Re: creating a 57 KHz signal from 19 KHz reference

[Andy Walls]

> 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.

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

Then use an FIR/FFT filter block with low pass taps to isolate your RDS
signal. 

> 
> Itried using a PLL carrier-tracking block to extract the 19 KHz
> carrier (which seams to work) and direct that carrier to a 3 input
> multiplier block, but that does not seams to work. Even after
> filtering out DC and the carrier at  -19 KHz (negative frequency),
> the output of the multiplier is always zero. (*)

You have neglected that that PLL block performs a spectrum shift as
well as tracking the pilot signal.  Put a QT GUI Freq sink on the
output of the PLL carrier tracking block to see.
> 
> 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.

-Andy