Hello Phil,
.
>Igor, the whole point of playing out silence is to maintain
>synchronization. If, for example, the sampling rate is 48 kHz and your
>RTP packets each contain 240 samples (5 milliseconds), then I would
>replace a single missing packet with 240 samples of binary zeroes. Your
>signal blanks for 5 ms, but synchronization is maintained when it
>reappears. Most of the slower JT schemes wouldn't even notice.
.
We have been using correlation function to get in sync with the signal
we are going to demodulate, where evaluated delta time (DT) of candidate
signal shall match to the transmitted signal. Since we have been using
FSK modulation high accuracy of derived DT will let us to get the best SNR
of demodulated signal and will decrease number of errors prior passing
demodulated codeword to the decoder.
There are two level steps introduced in time domain if lost frames were replaced
with zero values, this steps in level can be as high as 90 dB and always making
horizontal spike line in the frequency domain, energy of this line depends on
the step value.
For instance, let's say we have got two signals being received in the same
interval, where power of one signal is 40dB higher than other one's.
We are getting one..two more wrong tones at demodulation for weaker signal
for each silence insertion, these artificial noise 'tones' shifting peak of the
correlation function bringing erroneous DT result.
There are several options to manage this error: we can try to make smooth
level transition in time domain between point A and point B where instead
of the silence. Other option is to try reconstruct time domain signal between
these points using previous/post frames as we know where there is the gap.
.
73 Igor UA3DJY
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
wsjt-devel mailing list
wsjt-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/wsjt-devel
