[time-nuts] ? phase comparison or other device

Magnus Danielson magnus at rubidium.dyndns.org
Mon Jun 25 04:50:14 EDT 2007

From: Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] ? phase comparison or other device
Date: Mon, 25 Jun 2007 20:37:29 +1200
Message-ID: <467F7EC9.8090602 at xtra.co.nz>

> Ulrich Bangert wrote:
> > Pete,
> >
> >   
> >>>>  5. Mini-circuits BLP-1.9 low pass filter.
> >>>>         
> >
> > terminating the mixer if output with an lowpass/bandpass filter and NOT
> > with an diplexer is not so good an idea. Where does the rf go?
> >
> > Best regards
> > Ulrich Bangert
> >
> >   
> Ulrich
> This depends on whether the low pass filter has a shunt capacitor at its 
> input or a series inductor.
> With the shunt capacitor the RF is shunted to ground through this capacitor.
> With a series inductor the RF sees a relatively high input impedance and 
> the mixer will not perform well.

Depends on what you want to acheive. NIST made some experiments and found that
this was indeed what increased the gain in the frequency comparisions they
made. They where infact a bit supprised as this was contruary to what they
beleived. It's in the NIST archive, but I could pull the document number out if
given some chance to dig around.

So, what is normally a good thing in RF may not necessarilly be the best
strategy for frequency comparision, at least when it comes to mixers.


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