Didier A 10-1000mW of single mode ECDL helps. But then you need a modulator. You would also need to avoid frying any photomixer at the other end.
Bruce Didier wrote: > 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. > > _______________________________________________ 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.
