Re: [Discuss-gnuradio] Fwd: Problem with getting clear FM signals using

First 100k is insufficient sample rate from the E110. An FM station has 150 kHz total swing (+/- 75 kHz) so the frequency range of your E110 complex output is 100 kHz and is therefore insufficient for the entire modulation. You then feed the 100k sample per second signal into the FM block where you have informed it you will be sending 500 kHz (quadrature rate) and then with no decimation at all, you send the 500 kHz sample rate detected audio to a sound block where you've told it to expect 96 kHz audio.

$\left [ 0.9 \left [ \frac{A+B}{2} + \frac{A-B}{2}\sin4\pi f_pt \right ] + 0.1\sin2\pi f_pt \right ] \times 75~\mathrm{kHz}$

is the instantaneous frequency of an FM stereo broadcast signal where A is the left channel, B is the right channel and fp is the pilot tone frequency (19 kHz).

Consider matching sample rates between these blocks as the software defined radio equivalent of "impedance matching" between analog circuits in one view of it.

Bob

On Wed, Apr 9, 2014 at 7:40 AM, Mike Jameson <address@hidden> wrote:

Here are some pointers for you:

- Firstly, your screenshot shows the error message saying that the RX frequency is not valid. I'd recommend using a WBX daughterboard, however the BasicRX should still work with strong FM signals with aliasing if that is what you are using.

- The samp_rate is set to 100e3. It should be the master clock rate of the e110 divided by an even number such as 64e6/256 (250e3).
- The quadrature rate in the WBFM receive block should be set to samp_rate (250e3) and the Audio decimation should be set to 5.

- The audio sink sample rate should be set to samp_rate/audio_decim (250e3/5=50e3). 50e3 is as close to the wanted audio sample rate of 48e3 that you are going to get without using one of the resampler blocks.

Mike

--
Mike Jameson M0MIK BSc MIET
Email: address@hidden
Web: http://scanoo.com

---------- Forwarded message ----------
From: Abouda Yassine <address@hidden>
Date: Wed, Apr 9, 2014 at 12:09 PM
Subject: Re: [Discuss-gnuradio] Problem with getting clear FM signals using the usrp e110
To: Mike Jameson <address@hidden>

hi Mike,

thx for offering help.I enclosed both a picture of the fm receiver and the grc file(because i'm using the embedded gnuradio version on the usrpe 110),so it might not open correctly to you.I will be waiting for your answer.

2014-04-09 11:47 GMT+02:00 Mike Jameson <address@hidden>:

Abouda,

If you attach your GRC file to your reply I'll take a look at it for you. It sounds like a sample rate mis-match going on somewhere.

Mike

--
Mike Jameson M0MIK BSc MIET
Email: address@hidden
Web: http://scanoo.com

On Tue, Apr 8, 2014 at 12:18 PM, Abouda Yassine <address@hidden> wrote:

Hello,
I followed this tutorial to build a simple FM receiver: https://www.youtube.com/watch?v=KWeY2yqwVA0.I am using the USRP e110,my problem is I am only getting noise.I tried to change blocks and parameters and it worked for me when I deleted the rational resampler and made a 100k as a sample_rate parameter.I get to hear FM radio stations but the quality of the sound is very bad it's like on the SAW movie.Any one has a solution on how to improve the sound quality!!!!thx

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Bob McGwier
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From:	Robert McGwier
Subject:	Re: [Discuss-gnuradio] Fwd: Problem with getting clear FM signals using the usrp e110
Date:	Wed, 9 Apr 2014 08:55:57 -0400