On 7/23/2024 11:41 AM, Black Michael W9MDB via wsjt-devel wrote:
Was looking at this example SuperFox transmission using Audacity
https://www.dropbox.com/scl/fi/stohwy3veidevmwr4j517/240605_181330.wav?rlkey=85h1c9riskq1mmbqzex9hpov3&dl=1
<https://www.dropbox.com/scl/fi/stohwy3veidevmwr4j517/240605_181330.wav?rlkey=85h1c9riskq1mmbqzex9hpov3&dl=1>
It looks like there is amplitude modulation going on which would seem to
be undesirable.
As stated in the second sentence of the SuperFox User Guide, SuperFox
always transmits a full power constant envelope waveform:
https://wsjt.sourceforge.io/SuperFox_User_Guide.pdf
Except for a 10 msec ramp-up at the start of transmission and ramp-down
at the end, the audio waveform sent to the transmitter is 100% constant
envelope.
The signal you examined in file 240605_181330.wav passed through a Tx
filter, propagated over a trans-continental channel with selective
fading, and then through a Rx filter. Frequency-dependent amplitude
changes can occur in any of those stages, and there's nothing
'undesirable' about their existence.
-- 73, Joe, K1JT
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