Re: [Discuss-gnuradio] USRP2 FM TX and FM RX working together

[Rafael Diniz]

Hi Jorge,
Can you copy the .grc file you created?

> Hello community!
>
> I initiated myself in GNU radio two weeks ago and I am learning as fast as
> I
> can. To begin with, I decided to play with GRC and my URSP2.
> I successfully built a FM modulator that works fine.
> I successfully built a FM demodulator that works fine.
> But there are still several things I do not understand.
>
> While building the FM modulator:
> 1)Wave file source
> 2)Rational resampler
> 3)LPF
> 4)Rational resampler
> 5)Frequency Mod
> 6)Multiply const
> 7)USRP2 sink
>
> Why is block 6 necessary? I tried with lots of values over 2 and all of
> them
> are ok. I realized that the smaller the number, the higher the noise in my
> receiver (my mobile phone). Is it related to the amplitude of the
> modulated
> signal?
>
> Another thing very strange is that if I create a GRC file with both,
> transmitter and receiver with exactly the same blocks and the same
> parameters I cannot hear any demodulated signal. I can see information
> with
> a FFT block connected to the receiver chain, and I am able to demodulate
> the
> signal with my mobile phone when the example is running but in my computer
> I
> do not hear anything else besides noise mixed with some sort of
> non-understandable signal. Thus, I guess I have to change something in the
> receiver chain although it works alone in my FM demodulator. I changed
> every
> single parameter but I cannot get any improvement.
>
> Any suggestions?
>
> Many thanks in advance,
> Jorge.