[time-nuts] About HP10544A

Magnus Danielson magnus at rubidium.dyndns.org
Sun Mar 8 16:25:45 UTC 2009

>>> Don't use a high Q bandpass filter as its phase shift tempco will be
>>> relatively high.
>> What do you think if I could find FM radio IF filter somewhere (10.7 
>> MHz) and tune it to 10 MHz? I don't know if there's tunable filters 
>> available anymore because any new ones seems to be ceramic. But maybe 
>> from some old radio could have tunable one (wishful thinking in Finland, 
>> thanks to "recycling" of the electronics).
> Using a 10MHz bandpass filter isn't usually a good idea unless the
> temperature doesn't change too rapidly and the filtered output is phase
> locked to the stable frequency source.
> The phase shift tempco of the bandpass filter then isnt too critical as
> slow changes in the filter phase shift will be corrected by the phase
> lock loop.
> Even so you don't want too high a Q or the filtered signal amplitude
> will change too much over temperature.

You should be able to lower the effective Q value by use of external 
serial or parallel resistor. A parallel resistor will add some 
capacitance, but detuning the frequency should also require some 
additional capacitance so it should work fine in combination.


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