Re: [Discuss-gnuradio] Fwd: Problem using fm_demod.py

[Nick Harrison]

Hey Tom,

I guess "scrambled" wasn't really the best word to describe the problem. :) What I basically meant was that there was a lot of static, and I couldn't really differentiate the radio signal from the noise when I played it back. Apparently, I hadn't set up the script to the correct sampling rate, but once I got that fixed, the script worked like a charm.

Thank you!

On Fri, Jun 12, 2015 at 8:38 AM, Tom Rondeau <address@hidden> wrote:

On Thu, Jun 11, 2015 at 7:17 PM, Nick Harrison <address@hidden> wrote:

Hi everyone,

I recently started playing around with gnuradio, and being the beginner that I am, wanted to begin by listening to a close by radio station. I basically followed the instructions on http://www.trondeau.com/gr-tutorial/ and used the uhd_rx_cfile with the following command:

uhd_rx_cfile -a "addr=192.168.10.2" -g 0 -f 97.1M --samp-rate=500k -N 5000000 radio_sample_97.1Mhz.32fc

Below you can find the image of the IQ data and the PSD that I got when I used gr_plot_psd_c
http://imgur.com/kFpqK25

But when I used the fm_demod.py to playback the captured data, it comes out completely scrambled. Am I missing something here?

What do you mean by "scrambled"? That can mean a handful of different things in this domain.

Also, you set the gain to 0; you might want to increase that, though it looks like the PSD is showing a decent amount of signal.

When plotting the image the way you did, skip into the file a few thousand samples (pass -s 4000 to the gr_plot_psd_c script) to skip the start-up transients, which are obscuring the signal.

You also are bringing the signal in at 500 ksps. Make sure that the script to play back the FM signal is set up for that (it should be based on that tutorial page, but you'll want to verify).

Tom