Hi Joe, Bill and All,
In the latest WSJT-X release we still have large unwanted side spectrum
emissions at beginning and end of the message transmission.
JT9 reception is most affected one by the strong nearby located JT signals,
while JT65 is a bit less affected.
There are also some side spectrum emissions that we can not avoid: caused by
transition from one tone to other.
Playing with amplitude fading at the end of transmission we can reduce side
emissions so that side spectrum width will be only three times larger than tone
transition's one.
It is achieved by these values in Modulator.cpp source code:
Line 221 i0=(m_symbolsLength - 0.034) * 4.0 * m_nsps; // increasing tail length
twice
Line 262 if (m_ic > i0) m_amp = 0.99 * m_amp; // slower fading
Sreenshot with the achieved spectrum and WAV file are attached and also there:
https://cloud.mail.ru/public/L2MH/51XfCmJRP
For beginnig of the message (first tone) we need to apply reversed exponential
function for slow amplitude increase, the same number of samples as for the end
of message.
Due to the complexity of Modulator.cpp usage for various modes and my little
CPP knowledge I can not propose exact changes in the code for the first tone.
May I ask to consider these changes for Modulator.cpp source code in some
future WSJT-X release, please?
73 Igor UA3DJY
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