[time-nuts] NLTL comb generators going away...

[Richard (Rick) Karlquist]

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: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of John Miles
> Sent: Friday, December 28, 2007 2:42 AM
> To: time-nuts at 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 at 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 at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> 
>