Dear all,
Beta-release v0.9.15.0 of SlowJT9 has been uploaded, see
http://www.472khz.org/SlowJT9/.
Changes:
- PSKreporter.info spotting added.
- Flexible frequency boundaries for the spectrum display added (100 - 5000 Hz in 100 Hz steps).
- Help file added.
Bug reports, remarks and suggestions are welcome.
Next on my to-do list:
1. Run the recorded audio several times through the decoder with small "time-shift" steps.
I was intrigued by a mail from David, G0MRF, (17 Januari):
"Last night was very good for propagation and TA activity on 630m.
It was one of those rare nights where signals were at a reasonable to good level, but unlike
the previous several days, if not weeks, QSB was remarkably slow with only a few dB between peaks and troughs. There was a period between 02.00 and 04.00 with no decodes here, but between 06:25 and 07:49 I decoded 19 transmissions from K9KFR in EN77, most
of which were CQs
I was pleased to work Glenn VE9GJ on JT9 shortly after he made his first TA QSO with Jan
LA3EQ.
Interestingly Rik's SlowJT9 which was running in parallel, managed to decode a couple
of more transmissions than WSJT-X."
As I use the JT9 decoder from the WSJT-X suite the performance of SlowJT9 and WSJT-X should be identical. The only difference between both could be a small timing difference that made SlowJT9 to decode some extra transmissions (pure luck, it could have been
the other way around as well).
So maybe the performance of SlowJT9 can be improved by running the recorded audio several times through the decoder with each time a small (0.1 second ?) time shift induced in the audio and then taking a "best off" all decoded signals.
I am not sure it will really help, but it seems worth to try.
2. Add optional internal frequency conversion to allow reception at higher frequencies
I have done some preliminary tests (based on the code snippet Wolf, DL4YHF, sent me) and it seems to work fine.
But I am not sure that it will be very useful as frequency conversion will not increase the usable frequeny range, but just shit it.
Eg: now JT9-10 can be received from 100 Hz to 415 Hz audio. After USB downconversion with a 1 kHz carrier the range will be 1100 Hz to 1415 Hz.
The only reason I can think of to want frequency conversion is if you use a fixed frequency (ofen 800Hz) CW filter, so you can fit the JT9-5 or JT9-10 frequency range into the filter passband.
But this downconversion requires a Hilbert transform (90 degrees all pass filter) that never can be perfect and this will cause some distortion (in particular at the lower and of the passband).
So before I start the effort to implement this in SlowJT9 I would like to know if there is an audience for it.
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