Re: [time-nuts] NLTL comb generators going away...
Following up an earlier post: 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). ... and it turns out that their conversion efficiency when driven by the 11729C's 640 MHz PA is actually lower than the 7123's was. So, contrary to what I posted earlier, it's necessary to modify the driver for higher power output to use the NLTL multipliers that are still available. The 7103 looks like the best candidate, using a 3-dB pad at the input, but I'm not sure if they have any of those left. -- 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.
Re: [time-nuts] NLTL comb generators going away...
An SRD imposes a phase noise floor that adds to the source's phase noise floor and the multiplier's input noise floor. Whatever this total noise is will be increased by 20 LOG N. Unless the source is very low noise and the multiplier equivalent input noise is very low, you may not see any effects from the SRD. At Agilent we didn't have to worry about SRD noise until exotic sources like the STW were developed. In the case you site, the source noise was 6 dB below the equivalent input noise of the source, resulting in a 1 dB increase in total noise. An SRD may or may not have been worse depending on what the actual noise floor was. Rick Mike Feher wrote: 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.
Re: [time-nuts] NLTL comb generators going away...
The SRD has a wideband noise floor. It probably has some flicker noise, but the source usually dominates that. The SRD stores charge on the forward half of the cycle and then gives back this charge on the reverse half of the cycle. Some charge is lost due to the finite lifetime of the diode, which is a statistical process and may involve some noise. Rick Karlquist N6RK [EMAIL PROTECTED] wrote: My 2 cents At what freq offset are the measurments being made? (NLTL vs. SRD) Is it that the SRD has more flicker noise and thus is worse than 20log(n) for close-in noise? Or does the SRD have a wideband noise floor that is worse than 20log(n)? -Brian, WA1ZMS -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Mike Feher Sent: Saturday, December 29, 2007 9:53 AM To: [EMAIL PROTECTED]; 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] NLTL comb generators going away... 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
Re: [time-nuts] NLTL comb generators going away...
My 2 cents At what freq offset are the measurments being made? (NLTL vs. SRD) Is it that the SRD has more flicker noise and thus is worse than 20log(n) for close-in noise? Or does the SRD have a wideband noise floor that is worse than 20log(n)? Their MWJ reprint talks about that: http://www.picosecond.com/objects/MWJ_reprint.pdf (about 3.5 MB) -- 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.
Re: [time-nuts] NLTL comb generators going away...
Thanks John! I remember seeing the original article in 2006, but did not recall the details. -Brian, WA1ZMS -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of John Miles Sent: Saturday, December 29, 2007 12:16 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] NLTL comb generators going away... My 2 cents At what freq offset are the measurments being made? (NLTL vs. SRD) Is it that the SRD has more flicker noise and thus is worse than 20log(n) for close-in noise? Or does the SRD have a wideband noise floor that is worse than 20log(n)? Their MWJ reprint talks about that: http://www.picosecond.com/objects/MWJ_reprint.pdf (about 3.5 MB) -- 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.
Re: [time-nuts] NLTL comb generators going away...
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.
Re: [time-nuts] NLTL comb generators going away...
John Miles wrote: 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. Not to worry! I'm sure that the Chinese have taken over production, like they have done with the US shoe, textile, appliance, TV, computer, telephone, machine tool, hand tool, yard tool, furniture, food, sports equipment, toy, semiconductor, test equipment... and soon automobile, and airplane industries. I'm learning a new line: Do you want fries with that?... only because of the shifting demographics, I will have to learn to say it in Chinese and Spanish. -Chuck Harris ___ 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.
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 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.
Re: [time-nuts] NLTL comb generators going away...
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. Right; it doesn't make sense to swap out the 11729's SRD multiplier unless you are also upgrading the 640-MHz drive source at the same time. There is some room for improvement in that 640-MHz multiplier chain, though, and the SRD multiplier appears to be the next weak link after the 640-MHz chain is cleaned up. 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 The 8662A's 640 MHz output comes from multiplying a 10811A-class oscillator by 64 (with a 36-dB noise penalty) and shaving off the noise sidebands with a couple of monolithic crystal filters. At 1 kHz from the carrier, the PN spec from the 640-MHz output is -121 dBc/Hz; at 10 kHz it's -145 dBc/Hz. So, say you're measuring a 10 GHz carrier with your 11729C. You use the 15th harmonic of 640 MHz for that (24 dB penalty). Your measurement floor at 9600 MHz is -97 dBc/Hz (1 kHz) to -121 dBc/Hz (10 kHz). These levels are comfortably above the 11729C's residual noise spec at 10 GHz (-132 dBc/Hz quoted on page 42 of AN 11729B-1). However, the target specs for my upgraded 8662A reference chain's 640 MHz output are circa -142 dBc/Hz (1 kHz) to 158 dBc/Hz (10 kHz). At 9600 MHz this would be -118 dBc/Hz to -134 dBc/Hz. My thinking is that the NLTL multiplier adds some headroom insurance at that point. According to Picosecond, the NLTL floor is at or below the thermal limit of their test setup (-140 dBc/Hz or better). Their marketing spiel is centered around the idea that their multiplier will not degrade the PN of the quietest crystal oscillators available. That's not true of SRDs, in my understanding. An exercise in lily-gilding, certainly, but that seems to be the point around here. :) -- 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.
Re: [time-nuts] NLTL comb generators going away...
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.
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.
