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

 From: Anon Lister Subject: Re: [Discuss-gnuradio] Stuck at WBFM Project : Date: Sun, 13 Aug 2017 16:59:14 -0400

Idk if anyone mentioned, but things like samp_rate are just variables, they do not propegate through the flowgraph and change based on the blocks they go through. The flowgraph doesn't attach special meaning to samp_rate, it's just a default param in alot of blocks. You could call it AshesFavVariable and the flowgraph would work the same. In your case I think the sinks are just defined to be samp_rate, so they will display whatever you set samp_rate to be. Ideally you'd make a decimation variable, set it to say 4, the set the Sample Rate parameter on downstream blocks to samp_rate/decimation.

On Aug 13, 2017 12:15 PM, "Ash SDR" <address@hidden> wrote:
Thanks everyone and sorry , I couldn't reply you all for inputs you gave me.  For Now , I kept aside the WBFM project which I asked about and working on the Guided Tutorials from GNU Radio and also tutorials from greatScott gadgets video series.

I have a dumb question about Rational Resampler...    Here is the snapshot from tutorials website..

As far as I understand , the Rational resampler  modifies the sampling rate of the incoming signal based on Interpolation (or) decimation factor....  Is it something like this

If my incoming Signal is of 10KHz  with Sampling Rate of 50 KHz  ,  Rational Resampler (Interpolation : 4 , Decimation : 1)  gives me the output as signal of 10KHz and Sample Rate of 50*4 = 200 KHz         ??????

Am I Interpreting it correctly... ??????

If thats the case , In the following snapshot ,  Signal of 1KHz of 48KHz Sample rate is interpolated by factor 4 ,   Then Output Sampling Rate should be 48*4 = 192KHz which is much higher than the Required Nyquist rate , But the Frequency sink block shows frequency component at 0.25 Hz... Is it because of the "samp_rate" variable set in QT GUI Frequency Sink..

On Tue, Aug 8, 2017 at 4:41 PM, Cinaed Simson wrote:
On 08/07/2017 07:55 PM, 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 ?

Remove the first rational resampler. Set your audio rate to 48000 Hz,

In the second re-sampler set the interpolation to 8000000 Hz and the
decimation to 192000 Hz.

I'm going to guess you're using the HackRF based on your default values
(except for the transmit RF gain which should be 1.)

I strongly recommend you spend some time on the going through the
tutorials at

befor you try to transmit.

-- Cinaed

>
>
> 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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