But not necessarily lowest noise Didier
> -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Don Latham > Sent: Sunday, March 08, 2009 8:48 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Reverse isolation > > Best isolation is via a piece of fiber optics. > Don > > Bruce Griffiths > > Lux, James P wrote: > >>> Actually, it depends on the distance from the hot carrier, the > >>> amplitude of the hot carrier and the particular VNA in > question. My > >>> VNA allows me to change filters as well as integration time. > >>> > >> > >> And especially, where is the selectivity in the VNA's > receiver? You > >> might have a 10 Hz filter, but if the receiver's front end is wide > >> open, then the dynamic range requirement might be a challenge to > >> meet. > >> > >> Consider a 30 dB gain amplifier claiming 120dB reverse isolation.. > >> > >> You put in -30dBm and get 0dBm out in the forward direction. > >> Meanwhile, you inject 0dBm into the output of the > amplifier (from the > >> VNA) and you expect to see -120dBm appearing at the input. > Depending > >> on how good the directional coupler/bridge is that feed the port 1 > >> reflected power receiver, you might be facing measuring a -120dBm > >> signal next to a -30dBm signal, which is challenging... > >> > >> Assuming the DUT is linear (hah!) one could just apply load with > >> different reflection coefficients to it when measuring S11. This > >> might even be harder, though... With -120dBm reverse isolation, > >> you're basically looking at seeing the effect of adding a coherent > >> signal 90 dB down to the signal you're already measuring for S11. > >> That's not going to result in a huge change in amplitude or phase > >> (e.g. About 1 part in 1E4 or 1E5).. > >> > >> Maybe for this list, though.. Measuring phase shifts of > 1E-5 radian.. > >> Walk > >> in the park, as it were. > >> > >> Jim > >> > >> > >> _______________________________________________ > >> time-nuts mailing list -- [email protected] To unsubscribe, go to > >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >> and follow the instructions there. > >> > >> > > Jim > > > > Its even more challenging when the isolation amplifier has > a nominal > > gain of 0dB coupled with a reverse isolation of 120dB or more. > > In this case one would be looking at measuring phase shifts on the > > order of 1urad or less. > > > > In this case one could try applying say a +10dBm signal to > the input, > > modulate the load reflection coefficient and look for a modulation > > frequency related sideband at the input port. > > > > Bruce > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > -- > Dr. Don Latham AJ7LL > Six Mile Systems LLP > 17850 Six Mile Road > POB 134 > Huson, MT, 59846 > VOX 406-626-4304 > www.lightningforensics.com > www.sixmilesystems.com > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
