[Discuss-gnuradio] FW: Fwd: query about fm example file in github tutorials repository

[Jacqueline . Walker]

FWIW, I got the aforementioned “fm101.8_1Msps.cfile” to demodulate once I tried using the more generic FM demod block rather than the WBFM receive block.  I was using the rational resampler block in both cases to match the audio sink rate (48 kHz) and I did have the ‘Ok to block’ option turned off in the audio sink there too. I do have to go to some trouble to configure the audio for the ArchLinux VM I am using but it does work once I remember to  crank up the volume.

 

So the only change I made was to switch to using the FM demod block and then I could hear the demodulated fm sample file. I note that the FM demod block includes a LPF setting but I assumed that was present in the WBFM receive block? Anyway I was able to use the WBFM receive block successfully to ‘listen to’ FM radio received and streamed by a B200. Just a bit puzzled as to why it didn’t work with the streamed data file.

 

Regards

Jacqueline

 

From: Discuss-gnuradio [mailto:discuss-gnuradio-bounces+address@hidden On Behalf Of Jacqueline.Walker
Sent: 29 June 2017 20:44
To: address@hidden
Subject: [Discuss-gnuradio] Fwd: query about fm example file in github tutorials repository

 

 

 

Sent from my HTC

 

----- Forwarded message -----
From: "Jacqueline.Walker" <address@hidden>
To: "Marcus Müller" <address@hidden>
Subject: [Discuss-gnuradio] query about fm example file in github tutorials repository
Date: Thu, Jun 29, 2017 8:40 P.M.

 

OMG, silly me ...it was staring me in the face as I was laboriously typing out the filename!!

 

Thanks will try that

Regards

Jacqueline

 

Sent from my HTC

 

----- Reply message -----
From: "Marcus Müller" <address@hidden>
To: "address@hidden" <address@hidden>
Subject: [Discuss-gnuradio] query about fm example file in github tutorials repository
Date: Thu, Jun 29, 2017 6:43 P.M.

 

Hi Jacqueline,

judging from the file name (_1Msps), the sampling rate is 1 MS/s. When it comes to signal bandwidth – a complex 1MS/s stream can contain up to 1 MHz of bandwidth, but FM broadcast radio stations typically use something like 75 kHz of bandwidth for their FM signal.

Best regards,

Marcus

 

On 06/29/2017 04:39 PM, Jacqueline.Walker wrote:

Hi,

 

I downloaded the file fm101.8MHz_1Msps.cfile (from gr-tutorials/examples/tutorial6/ ) to use for trying out demodulation flowgraphs in gnuradio. It was recommended here: https://wiki.gnuradio.org/index.php/Guided_Tutorial_Hardware_Considerations

But I can’t find any details about the file – it says on the tutorial page – ‘an actual recording from a radio (USRP I presume) with nothing done to the data, so I presume it is just a binary stream such as one would receive from a USRP and that the centre frequency is 101.8MHz. What is the sample rate output by the USRP that recorded the file – is it 250k as given on the tutorial page? What is the signal bandwidth expected? I ask this because I don’t see that much on the FFT?

 

Thanks

Jacqueline

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