Parameters for APRS

[Scott Herz]

Hi everyone. I've been having a great time working with Gqrx. I have a couple questions about how to best decode APRS data with the AFSK1200 Decoder, an R820T and a 144mhz antenna. 

When APRS packets come in, it seems rather hit or miss as to if any data is going to show up in the window. Other than having it open, do I need to do anything to activate the decoder?

What settings should I use

• Does decoding APRS benefit from auto gain control? 

• I'm using Narrow FM mode with a normal filter.

• What should my gain be?

Apologies in advance if these aren't the best questions. I've only just started learning!

Thanks!

[Alexandru Csete]

On Mon, Dec 16, 2013 at 7:09 AM, Scott Herz <ceasar...@gmail.com> wrote:
> Hi everyone. I've been having a great time working with Gqrx. I have a
> couple questions about how to best decode APRS data with the AFSK1200
> Decoder, an R820T and a 144mhz antenna.
>
> When APRS packets come in, it seems rather hit or miss as to if any data is
> going to show up in the window. Other than having it open, do I need to do
> anything to activate the decoder?

No, you just open it and it is running.

>
> What settings should I use
>
> • Does decoding APRS benefit from auto gain control?
> • I'm using Narrow FM mode with a normal filter.
> • What should my gain be?

Narrow FM with normal filter is be fine. Under demod settings you can
switch off de-emphasis (set tau to off) which may improve efficiency;
however, note that APRS has very poor efficiency and requires absurdly
high SNR by todays standards.

I am also in the process of removing the built in decoder as there are
better external decoders avaialble.

Alex

[David Ranch]

Hello Alex, fellow GQRX users,

I just thought I'd chime in here.  I just spent a good chunk of the weekend updating the entire SDR sw stack on Centos6 to get Gqrx 2.2 running and the improvements from 2.1 are much appreciated!  Thanks Alex!  I'm also hoping to use Gqrx as Panadapter with Fldigi and a FT950 but its seems that the new frequency control functionality in Gqrx isn't quite suited for this fixed frequency work just yet (Gqrx should remain on a fixed frequency yet change it's displayed frequency depending on what the FT950 is tuned to).   Anyway I digress! 

I think it would be unfortunate to remove the AFSK1200 decoder from Gqrx.  I use that feature quite often as a spot checker for the local APRS and DX packet cluster frequencies.  I realize that there are now superior AFSK 1200 software TNCs now available ( for example, read the comments here http://gqrx.dk/blog/analog-bandwidth-named-gain-stages-and-a-few-ui-tweaks about Direwolf + Gqrx) but since the packet code is already present, I *personally* would like to see it stay.

Just my $0.02

--David
KI6ZHD

[grege...@gmail.com]

If you have not already done so, calibrate your R820T so that it is on frequency.  The NOAA broadcasts at 162.xxx MHz are handy for this.

[Alexandru Csete]

On Mon, Dec 16, 2013 at 5:32 PM, David Ranch <dra...@gmail.com> wrote:
>
> Hello Alex, fellow GQRX users,
>
> I just thought I'd chime in here. I just spent a good chunk of the weekend
> updating the entire SDR sw stack on Centos6 to get Gqrx 2.2 running and the
> improvements from 2.1 are much appreciated! Thanks Alex! I'm also hoping
> to use Gqrx as Panadapter with Fldigi and a FT950 but its seems that the new
> frequency control functionality in Gqrx isn't quite suited for this fixed
> frequency work just yet (Gqrx should remain on a fixed frequency yet change
> it's displayed frequency depending on what the FT950 is tuned to). Anyway
> I digress!

Hi David,

Thanks for the feedback

This situation with pandapter is a bit more tricky and requires gqrx
to be aware of the setup. I will probably look into it at some point
but I have no idea when it will be.

> I think it would be unfortunate to remove the AFSK1200 decoder from Gqrx. I
> use that feature quite often as a spot checker for the local APRS and DX
> packet cluster frequencies. I realize that there are now superior AFSK 1200
> software TNCs now available ( for example, read the comments here
> http://gqrx.dk/blog/analog-bandwidth-named-gain-stages-and-a-few-ui-tweaks
> about Direwolf + Gqrx) but since the packet code is already present, I
> *personally* would like to see it stay.

I will not remove it until there is an equally easy to use
replacement. So it could be that you have to go into the preferences
and enter a command line for multimon-ng or direwolf or
wiz-bang-over-the-top-decoder but once done you will be able to launch
it from gqrx and show the decoder output in a similar fashion as you
can today. The only difference will be that the backend will be an
external application instead of an external decoder.

Alex