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.