in the field and what the odds are that your radio and microphone were hot with RF. eg was the antenna close, an end fed antenna, or an asymmetric feed. I use the compressor in the IC703 and I think it helps with marginal signals so I’m equally interested in improving the talk power of the FT817 as I use it for SOTA VHF work and for microwave bands (when I remember to take the entire microwave setup, dish etc).
    Andrew VK1DA

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