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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