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

From: Andrew Rich
Subject: Re: [Discuss-gnuradio] Stuck at WBFM Project :
Date: Mon, 14 Aug 2017 02:22:56 +1000

I though decimination was throwing away samples

Like decimination of 4 is chuck away every 4 th sample

Dunno what does it mean

Can u up resample ?

And does it have to be a multiple ?


Sent from my iPhone

On 14 Aug 2017, at 2:12 am, Ash SDR <address@hidden> wrote:

Thanks everyone and sorry , I couldn't reply you all for inputs you gave me. I apologies for that... 

 For Now , I kept aside the WBFM project which I asked questions on  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..

 I am also playing around with "samp_rate" block in QT Frequency GUI Sink...  If i remove rational resampler and just pass on the signal of 1Khz with 48Khz sampling rate   in a QT GUI Frequency sink of samp_rate/4 , it outputs the signal as 0.25KHz ///. why so >

Please let me know If i am interpreting it correctly  as THIS IS VERY IMPORTANT FOR ME TO UNDERSTAND.. 



On Tue, Aug 8, 2017 at 4:41 PM, Cinaed Simson <address@hidden> 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,
and quadrature rate 192000 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


and learn something about your hardware and how to build WBFM receiver
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
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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