Noob question 1

GNU Radio
1

Hello all
4 weeks ago did my first steps into Linux Ubuntu.
I am trying to get the RTL-Dongel to work but still not succeded in
that,
Time to ask some help.
There is a image with pre-installed drivers and GNU-Radio companion,
http://gnuradio.org/redmine/projects/gnuradio/wiki/GNURadioLiveDVD
I have downloaded that and put it on a USB stick. Works fine.

In the terminal I enter rtl_sdr -t and the RTL-dongel is found and it
works.
Then I start GNUradio companion, it is version 3.7.7.1. The RTL is found
in
the sources.
But the radio has a blue output and the audio-sink a orange one. In the
Help-doks it says that this is because of the datatype
but I cant change that anywhere. The dongel properties-block gives
“complex
float 32”.

Can you help me getting it to work? Only with a working system I can go
further learning.

Thanks

Henk
www.sterrenwachtleeuwarden.nl

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2

Hi Henk,

the problem is that the RTL dongle (and any SDR peripheral) just gives
you the signal as it is in the air – you will still have to demodulate
it to get audio!
Now, wild assumption: you want to listen to FM Radio for a start.
So:

  • configure your audio sink to 44100 Hz sample rate
  • use a WBFM receiver block with a quadrature rate of N*44100, and N as
    decimation, feed the output (orange!) into the audio sink
  • add a fractional resampler between source and WBFM receiver to match
    N*44100 to a sampling rate the Dongle supports

Best regards,
Marcus

3

Hooking in on the discussion here. I struggle with something similar. I
know how to work gnuradio, that’s simple enough. What i want to learn
more
about is how to configure my own SDR using gnuradio. So what the various
blocks are used for, when to use what block, etc.
I have experience LISTENING to an SDR using various devices, now i want
to
BUILD one myself.
The final objective is to learn how to decode well known signals like
the
various HAM radio protocols like PSK31, etc. I know that all has been
done
before and the easy road is to take an existing flow graph, copy it and
see
that it works. But to understand what is happening is a whole different
story.

So, without trying to hijack the thread, i am NOT looking for a gnuradio
manual, i am looking for documentation on how to USE gnuradio for signal
processing.

Thanks for the advice,

Ton.

4

My thoughts Ton,
I just made the FM receiver Marcus advised and as discribed in tutorial
6.
This week I will ask a few questions about the configuration of these
blocks.
Understanding is the key word for me.

Thanks

Henk

Op 7-9-2015 om 13:38 schreef Ton Machielsen:

5

Hi Jan
Believe me, I am reading the tutorials, also the youtube lessons

But for me it is easier to understand basics when there is a basic
working layout available. There is so much about GNURADIO
out there that a noob also needs some help with the help. (lol).

I am not a technician, developer or electronic engineer so the learning
curve is steep.

Thanks for your replay and links.

When the RTL works I will post the layout here for others.

Best regards

Henk
www.sterrenwachtleeuwarden.nl http://www.sterrenwachtleeuwarden.nl

Op 7-9-2015 om 10:47 schreef Jan Kr??mer:

6

On 09/07/2015 02:19 PM, Henk wrote:

My thoughts Ton,
I just made the FM receiver Marcus advised and as discribed in tutorial 6.
This week I will ask a few questions about the configuration of these
blocks.
Understanding is the key word for me.

Thanks

Henk

It boils down to having an understanding of DSP, which proceeds from
having an understand of signal processing in general.

There are several good books, including the works of Richard Lyons, and
Bill Sethares.

There’s also: www.dsprelated.com and www.complextoreal.com

Also, if basic RF signal-flow concepts are new to you, the first few
chapters of the ARRL handbook are quite useful, even if you aren’t
planning
to become a ham radio operator.