Over 20 years ago I was the lead guy in the development of the SCOTT Milstar satellite terminal at Magnavox. Our uplink frequency was from 43.5 to 45.5 GHz. The PN specifications were essentially almost impossible to meet. The terminal had it's own specification and used a Rubidium followed by a 100 Hz crystal filter. Narrow filtering was used after all multipliers and a lot of heterodyning was used in place of multipliers to come up with the 11 GHz required for the PA. The PA was subcontracted out to two different manufacturers due to the risks involved and they were each given 1 dB above what would have been generated within the PA's X4 multiplier in PN increase. So, instead of 12 dB they were allowed 13 dB of degradation. The multiplier used was a dual stage varactor type multiplier, where the first stage would get it up to 22 GHz and the second to the final frequency of the nominal 44 GHz. None of the amplifiers exhibited more than 12 dB of PN increase. In fact, they all measured 12 dB. Admittedly, back then, this was not an easy measurement to make. This was with 2 different manufacturers and I went to both on numerous occasions, one on the east coast and one on the west. So, this is why I wonder why an SRD would be that much worse. What is happening that I am not aware of? Where is this extra residual noise coming from? Thanks - Mike
Mike B. Feher, N4FS 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Rick Karlquist Sent: Friday, December 28, 2007 9:00 PM To: Discussion of precise time and frequency measurement Cc: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] NLTL comb generators going away... You need a really clean driver to be good enough to need a NLTL instead of an SRD. Whatever the intrinsic noise of the NLTL is, it is lower than any practical source so you can consider it zero. Rick Karlquist N6RK John Miles wrote: > It's hard to read the tea leaves on that. Dieter Scherer has one note > (Generation of Low PN Microwave Signals) that shows the 33004A > multiplier's > output noise at -140 dBc/Hz to -148 dBc/Hz from 1 to 10 kHz, at 5.5 GHz > (N=11). If that is the case with the 11729's multiplier, then the NLTL > part > is not really necessary even with an upgraded 640 MHz reference chain. > But > then, something else must be responsible for the 11729's residual PN spec, > and I don't see what that would be. > > Of course, I'd assume that PSPL's measurements were taken with the > crappiest > SRD part they could find. :) > > It appears that the 11729's 640-MHz PA can drive the 7123 adequately, > although the 12.16 GHz comb line is somewhat close to the spec limit of > -20 > dBm. The 7113-110 is a better replacement for the 33004A in the 11729C, > since it would actually be operating in spec. They have several of those > in > stock (I just ordered 2 of the 8 they had left). > > -- john, KE5FX > >> -----Original Message----- >> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] >> Behalf Of Richard (Rick) Karlquist >> Sent: Friday, December 28, 2007 10:08 AM >> To: Discussion of precise time and frequency measurement >> Subject: Re: [time-nuts] NLTL comb generators going away... >> >> >> The SRD (step recovery diode) definitely degrades the phase >> noise beyond 20 LOG N, according to Agilent engineers I have >> talked to. They mentioned a number like -150 dBc/Hz or something. >> Having said that, you also have to be very careful to design >> the driver (especially with NLTL) or it will become the limiting >> factor. >> >> Rick Karlquist N6RK >> > > > _______________________________________________ > 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. _______________________________________________ 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.