Hi Stephan,
so how do you get the samples into GNU Radio?
I guess you use the gr-osmosdr source?
What does your flow graph look like?
Best regards,
Marcus
On 06/02/2015 12:04 AM, Stephan van
Beerschoten wrote:
I am sure GR can do that, but I can't ;-)
Also, I don't have a good waterfall at all of the pocsag
broadcast, which is probably part of why I can't make it out
with my ears either. Yes, I think I have too much noise.
I hope it can be overcome with the right settings and filters.
I'll try to capture a screenshot of what I see. It's
nothing like the screenshots in Wikipedia.
On Jun 1, 2015 5:47 PM, "Marcus Müller"
< address@hidden>
wrote:
Hi!
I personally think the soundbite from wikipedia is broken,
since it's 11kHz sampling rate violates Nyquist ;)
Well, I must admit that my preferred way of analyzing this
wouldn't be the audible reproduction; if you can see it
clearly on the waterfall, and "optically" have enough dB
between the carriers and noise, then you'll be fine decoding
it.
Now, I trust you're actually seeing excessive noise -- this
might point to problems with your receiver (unsuitable
antenna, too much noise in the amplifier, too little gain,
intermodulation). The first step in limiting noise is always
adding appropriate filtering. Can you add a FIR that selects
your POCSAG channel out of your sampling bandwidth?
Best regards,
Marcus
On 06/01/2015 11:28 PM, Stephan van Beerschoten wrote:
You're right in that I need more than GR. The
audio of a pocsag broadcast is very distinct. It's also
clearly visible on a waterfall.
The problem is that I have too much static in there. Way
too much noise. I can't get the gqrx module (where I
tune and see the waterfall) set right so the reception
is fine.
I think the Wikipedia article had a soundbite of a
pocsag encoding. If you listen to it you'll notice it's
very distinct.i just have 90% noise and I can hear the
broadcast in the very background.
On Jun 1, 2015 5:25 PM, "Marcus
Müller" < address@hidden>
wrote:
Hi again,
Ok, I'm not familiar with the standard POCSAG, but
if you got a signal that you still need to decode
with something else, how do you know you don't get
clear reception? What is your measure for "good
reception"?
As far as I read the English wikipedia, POCSAC uses
a 4.5kHz binary FSK, so can you see the two
alternating frequency e.g. in a waterfall plot of
your RX signal?
Ideally, you'd directly be able to see the 512, 1200
or 2400 baud.
To explain a bit more:
GNU Radio is not a decoder for any specific
standard; think of it as the LEGO of SDR. You can
build amazing things with it, in fact, there's a lot
of examples that come with GNU Radio, and useful and
complex standard implementations (FM receiver, DTV
transmission!), but if you need to have something
that's not there, you might need to a) use someone
else's Out-Of-Tree module or b) implement that
functionality yourself. So I must admit that I don't
have the slightest idea which settings you're
referring to :) Maybe you're interested in a
quick&dirty introduction to GNU Radio [1].
In the case of POCSAG, I remember gr-pocsag being a
thing (search for pocsag on cgran.org); I can't remember
the original author, and I presume it's pretty much
dead -- but I'd love to be proven wrong.
Also, pyboms has pocsag-mrt package, but that seems
to rely on GNU Radio 3.6.2, if the Readme is
correct, so that's pretty dead, too.
Best regards,
Marcus
[1] https://github.com/iZsh/pocsag-mrt
On 06/01/2015 10:18 PM, Stephan van Beerschoten
wrote:
It is. I plan on running the output
through a utility that can decode it. However,
before that can happen I need to find out how I
can get a clear reception of the broadcast.
On Jun 1, 2015 4:15 PM,
"Marcus Müller" < address@hidden>
wrote:
I'm a bit confused, I
though POCSAG was a text pager system?
On 06/01/2015 10:04 PM, Stephan van
Beerschoten wrote:
> Hi Guys,
>
> I compiled gnuradio for my ODROID ARM
platform, and I can listen to
> regular wideband radio just fine. I am
using a Generic RTL2832U with
> Rafael Micro R820T tuner.
>
> The radio quality is fine, and even when
using the rtl_fm tool
> directly (off topic for this list), it
works.
>
> However, when I switch channels to
155.520 to capture POCSAG
> broadcasts I cannot get a clear
reception. I can't find any decent
> documentation on GR to tell me what each
setting is, and I am not a
> HAM radio operator so some of the basics
evade me.
>
> I can't get decent POCSAG reception with
the rtl_fm tool either, so
> this is probably a setting thing
somewhere.
>
> Why can't I get clear reception? Any
pointers?
>
> Stephan
>
>
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