Hi Bill and Charlie,
In r8389 I’ve attempted to improve the calibration of JT65 VHF/UHF/Microwave
SNR estimation. It looks like Joe may have originally tuned the SNR estimates
for the large Doppler spread/JT65C cases. I’ve switched it around a bit to
favor small to moderate Doppler spreads. In any case, accuracy will depend on
mode, Doppler spread, and SNR. Feel free to let me know if you identify a set
of conditions where the calibration is particularly inaccurate.
Question for Bill - how come the whole file (jt65sim.for) shows as changed in
r8388?
Steve k9an
> On Jan 1, 2018, at 4:05 PM, Bill Somerville <[email protected]> wrote:
>
> On 01/01/2018 20:41, Bill Somerville wrote:
>> On 01/01/2018 17:56, Steven Franke wrote:
>>> Hi Charlie,
>>>
>>>> Does anyone know how to batch process a number of files (in Audacity or
>>>> something else) to a) amplify them and b) convert from 12000 to 11025.
>>> I have used sox and bash shell scripts to do the type of work that you have
>>> described.
>>>
>>> I will look at the JT65 VHF/UHF/Microwave SNR estimate to see if I can
>>> tweak it to reduce the bias at low SNRs. (A different estimate is used for
>>> HF operation).
>>>
>>> BTW, I note that your single example from WSJT suggests that it may have an
>>> even larger bias, of the opposite sign.
>>>
>>> Steve k9an
>> Hi Charlie and Steve,
>>
>> it seems to me that the easiest thing to do here is modify jt65sim to be
>> able to generate 11025 Hz sample rate .WAV files as well as 12000 Hz. I have
>> done this but cannot get WSJT to decode them. WSJT-X decodes them fine using
>> it's automatic sample rate converter. When I work out why WSJT is not
>> decoding them I will check in the updates to jt65sim.
>>
>> 73 and HNY
>> Bill
>> G4WJS.
>>
>
> Hi Steve & Charlie,
>
> I have got WSJT reading the simulated files. WSJT needs a fairly hefty
> positive gain offset applied to the PCM stream, around +30dB seems about
> right. I have added the following new command line options for jt65sim:
>
> >\build\wsjtx-dev\Debug\jt65sim -h
>
> Usage: jt65sim [OPTIONS]
>
> Generate one or more simulated JT65 signals in .WAV file(s)
>
> Example: jt65sim -m B -n 10 -d 0.2 -s \\-24.5 -t 0.0 -f 4
>
> OPTIONS: NB Use \ (\\ on *nix shells) to escape -ve arguments
>
> -h
> --help
> Display this help message
> -m MODE
> --sub-mode MODE
> sub mode, default MODE=A
> -n SIGNALS
> --num-sigs SIGNALS
> number of signals per file, default SIGNALS=10
> -F F0
> --f0 F0
> base frequency offset, default F0=1500.0
> -d SPREAD
> --doppler-spread SPREAD
> Doppler spread, default SPREAD=0.0
> -t SECONDS
> --time-offset SECONDS
> Time delta, default SECONDS=0.0
> -f FILES
> --num-files FILES
> Number of files to generate, default FILES=1
> -p
> --no-prng-seed
> Do not seed PRNGs (use for reproducible tests)
> -s SNR
> --strength SNR
> S/N in dB (2500Hz reference b/w), default SNR=0
> -S
> --11025
> Generate at 11025Hz sample rate, default 12000Hz
> -G GAIN
> --gain-offset GAIN
> Gain offset in dB, default GAIN=0dB
> -M Message
> --message Message
> Message text
> where:
>
> --f0 n (or -F n) sets the base frequency of the generated signal(s), default
> 1500.0 Hz,
>
> --11025 (-S for slow) generate a 11025 Hz sample rate,
>
> --gain-offset n (or -G n) sets the overall gain offset applied to the
> generated signal output, default is 0dB.
>
> Steve, I am unsure about a couple of the changes I have made, particularly
> the limited slice of the cdat complex array used when applying the Rayleigh
> fading model on line 275 (necessary to avoid an array bounds violation when
> using 11025 Hz rate), and whether I should apply clipping to 16-bit full
> scale after applying the gain offset at line 288. I also don't understand
> what line 287 is doing as it seems to apply a normalization factor 'fac' that
> I would expect to be applied on line 288 yet that line used a fixed factor of
> 100.0 (`rms`). Perhaps you can review my changes and advise?
>
> Charlie, I don't know what version of jt65sim you are using, you OP document
> above shows a command line that probably matches a very old version. The
> current version, which is not shipped in the installer, takes the above
> command line options and switches. I used it like:
>
> >\build\wsjtx-dev\Debug\jt65sim -M "G3WDG G4WJS -20" -f 10 -n 1 -t 2.5 -m C
> >-S -F 1227.5 -s \-10.0 -G 30.0
> for JT65C at 11025 Hz suitable for WSJT, and like this:
>
> >\build\wsjtx-dev\Debug\jt65sim -M "G3WDG G4WJS -20" -f 10 -n 1 -t 2.5 -m C
> >-s \-10.0
> for a similar simulation suitable for WSJT-X.
>
> 73
> Bill
> G4WJS.
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