[time-nuts] Advice on 10 MHz isolation/distribution (Clay)

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Feb 18 23:23:43 UTC 2010

Hal Murray wrote:
>> The problem is modulation of the reference signal via relative
>> movement of the transformer guts.  While I understand there are ways
>> to 'harden' magnetic devices, my application is far too sensitive to
>> even consider a magnetic approach given the availability of
>> alternatives.  Any spurious signals present on the 10 MHz reference
>> will be increased by 56 dB by the phase-locked loop.
> Capacitors are piezoelectric too.
> Does anybodyhave any handy numbers for this sort of stuff?
Most high K ceramic caps are ferroelectric below the Curie temperature 
and paraelectic above that.
The resultant capacitance nonlinearity can allow low frequency noise to 
phase modulate a capacitor coupled RF signal if the phase shift due to 
the capacitor is sufficiently large.
Yet another reason to avoid high K ceramic capacitors or at least ensure 
that the RF phase shift due to such capacitors is sufficiently small.

Low frequency magnetic fields can phase modulate transformer coupled RF 
signals by modulating the transformer phase shift.


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