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Re: creating a 57 KHz signal from 19 KHz reference
From: |
Andy Walls |
Subject: |
Re: creating a 57 KHz signal from 19 KHz reference |
Date: |
Fri, 15 Nov 2019 12:16:09 -0500 |
User-agent: |
Evolution 3.32.2 (3.32.2-1.fc30) |
> 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