[time-nuts] Photodiodes for high frequency OPLL
Attila Kinali
attila at kinali.ch
Mon Apr 1 12:52:26 EDT 2013
On Mon, 1 Apr 2013 14:24:58 +0100
Wolfgang <timenuts at triplespark.net> wrote:
> On Monday 01 April 2013, Attila Kinali wrote:
> >> [APD...]
> >
> > I think the gain modulated approach to downconvert the signal should work.
> >
> Anyway, each of these down-mixing approaches needs to resolve the
> mirror frequency problem. I.e. if you modulate your receiver with
> 7.1 GHz (or use an EOM to do that optically) and detect at 100 MHz,
> you do not know whether the input signal has an offset of 7.2 GHz
> or 7.0 GHz.
> So you might be locking on the wrong one.
If i'm not mistaken, this shouldn't be a problem
I'm not demodulating the laser, but using a PLL to fix the difference
frequency. Being on the wrong side would invert the sign on the loop
gain, thus the mirror freuquency would be an unstable point.
Attila Kinali
--
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