Re: creating a 57 KHz signal from 19 KHz reference

[Kristoff]

Hi Andy,


I played around with this some more yesterday.


On 15/11/19 18:16, Andy Walls wrote:
> > From:   Kristoff
> > Date:   Thu, 14 Nov 2019 23:39:32 +0100
> [snip]
>
> > Question:
> >
> > I am trying to find a way to use the 19 KHz stereo-pilot signal to
> > create a 57 KHz carrier (to down-convert the FM/RDS carrier at 57
> > KHz).
> >
> > How do I do this?
> Use the PLL carrier tracking block which will simultaneously:
>
> 1) phase lock to the 19 kHz pilot tone
> 2) shift (in reality rotate) the spectrum of the signal so the 19 kHz
> tone gets moved to 0 Hz.

Yep. This turned out to be the problem.
I then replaced it with the "PLL ref out" block which seams to do the trick.



> After that use a Rotator block to shift the spectrum another 38 kHz =
> 57 kHz - 19 kHz

Well, the goal of the exercise is to extract the 57 KHz RDS signal 
purely based on the 19 KHz reference and not be dependent on a signal 
locally generated in gnuradio.
This excludes the use of the rotator block.



Is there a block that is able to 'scale' a signal in the frequency-domain?
I was thinking for something like this:

- calculate the difference in phase of the input signal, as compared 
with the phase of the previous input sample

- create an output-signal with a "n" times phase-difference as compared 
to the previous output sample

That way, using the 19 KHz reference, it would be possible generate both 
the 57 KHz RDS-carrier and the 2375 baud (19KHz /8 ) reference for the 
PSK demodulator


Does something like that exist?


> > Or is there a better way to generate a 57 KHz complex sine-wave from
> > a 19 KHz reference signal?
> There is no need to have a locally generated 57 kHz carrier, when you
> can just use a PLL to phase lock and then a rotator to shift the
> spectrum.

Can you explain this?

As far as I understand it, the rotator moves the frequency up or down 
"n" * ( sample-rate / 2pi), so it is dependent on a 'locally generated' 
reference (the sample-rate inside gnuradio), no?


Or am I wrong?

> -Andy
Cheerio! Kr, Bonne,