Brian, I also think the linear operation would be better, but not so sure if bipolar transistors wouldn't be preferred over MMIC's for this (on bottom part of the spectrum) (ok... is not so handy).
What I can certainly add to the discussion is that power amplification followed by higher rate varactor multiplication is considerably better than a multiple lower multiplication ratios chain. I had that experience on the 411GHz where from a 70MHz(*) xtal osc amplified to several Watt driving varactors and cavities. I jump with few steps to about 45GHz as opposed to a DB6NT like LO chain which was noticeably worst in the close in noise. Using mixers without driving hard the LO or the RF with same marginal level on both ports is possible but you will be in trouble with level settings :-( Not sure how much you would gain there... theoretically something... but then AM to PM conversion is against you so not sure if better or worst. Luis Cupido ct1dmk. (*) x12 x9 x3 x2 w/ 9th harm corner cube harm mixer if my memory serves me well.... [email protected] wrote: > Bruce- > > OK... So, linear operation does therefore seem to be the preferred > way to operate these MMICs rather than operation into compression. > That's what I seem to be observing if only because my final RF > frequency is so high and RX bandwidth so low. > > Having said that, if my frequency synthesis scheme involves a mixer > does the same effect of low frequency noise to phase noise conversion still > take place? After all, the mixer element is typically into compression > if it's a FET based mixer. I assume a diode mixer is more immune to > similar effects? > > I'm trying to grow my intuitive understanding of the subtle sources of > noise. But I don't recall Maas giving much info on this topic in > his otherwise excellent text. > > As always, thanks for your sagely advice. > > -Brian > > > -----Original Message----- > From: [email protected] [mailto:[email protected]]on > Behalf Of Bruce Griffiths > Sent: Monday, December 15, 2008 5:00 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Close-in phase noise question... > > > [email protected] wrote: >> Looking for comment here... >> >> The background: >> I'm working on a sub mm-wave LO chain for >> a ham radio application. While chasing issues >> of close-in phase (ie: within 1KHz of RF >> carrier) by peeling the "layers of the onion", >> I'm starting to question the performance of >> the MMICs that are used as buffers and amps >> following my Wenzel reference OCXOs. >> >> Question(s): >> Should any MMIC be allowed to be driven >> close to compression or into compression >> when striving for best close-in noise? >> >> I know and have seen the NF of a MMIC >> degrade while in compression, but my >> target right now is close-in noise rather >> than broadband noise. >> >> My design, in summary, takes 5MHz up to 630GHz >> via several multipliers and PLL stages. >> >> -Brian >> > Brian > > The increased nonlinearity when driven into compression will enhance the > conversion of low frequency noise to phase noise. > > 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. > > > _______________________________________________ > 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.
