Enabling AFSK1200 decoder stops AF recording?

[David Ranch]

Recording was going well until I opened the very useful AFSK1200 baud decoder window:

-rw-rw-r-- 1 dranch dranch 59064320 Aug  9 20:25 /home/dranch/gqrx_20160810_032039_145630000.wav
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-rw-rw-r-- 1 dranch dranch 95555584 Aug  9 20:28 /home/dranch/gqrx_20160810_032039_145630000.wav

Gqrx still showed it's recording (button is presessed in) but it stopped updating the file:

-rw-rw-r-- 1 dranch dranch 96399692 Aug  9 20:29 /home/dranch/gqrx_20160810_032039_145630000.wav
-rw-rw-r-- 1 dranch dranch 96399692 Aug  9 20:29 /home/dranch/gqrx_20160810_032039_145630000.wav
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-rw-rw-r-- 1 dranch dranch 96399692 Aug  9 20:29 /home/dranch/gqrx_20160810_032039_145630000.wav
-rw-rw-r-- 1 dranch dranch 96399692 Aug  9 20:29 /home/dranch/gqrx_20160810_032039_145630000.wav
-rw-rw-r-- 1 dranch dranch 96399692 Aug  9 20:29 /home/dranch/gqrx_20160810_032039_145630000.wav
-rw-rw-r-- 1 dranch dranch 96399692 Aug  9 20:29 /home/dranch/gqrx_20160810_032039_145630000.wav
-rw-rw-r-- 1 dranch dranch 96399692 Aug  9 20:29 /home/dranch/gqrx_20160810_032039_145630000.wav
-rw-rw-r-- 1 dranch dranch 96399692 Aug  9 20:29 /home/dranch/gqrx_20160810_032039_145630000.wav

It was decoding 1200baud packets  Once I then clicked on the AF record button to stop it recording and clicked on REC again to start recording, it then stopped decoding AFSK1200 packets.  Are these two features incompatible running at the same time?

--David
KI6ZHD

[Alexandru Csete]

On Wed, Aug 10, 2016 at 6:55 AM, David Ranch <dra...@gmail.com> wrote:
>
> Recording was going well until I opened the very useful AFSK1200 baud
> decoder window:
>

> ...

>
> It was decoding 1200baud packets Once I then clicked on the AF record
> button to stop it recording and clicked on REC again to start recording, it
> then stopped decoding AFSK1200 packets. Are these two features incompatible
> running at the same time?

Hi David,

It's most certainly a bug; however, the built in afsk decoder has been
broken for a long time, so I'm surprised that it is still working for
you in any way.

Today there is a much, much better decoder available in direwolf. It
can even interface directly to gqrx through the UDP interface.
Hopefully you can use that instead.

Alex

[David Ranch]

Hello Alex,

I'm not sure why you say the AFSK1200 decoder is broken.. it seems to work quite well for strong signals and the more important point, it's super convenient to have that display in a Gqrx window!  With that said, yes, I'm also a big fan and user of Direwolf and run it every day but when using Gqrx, I prefer to use it's native decoder for it's convenience and easy readability.   I would really hate to see this functionality in Gqrx to go away.

Anyway, should I file a ticket for this issue against the version of Gqrx I'm running (gqrx-2.5.3-1.20160307git8bbe051d)?  This combination of features is really useful to me.  The only other thing I could ask for is the ability to maybe enable/disable the de-emphasis code to better emulate listening to a radio's signal listening at the discriminator point (aka.. 9600 baud data port).  Maybe that's worth another ticket?

--David
KI6ZHD

[Alexandru Csete]

On Wed, Aug 10, 2016 at 6:27 PM, David Ranch <dra...@gmail.com> wrote:
>
> Anyway, should I file a ticket for this issue against the version of Gqrx
> I'm running (gqrx-2.5.3-1.20160307git8bbe051d)?

Well, yes, it might increase the chances of it getting fixed.

> The only other thing I could ask for is
> the ability to maybe enable/disable the de-emphasis code to better emulate
> listening to a radio's signal listening at the discriminator point (aka..
> 9600 baud data port). Maybe that's worth another ticket?

You can switch off de-emphasis under demodulator options, set Tau =
Off. Unfortunately, it is not a setting that is restored at then next
session.

Alex

[David Ranch]

Ok.. Github issue filed.  As for the de-emphasis point.. wow.. thanks for that.  I didn't think to look at the "..." button.  Maybe that could be relabeled something like "Opts" to be a bit more intuitive?   Beyond that, I'm going to have to research how a parameter with units like microseconds map to functionality like pre-emphasis!   Maybe you have a good URL you'd recommend to start off with?

--David

[Greg Troxel]

For starters:

https://en.wikipedia.org/wiki/Emphasis_(telecommunications)
http://www.sengpielaudio.com/calculator-timeconstant.htm

[David Ranch]

Ah... I really like that to the point sengpielaudio URL with lookup tables and more.  Thanks so much Greg!

--David
KI6ZHD

[Robin Gape]

Comments in-line:

On 11/08/16 05:21, David Ranch wrote:

Ok.. Github issue filed.  As for the de-emphasis point.. wow.. thanks for that.  I didn't think to look at the "..." button.  Maybe that could be relabeled something like "Opts" to be a bit more intuitive?

Had one been paying attention in English class—if one might be so bold as to suggest—then the use of ellipsis (…) as indicating something missing or that there is something more, as yet unsaid, might have been clear. That asserted, there are few ellipses of the punctuation sort to be found in technical books or similar material. They are far more likely to be found in novels or similar writing. [Note: a good engineer is a master or mistress of all the arts!]

Beyond that, I'm going to have to research how a parameter with units like microseconds map to functionality like pre-emphasis!   Maybe you have a good URL you'd recommend to start off with?

The amount of pre-emphasis is defined by a time constant, as Greg and Alex noted. In the Amateur Service, there is an IARU Region 1 recommendation for NBFM speech of a speech bandwidth of 300Hz-3kHz, with 6dB/octave pre-emphasis. Assuming a turnover frequency of 300 Hz, the corresponding time constant (𝜏) is 1/(300×2π)≈530µs. In essence, what is called NBFM is really NBPM, narrow band phase modulation.

--David

HTH

Robin, G8DQX