Locked Re: FST4 modes with TS-890S - slow RF envelope rise problem #txaudio


Well said, Peter.

Karl, I was not suggesting it be changed for one person. There are already several affected by this and the FST4(W) mode is new, not even out in a GA release yet. There will be more who run into issues with this. Neither is it just one amplifier design that is or will be affected, but many.

I find it ironic that waveform shaping seems to have appeared for the first time in WSJT-X (I am not aware of older modes that use it) in modes designed for LF and MF where the majority of amplifiers cannot reproduce the shaping and may have other problems as a result of it. This kind of waveform shaping might make sense on bands where most people use linear amplifiers. That's just not the case on the bands this mode was targeted at.


On 1/6/2021 10:52 PM, Peter Hall, VK6HP wrote:
If you'll permit me to comment, it's not a matter of revising the software to work with one design.  LF/MF users, where the FST4 modes are targeted, very often use highly efficient, non-linear amplifiers (such as Class D or E) with the prevailing digital and CW modes.  Within these common designs the proper place to control RF envelope shaping is in the amplifier, not the exciter and, indeed, the usual topologies cannot reflect any exciter waveform shaping in their outputs.  Furthermore, not only is exciter waveform shaping wasted, it's counterproductive in a spectral containment sense if it leads to some amplifiers emitting spurious transients.
While I strongly suspect the present heavy envelope shaping can be reduced to keep everyone happy (as they are with WSPR, JT9, ...), another simple solution is to have the option to allow LF/MF users to retain or disable shaping, catering to both linear PA users and the large body of non-linear amplifier users.  In the end, there's no point making life difficult for a large fraction of the target user base, especially if the ambition is to have the FST4 modes replace the earlier modes.
73, Peter.

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