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 Mike Feher wrote: > John - > > I have a nice 3585B, 11729C (with all filters) and a nice working 8662A. I > assume the PN of the 640 output of the 8662A is still more than adequate. > You are suggesting replacing the multiplier within the 11729C with the NLTL > comb generator instead of the currently used SRD. I do not see how the SRD > itself would significantly degrade the source's PN beyond the 20 log N > factor. I will be definitely very interested in your results. 73 - 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 John Miles > Sent: Friday, December 28, 2007 2:42 AM > To: time-nuts@febo.com > Subject: [time-nuts] NLTL comb generators going away... > > FYI, I don't know how many others on the list are interested in microwave PN > measurement with gear like the HP 11729B/C or 70420/E5500 series, but I'm in > the (slow) process of upgrading my own 11729C setup to lower its measurement > floor and thought I'd mention something I learned the other day in case it's > helpful to anyone else. > > Briefly, the HP noise test sets all seem to use low-noise comb generator > modules fed by 600 or 640 MHz from a quiet OCXO-based multiplier chain, with > filters to select the desired comb harmonic to downconvert the signal under > test. Since I'm replacing my 11729C's 10811A-derived 640-MHz source with a > much-quieter ULN OCXO-derived source, I also wanted to upgrade its > step-recovery diode-based comb generator with one of the nonlinear > transmission-line parts produced by Picosecond Pulse Labs. I've been > plotting this upgrade for awhile, but there was no incentive to do it until > upgrading the OCXO. > > NLTL comb geneators are awesome. They have 15-20 dB better residual phase > noise specs than the SRD multipliers that HP was using in the 80s and 90s, > much faster output edges, *and* their inputs are much more broadband in > nature than SRD-multiplier inputs usually are. They work well with input > frequencies over the better part of an octave, whereas the 11729C's > multiplier is very peaky around 640 MHz. All of these attributes make them > ideal for use in high-performance PN downconverters. If you were building a > high-end phase noise test set today, I don't know what else you'd specify. > > Unfortunately, when I called Picosecond Pulse Labs to order my first choice > (the 7103 model), they told me they'd shut down their fab in Oregon and were > no longer producing NLTL multipliers. They have a few left in stock and are > selling them for $975 each regardless of the part number. The connectorized > 7103s were gone when I called, so I bought their last connectorized 7123, > which is one of the higher-spec parts (input=+29 dBm at 800 MHz-1.5 GHz, > output=0 dBm at 50 GHz). It works fine with inputs down to 640 MHz, so > it'll be OK in the 11729C, although it has a 2.4-mm output connector rather > than SMA. > > So this really sucks... hopefully somebody will buy that fab and continue > production, but it sounds like they just didn't sell enough of the comb > generators to be worthwhile. I haven't been able to find any other > off-the-shelf multipliers with additive jitter specs anywhere close. If > this sort of thing is your sort of thing, get 'em while you can. > > Specs: > http://www.picosecond.com/product/category.asp?pd_id=22 > > Residual PN measurement notes: > http://www.picosecond.com/objects/RPN-Measurement.pdf > > -- john, KE5FX > > > _______________________________________________ > 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.