Igor --
On 1/22/2016 12:48 PM, Игорь Ч wrote:
> In the latest WSJT-X release we still have large unwanted side
> spectrum emissions at beginning and end of the message transmission.
I consider it a gross exaggeration to say that transients at the start
or end of JT9/JT65 transmissions cause "large unwanted side
spectrum emissions". In fact, JT9 and JT65 signals from WSJT-X are
among the cleanest of all types on the amateur bands.
The WSJT-X waterfall intentionally uses a scale that covers a wide
dynamic range. The effective filter passbands used to produce the
waterfall are optimized for detection of signals at S/N = -30 dB, not
for steep roll-off of sidelobes.
> JT9 reception is most affected one by the strong nearby located JT
> signals, while JT65 is a bit less affected.
I do not think I have ever seen a case where reception of JT9 or JT65 is
prevented or degraded by the spectral transients you are talking about.
> There are also some side spectrum emissions that we can not avoid:
> caused by transition from one tone to other.
The mid-transmission waveforms generated in WSJT-X are as narrow as the
laws of physics permit.
Yes, the ramp-up and ramp-down at start and end of transmission could be
made a somewhat slower. Perhaps that is desirable? I have not worried
about this detail because I am not persuaded there is a significant problem.
-- Joe, K1JT
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