[Elecraft] K3S Shift Setting for WSJTX

[Jim Brown]

Richard,

Not nonsense at all.  WSJT-X is VERY robust in the ability to reject 
this sort of QRM. The screen grab below is a great example.  I continue 
to be amazed by the decoding in WSJT-X. About 10 days ago, W0OGH 
accidentally got out of sync with JA7QVI, calling on his TX cycle, and 
on the same frequency. As this screen grab clearly shows, W0OGH was 9 dB 
stronger on the 0053Z cycle and 12 dB stronger on the 0055Z cycle, yet 
both signals were decoded without error!

During a wonderful 6M opening this past Friday evening west coast time, 
I had a LOT of JT65/JT9 passes with more than 20 clean decodes on each 
pass. I regularly see decodes in the -20 to -28 range, even with very 
strong signals capturing the AGC. It's only necessary to keep peak 
signal levels to the A/D below digital clip.

73, Jim K9YC

=   =   =   =   =   =   =   =  =   =

0053 -23  0.3 2788 @  K1JT W7AH DM42

0053 -14  0.1  817 #  JA7QVI W0OGH DM52

0053 -24  0.0 1274 #  CQ DX JF3DRI PM74

0053 -14  0.2 1590 #  N4GBK N6ML CM97

0053 -23  0.6  817 #  CQ DX JA7QVI QM08

------------------------------------- 6m

0055  -7  0.1  817 #  JA7QVI W0OGH DM52

0055 -22 -0.0 1274 #  CQ DX JF3DRI PM74

0055 -16  0.2 1588 #  N4GBK N6ML R-07

0055 -19  0.6  816 #  N6WS JA7QVI R-06


On 7/4/2017 1:47 PM, Richard Lamont wrote:
> On 04/07/17 18:37, Jim Brown wrote:
>
>> The split mode in WSJT-X is simply a crutch for those who don't know (or
>> don't care) how to set audio levels so that distortion is not produced
>> in the audio chain.
> Sorry, but that's nonsense.
>
> With a strong signal, just 1% distortion will produce audio harmonics
> that are only 40-ish dB down on the fundamental. That's plenty to cause
> QRM. With these modes it's possible to have work a station that's 60 dB
> down on another just a few Hz away. WSJT-X, being based on 16-bit
> digital audio, has an inherently high dynamic range.
>
> The split mode exists (a) to enable people to work over a wider range of
> frequencies than a single SSB channel, and (b) to ensure that the Tx
> audio frequency is always at least 1500 Hz, ensuring that *low-level*
> harmonics get filtered out. Even with a clean TX and audio levels set
> just so, it's well worth having that extra filtering in place.
>
> 73,
> Richard G4DYA
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