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I have been using the FT-857 on FT-8 and JT-65 from home and DX expeditions mainly on 50 MHz. Usually I run full power. I have not seen thermal issues, but mostly I am on top of mountains.

There seems to be one fundamental issue with the 857 in its SSB modulation circuit. We have analyzed multiple?857 and looked in deep into the circuit and probed every stage on the modulation path.?

The 857 has rather strong distortions in its SSB modulation path. For example, if you drive it with 600Hz, you will see, rather strong 1200 and 1800 Hz. This is not a function of the power level. This is caused in the modulation circuit. The reason is the modulator IC selected. It is driven beyond specification on the audio port, thus, it distorts. Other rigs, like my Kenwood 480 are much better in this regard.

This problem normally unnoticed, some people think that the SSB audio sounds somewhat not really clean. But in FT-8 this grows to a serious issue. For example, if you transmit at 50.3135 MHz (so 500 Hz audio) you will also transmit at 50.314, the second harmonic of the audio. The harmonic signal is like 40 or 60dB down, but if somebody else uses that frequency you will block it if the stations are close to each other, or if you are on an excellent location on a mountain. People will start to complain about your signal having spurious. In FT-8 this matters, as teh actual used bandwidth is just 60 Hz.?

After analysing this issue on multiple 857 and understanding the circuit from probing I stopped using the 857 for FT-8.

73? ?

? ? David? ?OE6NZM / AD0PY / DL7ZM? now in Graz, Austria