Remote toggle DSP / headless

[Hanns Holger Rutz]

Hi there,

I'm quite new to SDR; I want to use gqrx for a sound installation where
it is remote controlled to set frequencies and record audio snippets
from time to time. I played around with the telnet things, and so far
this seems to work great, thanks!

I have one big issue, though; the installation computer (this will be a
raspberry pi 3) will run everything automatically, there is no GUI
interaction. It appears that gqrx doesn't remember the DSP toggle
setting, and I only get failure (RPRT 1) when trying to `U RECORD 1`
while the DSP is off. When gqrx is started, the DSP is always off.

So is there a way to enable DSP at startup time? Or is there a remote
command to do so?

Another question is: Is it possible to disable the waterfall display to
minimise CPU usage.

I'm running Raspbian Jessie (not lite).

Thanks!

Best, .h.h.

[Simon Kennedy]

Hi .h.h.

the reality is that gqrx is a graphical application. As far as I remember there is no way to start it with DSP on nor to disable the waterfall.

You don't say which SDR device you are going to use but it sounds like a command line program would be more appropriate for your particular installation. If you are using an RTL device you could try rtl_fm For more complexity you might need to call rtl_fm or GNUradio Companion (GRC) Python code in a wrapper program using e.g. Python. 

HTH

Simon.

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[Hanns Holger Rutz]

hi simon,

yes, I'm using some USB stick called 'NooElec', it shows up as 'Realtek,
RTL2838UHIDIR'.

I tried rtl_fm, but neither does it select to correct frequencies (seems
always of a few percent), nor does it produce a clean signal, even when
I manage to get the right frequencies; gqrx in contrast gets quite good
audio quality. So unless I understand why rtl_fm doesn't work correctly,
I will have to stick to gqrx.

For example, I have an FM station at 95.4 MHz that I can listen to in
gqrx using normal filter width wide FM mono. I would think the
equivalent in rtl_fm is

rtl_fm -f 95200000 -M wbfm -s 48000 ~/Music/test.raw

Still that is extremely noisy. (I actually have to use -f 95132000 so
the program sets 95.2 MHz).

Best, .h.h.

On 11/10/17 14:08, Simon Kennedy wrote:
> Hi .h.h.
>
> the reality is that gqrx is a graphical application. As far as I
> remember there is no way to start it with DSP on nor to disable the
> waterfall.
>
> You don't say which SDR device you are going to use but it sounds like a
> command line program would be more appropriate for your particular
> installation. If you are using an RTL device you could try rtl_fm

> <http://kmkeen.com/rtl-demod-guide/> For more complexity you might need

> to call rtl_fm or GNUradio Companion (GRC) Python code in a wrapper
> program using e.g. Python. 
>
> HTH
> Simon.
>
> On 11 October 2017 at 12:47, Hanns Holger Rutz <con...@sciss.de

> <mailto:con...@sciss.de>> wrote:
>
> Hi there,
>
> I'm quite new to SDR; I want to use gqrx for a sound installation where
> it is remote controlled to set frequencies and record audio snippets
> from time to time. I played around with the telnet things, and so far
> this seems to work great, thanks!
>
> I have one big issue, though; the installation computer (this will be a
> raspberry pi 3) will run everything automatically, there is no GUI
> interaction. It appears that gqrx doesn't remember the DSP toggle
> setting, and I only get failure (RPRT 1) when trying to `U RECORD 1`
> while the DSP is off. When gqrx is started, the DSP is always off.
>
> So is there a way to enable DSP at startup time? Or is there a remote
> command to do so?
>
> Another question is: Is it possible to disable the waterfall display to
> minimise CPU usage.
>
> I'm running Raspbian Jessie (not lite).
>
> Thanks!
>
> Best, .h.h.
>
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> <https://groups.google.com/d/msgid/gqrx/fd0c8dc5-5063-b508-b298-54d7cba4a342%40sciss.de>.

> For more options, visit https://groups.google.com/d/optout

> <https://groups.google.com/d/optout>.

>
>
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[Hanns Holger Rutz]

ok, some idea:

xdotool search --name 'Gqrx 2.6' windowactivate key ctrl+d

this seems to do the trick on my desktop stretch, haven't tried yet on
the pi.

best, .h.h.

[Simon Kennedy]

Hi .h.h.

in rtl_fm you need to use the -p <error> option to adjust for the frequency error. The same option is available in gqrx in the box called Freq. Correction. To get my RTL tuner onto frequency I have to use a correction of -10 ppm.

You also need to set the sample rate to the bandwidth of the signal you are receiving. I don't know the actual width of an FM signal but 200k works massively better than 48k (which is too narrow).

e.g.

rtl_fm -f 96400000 -p -10 -M wbfm -s 200000 | play -r 32k -t raw -e s -b 16 -c 1 -V1 -

Regards

Simon.

[Thomas Trummer]

Hi,

I have tried the GQRX software today It is really amazing, thanks. It works great on my rpi3 and RTL-SDR stick.

There is only one thing missing for me. I also need a way to Start/Stop the DSP over the romet interface.

Is this a feature which will come in the next version?

Thanks

Thomas