Hi Implementing that circuit without using a hybrid would be a bit of a challenge.
Bob On Feb 10, 2010, at 11:30 PM, Bruce Griffiths wrote: > Clay > > Circuit schematic for a more recent JPL isolation amplifier design is > attached. > > Bruce > > life speed wrote: >> Avoiding transformers and inductors will make it virtually impossible to >> achieve very low phase noise as the dc gain from say the base of any >> transistor in the chain to the output will degrade the flicker phase >> noise. Using transformers or using an inductor to shunt any collector >> resistors reduces the flicker phase modulation to low levels. >> >> JPL in the past has built capacitively coupled complementary symmetry >> isolation amplifiers that avoid transformers but suffer from dc loop >> gains of around 3 or so. >> >> Using complementary symmetry can be a good way of keeping the dc current >> down. >> >> How much reverse isolation do you need? >> How low does the phase noise floor need to be? >> What about flicker phase noise, how low does that need to be? >> >> Bruce >> >> Right, what do I really need? I only have a really good 10 MHz OCXO crystal >> oscillator to distribute, so about -120 dBc at 10 Hz, -140 dBc/Hz at 100 Hz, >> - 150 dBc/Hz at 1KHz, and -155 dBc/Hz noise floor. No maser or cesium >> clock, living in the world of practical realities here. Of course I would >> like to be 3 - 6 dB better than the OCXO numbers. >> >> Reverse isolation is my primary interest in the distribution amplifier >> approach, although the OCXO is good enough that a sloppy approach could >> contaminate the phase noise also. I would like to accomplish at least 100 >> dB reverse isolation at frequencies below 20 MHz, but more is better in this >> case. The 10 MHz is running all over a noisy aircraft, to potentially noisy >> receivers. >> >> In reading up on the subject, I have come to understand that DC gain is the >> bane of close-in phase noise. Given that flicker noise is such a headache >> for we frequency synthesizer designers, I guess this should come as no >> surprise. >> >> Clay (AKA Lifespeed) >> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > <JPL_Iso_Amp_2A.png>_______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.