GRC + USRP2 + WBFM: synchronization problem?

GNU Radio
1

Hello,

I have created FM transmitter in GRC:
http://szelest.org/question/TX_RX.grc.png

Unfortunately demodulated audio has poor quality and annoying
distortions. I have spent a lot of time on it without positive effect.
Here is how demodulated audio sounds like:
http://szelest.org/question/recorded.wav

When I have created FM receiver in GRC (bottom part of the schematic),
demodulated audio sounds perfectly on my PC.
Any ideas?

I’m using gnuradio3.3.0 + USRP2(with interpolation changed from 4 to
2) + BasicTX + FT857D as hardware receiver.
GRC file: http://szelest.org/question/TX_RX.grc
input WAV: http://szelest.org/question/indiana.wav

Regards,
Marcin SQ9DJJ

2

HI,
I have installed GR on a Compaq 6715b laptop and everything seems to
work except
the GRC. When I try to run a simple test example I get the above error.

I have tried to search the internet for it, but I can not find any
reference to
it. Does anyone know what is missing?

Thanks in advance for your help,

Best regards,
Farhad

3

On 28/03/2011 4:23 PM, Farhad A. wrote:

Best regards,
Farhad

Is your PYTHONPATH configured correctly?

What platform are you running on?

Fedora? Ubuntu? Windows? Which version of the OS?

Did you install from GIT, or from a recent tarball?

Did you previously install from the distributions (ancient at this
point) pre-packaged Gnu Radio packages?

Did you follow the instructions in the Build Guide, here?

http://gnuradio.org/redmine/wiki/gnuradio/BuildGuide

4

HI Marcus,
Sorry, I should have been more clear:

  • Ubuntu 10.10
  • Install from GIT
  • Clean installation and no older packages. New Ubuntu, latest update
    and then
    Gnu Radio installed

I then choose this alternative to install:

$ mkdir build $ cd build $ …/configure $ make $ sudo make install
My PYTHONPATH is not configured, I missed it! I have to correct that.

Thanks for pointing it out.

Best regards,
Farhad

From: Marcus D. Leech [email protected]
To: [email protected]
Sent: Mon, March 28, 2011 10:34:09 PM
Subject: Re: [Discuss-gnuradio] GRC error: “ImportError: cannot import
name
wxgui”

On 28/03/2011 4:23 PM, Farhad A. wrote:
HI,

Best regards,
Farhad

Is your PYTHONPATH configured correctly?

What platform are you running on?

Fedora? Ubuntu? Windows? Which version of the OS?

Did you install from GIT, or from a recent tarball?

Did you previously install from the distributions (ancient at this
point)
pre-packaged Gnu Radio packages?

Did you follow the instructions in the Build Guide, here?

http://gnuradio.org/redmine/wiki/gnuradio/BuildGuide

5

Wav file is recorded from FT857 receiver connected directly to
microphone input of PC. Thats why its 22050Hz.

When I connect USRP2 source to the GRC receiver (bottom part of
picture) I can receive FM broadcasting.
If I connect this GRC receiver to GRC transmitter, it works perfectly
too.

Problem is that USRP2 sink connected to transmitter generates poor
signal. I don’t think that problem is connected with sample rate. I’ve
got feeling that there is problem with synchronization between GRC and
USRP2 or USRP2 is shutting frequently.

Regards,
Marcin

2011/3/29 Tom R. [email protected]:

6

On Mon, Mar 28, 2011 at 3:23 PM, Marcin Szelest
[email protected]wrote:

When I have created FM receiver in GRC (bottom part of the schematic),

You almost certainly have the sample rate set incorrectly somewhere. For
instance, when I play the file, it tells me it’s a 22050 Hz WAV file, so
something is probably set incorrectly.

Tom

7

Hello again,

I’ve fixed sampling rate for 19kHz subcarier, but problem still existed.

I found that throttle connected between WBFM and USRP2 makes situation
better.
Now I have better quality, but some disortions are still audible.

Regards,
Marcin

2011/3/30 Ed Criscuolo [email protected]:

8

Looks like you have your interpolator and your multiply blocks switched.

The way you have it, the L-R audio is interpolated up to a 200k
sample rate, and then multiplied with a 19khz subcarrier at
a 44.1k sample rate.

Do the multiply first, then interpolate the product.

Or alternately, simply change the 19 kHz sample rate to 200k.

@(^.^)@ Ed

9

On Sun, 2011-04-03 at 08:48 +0200, Marcin Szelest wrote:

Hello again,

I’ve fixed sampling rate for 19kHz subcarier, but problem still existed.

I found that throttle connected between WBFM and USRP2 makes situation better.
Now I have better quality, but some disortions are still audible.

This is a really good indication that your sample rates are off
somewhere. The throttle block should never be used when a hardware
interface is involved. Check your sample rate conversions.

–n