Re: [Discuss-gnuradio] CPFSK mod/demod + strange behavior

[Tomaž Šolc]

On 08. 06. 2016 14:59, Olivier Goyette wrote:
> 1st concern : when I enable the rational resampler with
> Interpolation set to : baud_rate and Decimation set to : sample_rate,
> GRC seems to not execute the flowgraph at all as if the calculations
> were too big ?! Since *sample_rate* / *baud_rate* =
> *sample_per_symbol*s, I tried to put Interpolation to 1 and
> Decimation to 6, but GRC freezes for about a minute after execution
> of the flowgraph. So, what should I do to keep my parameters valid if
> I really need to use a rational resampler block?

If I understand you correctly, I think you don't need the "Rational
Resampler" block at all.

Your "USRP Sink" consumes samples with the rate of 6.25M/s.

You have a "CPFSK" block that produces 6 samples per each input bit,
which gives you 6.25M/s / 6 = 1.041667M/s bitrate without any kind of
resampling.

> In this application, the fsk_deviation_hz shall be +312.5K for a '1'
> and -312.5K for a '0'. How may I be sure to respect this
> specification by using the CPFSK block ?

If you check the source for the CPFSK, you'll see that it advances the
phase of the signal by +/- k * pi for each symbol. From that you can get
the following formula:

k = 312.5k * 2 / 1.041667M = 0.6

so it seems you already have that correctly set up.

Best regards
Tomaž