LF: Re: [rsgb-lf-group] SlowJT9 update (v0.9.15.0)

[N1BUG <paul@n1bug.com>]

Hello Rik, all,

Two comments, see below.

> Interestingly Rik's SlowJT9 which was running in parallel,
> managed to decode a couple of more transmissions than WSJT-X."

I have seen this work both ways. Sometimes SlowJT9 will decode
something WSJT-X does not. Other times WSJT-X will decode something
SlowJT9 does not. Usually they are equal.

> 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.

I think there is justification for it on 2200m if it comes without
too high cost in lost sensitivity. Some people cannot easily tune
antennas down to 136.4 or so. But if we operate at 137.x then
listening stations must adjust their receiver because the usual
136.000 'dial' frequency will not allow receiving JT9-5 or JT9-10.
This is not the usual setting for most who also want to monitor WSPR
or other modes. For pre-arranged QSOs this will not matter, but for
calling CQ it is good to operate where we can be heard without
special receiver settings.

However, if this feature comes with significant loss of decoding
sensitivity, then I would vote to stay as we are.

73,
Paul N1BUG