Re: [Discuss-gnuradio] Stuck at WBFM Project :

Hi Ash,

This might be a bit of a DSP problem more than a GNU Radio-specific one!
So, you have this wave file that was sampled at 48 kHz. Then you interpolate it by 20 – so, now, if you follow that logic, that stream is /meant/ to represent an audio signal sampled at 960 kHz. Now, after that, you parameterize the WBFM as if the signal was 400 kHz, and have a 1:1 input/output rate (that's what's important for my argument).

So, you have what's meant to be 960 kHz, and then you interpolate it again, by 20, to a signal that is meant to be sampled at 19200 kHz = 19.2 MHz. Then you go ahead and "play back" that signal with a hardware device through the Osmocom sink, but at 8 MS/s – so, everything transmitted is played back at /less than half speed/!

I don't really understand what your motivation with the specific parameterizations of the two (that's definitely one too many) resamplers, or the WBFM was, but you should probably just take a step back, and ask yourself "what does this block do?" for /every/ block. This flow graph looks like it is a random combination of tutorials and Youtube videos – that's not how engineering works ;). (By the way, there's other things wrong with the flow graph, but since it needs a bit of restructuring anyways, I'm not going to address those here)

If you haven't, I'd strongly recommend reading the "Guided Tutorial" on

https://tutorials.gnuradio.org

It doesn't specifically address the sampling rate confusion you were a victim of, but it does (hopefully) give you a bit of a feeling about what generally happens, so I think this is the very most time-efficient method of approaching GNU Radio.

Hey, and keep up the good work! Starting into SDR is always a bit of a rocky path, because you need a threefold set of talents – Radio, Software, and Signal Processing. Don't be demotivated if things don't work right off the start!

To help you with your application: Remember, a Resampler has a non-1 (output rate)/(input rate) ratio. In case of the rational resampler, that ratio is (interpolation)/(decimation)

What about

Wav File Source -> WBFM (audio rate 48k, quadrature rate 192k) -> Rational Resampler (interp/decim=(Osmocom sink sampling rate)/(192k)) -> Osmocom sink

Best regards,

Marcus

On 08/08/2017 04:55 AM, Ash SDR wrote:

Hello Everyone ,

I am a GNU Radio beginner trying to implement Wideband FM Project and transmit it to my FM receiver at a very lower power.  I am choosing a frequency in a FM band such that my receiver is not picking anything from that station/..

Attached is GRC file which i am working on .and the music file which i am trying to transmit..

Can anyone please tell me where I am messing up ?

As a beginner , my learning curve is from implemented projects , University lectures which are available on-line .. This one is from a book which i am using to get basic understanding ..

Thanks

Ash

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