Re: [time-nuts] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
On 10/02/2014 09:21 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: On 2 Oct 2014 07:10, Magnus Danielson mag...@rubidium.dyndns.org wrote: David, The character of starting high/low and then stabilize some 5-30 min later is typical of oven oscillators. Underdamped ovens have been seen before, I have even seen one on the brink of oscillation. Thank you. Do you know the likely cause of the somewhat odd behaviour between about 150 and 220 s? Could be that it overshoots in this non-linear way due to a little low cooling, so that as the heater runs full current, it doesn't cool of quick enough for the transition to be nice and linear. Rather it overshoots, turn heater off and then cools off and the heater smoothly goes on again and stabilizes. It's not a big problem. You can have too little cooling, and then the heater chirps the heater and then the crystal decays in temperature to get a heater chirp again. This is really bad and leaves the crystal unstabilized for most of the time and you get a modulation on frequency from the saw-tooth temperature. You don't look to be close to that, but I've seen it happen. This eBay auction, which someone posted http://m.ebay.com/itm/151256172424 says it's the high stability oscillator for an HP 8753D or 8753ES. I checked the part number at parts.keysight.comand it would appear it is the same as used in my VNA and several other microwave VNAs. That said, I have noticed a few errors on parts.agilent.com, one of which resulted in me buying the wrong part. I was later warned by Agilent not to trust the accuracy too much, especially on older equipment. It is better to check with them before making purchases. But they have a very helpful parts service that does make every effort to sort out what parts are. They spent quite some time finding out what connectors were on am obsolete cable for me. TCXO will not have the same wide range, as it compensate for the temperature. This answers my original curiosity now - did I have an OCXO or TCXO. With that curve it is definitely an OCXO, and my guess is that it is an SC-cut, which matches starting +40 ppm high (if I recall things correctly). It is also typical for 2 OCXO oscillators and the expected Q and thus noise will come at handy in a VNA. Although I am not going to bother, as it will be easier and more accurate to feed the VNA from a rubidium or GPS locked TCXO/OCXO, it would probably be possible to buy one of those off of eBay and replace the OCXO with a better one. Then stick it in my VNA - I would not want to modify the original one. There have some rather small double oven OCXOs on eBay recently for very little money. From the earlier comments about this oscillator, it would appear its specification is quite poor for an OCXO. On time-nuts, things can get a little exaggerated in the poor aspect. What is more relevant is will it greatly affect your VNA performance? Precision on frequency is trimmable once the oven has been well heated. Noise-wise I would say it suffice. What is your VNA frequency resolution anyway? 1 Hz? Cheers, Magnus ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
Tim, The shape does not look exactly what I would expect from a less than critical damped oven, it looks a little to peaky, but maybe it is the resolution of the graph that fools my eye. Agree that you end up in critical damped oven with fast warmup requirement. Cheers, Magnus On 10/02/2014 02:41 PM, Tim Shoppa wrote: The overshoot behavior from 150 to 220 seconds is exactly what you expect for slightly less than critical damping which is where many closed loops end up when rapid lock or warmup is a criteria. Most rapid warmup is almost always the design point of an OCXO oven. Tim N3QE On Thu, Oct 2, 2014 at 3:21 AM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: On 2 Oct 2014 07:10, Magnus Danielson mag...@rubidium.dyndns.org wrote: David, The character of starting high/low and then stabilize some 5-30 min later is typical of oven oscillators. Underdamped ovens have been seen before, I have even seen one on the brink of oscillation. Thank you. Do you know the likely cause of the somewhat odd behaviour between about 150 and 220 s? This eBay auction, which someone posted http://m.ebay.com/itm/151256172424 says it's the high stability oscillator for an HP 8753D or 8753ES. I checked the part number at parts.keysight.comand it would appear it is the same as used in my VNA and several other microwave VNAs. That said, I have noticed a few errors on parts.agilent.com, one of which resulted in me buying the wrong part. I was later warned by Agilent not to trust the accuracy too much, especially on older equipment. It is better to check with them before making purchases. But they have a very helpful parts service that does make every effort to sort out what parts are. They spent quite some time finding out what connectors were on am obsolete cable for me. TCXO will not have the same wide range, as it compensate for the temperature. This answers my original curiosity now - did I have an OCXO or TCXO. Although I am not going to bother, as it will be easier and more accurate to feed the VNA from a rubidium or GPS locked TCXO/OCXO, it would probably be possible to buy one of those off of eBay and replace the OCXO with a better one. Then stick it in my VNA - I would not want to modify the original one. There have some rather small double oven OCXOs on eBay recently for very little money. From the earlier comments about this oscillator, it would appear its specification is quite poor for an OCXO. Cheers, Magnus Thank you. Dave ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
On 4 October 2014 07:57, Magnus Danielson mag...@rubidium.dyndns.org wrote: This answers my original curiosity now - did I have an OCXO or TCXO. With that curve it is definitely an OCXO, and my guess is that it is an SC-cut, which matches starting +40 ppm high (if I recall things correctly). It is also typical for 2 OCXO oscillators and the expected Q and thus noise will come at handy in a VNA. Although I am not going to bother, as it will be easier and more accurate to feed the VNA from a rubidium or GPS locked TCXO/OCXO, it would probably be possible to buy one of those off of eBay and replace the OCXO with a better one. Then stick it in my VNA - I would not want to modify the original one. There have some rather small double oven OCXOs on eBay recently for very little money. From the earlier comments about this oscillator, it would appear its specification is quite poor for an OCXO. On time-nuts, things can get a little exaggerated in the poor aspect. I would never have guessed that What is more relevant is will it greatly affect your VNA performance? No, not at all. About the only application I can think of where very high frequency accuracy would be needed would be to look at crystals. And for that, this analyzer, covering 50 MHz to 20 GHz is not likely to be the ideal too. I have just in fact bought one which covers 300 kHz to 9 GHz. Precision on frequency is trimmable once the oven has been well heated. Noise-wise I would say it suffice. I don't think there's much point me trimming it, even if I cesium here. I think it is good enough for my application. I have a couple of rubidium oscillators here, and bought them to make a lab standard, but then I wondered whether the phase noise might have been worst than what I already have, and that was likely to be more important to me than absolute frequency accuracy. What is your VNA frequency resolution anyway? 1 Hz? Yes, 1 Hz. HP took the a bit with the earlier models of the 8720 series. The 8720A, 8720B and I think the 8720C too, all had a default resolution of 100 kHz !!! To get one Hz, you needed a software upgrade - enter a keyword. I would have found 100 kHz too limiting, but what I have is good enough. Cheers, Magnus Dave ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
Dave, Thanks for the raw data. Attached is my plot. Your data looks ok to me. If you're interested here are some random comments about your 8720D-1D5-oscillator-frequency.csv file: - Thanks for including the description of the data as comments in the file. I can't tell you how many times I get data files from people and you have to play 20 questions before you know what the columns are, or what the units are, or what the sampling interval is, etc. - Thanks for including the elapsed time (column 6) as part of the data set. This is the preferred way to determine the sampling interval; 6.3 seconds in this case. - You can see the finite resolution of the counter. For example, looking at these five lines: 10.2500 10.1300 10. 9.8800 9.8100 we can see it's a 7 digit measurement. Notice the last two digits are always 00. For a warm-up test, where the oscillator is changing by tens of ppm over several minutes, 7 digits is sufficient. So no worries there. - You have 355 data points. Notice that the last 319 measurements are all 9.9400. This is partly due to the fact that the OCXO has warmed up by this point. But this is mostly due to the fact that your OCXO is now more stable than the counter has resolution. - Out of habit my plot uses ppm units rather than Hz. I converted your frequency measurements to relative frequency error. For example, a frequency of 10.00013100 MHz the error is (10.00013100 - 10) / 10 or 1.31e-5. The five frequency lines above simply become: 2.5e-6 1.3e-6 0.0 -1.2e-6 -1.9e-6 and this shows that even though it's a 7 digit counter there are only 2 or 3 digits of resolution (the DUT being quite close to 10 MHz). - By the time you get to all the 9.9400 MHz readings, the counter is down to 1 digit of resolution, e.g., -6e-7. - Most people plot points and draw interpolated lines between them. The Stable32 plot I attached shows a staircase. This is partly due to the fact that the raw data is quantized in both the x and y axis (sample quantization is 6.3 s, frequency quantization is 1 Hz). It is partly done to convey that frequency is inherently an average across some interval rather than a point measurement. Again, none of this has any impact on your original question about your VNA timebase, but I thought you might be interested in what's hidden in the data. Now imagine the fun you could have making 12 digit measurements... /tvb - Original Message - From: Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Saturday, October 04, 2014 3:38 AM Subject: Re: [time-nuts] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on On 4 October 2014 08:01, Magnus Danielson mag...@rubidium.dyndns.org wrote: Tim, The shape does not look exactly what I would expect from a less than critical damped oven, it looks a little to peaky, but maybe it is the resolution of the graph that fools my eye. I stuck the raw data as an attachment, so that should not fool your eye. It is only a few kB as compressed, and not that big when uncompressed. But be careful in trying to do too much with the data after it has settled down, as I have no idea of the accuracy or stability of the time base in the HP 70310A precision frequency reference which is used to measure the VNA. I have no idea when it was calibrated. But it had been powered on at least 24 hours. I don't even know the specification of that - it might be better or worst than the VNAs oven, but at least the VNA has been regularly calibrated. What is a bit odd is one of the tests of the VNA performed by Agilent/Keysight is the frequency accuracy at 20 GHz. Although when calibrated by Agilent a year ago there was some error, this time it was spot on 20. .. GHz. But when the 10 MHz oscillator was measured, there was some error. Of course, there will be some errors in the VCO / PLL and the timebase could have drifted between the two measurements, so such differences are not entirely unexpected. The 3 cal certificates I have for this are here, in order of date (most recent first) 1) Keysight a few weeks ago http://www.kirkbymicrowave.co.uk/cal_certificates/Keysight-standard-calibration-with-uncertainties-for-8720D-vector-network-analyzer-16-09-2014.pdf 2) Agilent just over a year ago http://www.kirkbymicrowave.co.uk/cal_certificates/Agilent-standard-calibration-with-uncertainties-for-8720D-vector-network-analyzer.pdf 3) Techmaster (lacks any useful information), about 2 years ago http://www.kirkbymicrowave.co.uk/cal_certificates/Techmaster-8720D-vector-network-analyzer-cal-certificate-EXPIRED.png Although the Techmaster one tells you nothing useful, the Agilent and Keysight ones do give frequency information, including the uncertainty, which has actually increased since it was calibrated
Re: [time-nuts] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
On 4 October 2014 13:24, Tom Van Baak t...@leapsecond.com wrote: Dave, Hi Tom Thanks for the raw data. Attached is my plot. Your data looks ok to me. Great If you're interested here are some random comments about your 8720D-1D5-oscillator-frequency.csv file: Sure - Thanks for including the description of the data as comments in the file. I can't tell you how many times I get data files from people and you have to play 20 questions before you know what the columns are, or what the units are, or what the sampling interval is, etc. Yes, I can imagine it. Some people have some odd ways of presenting data. Slightly different, but I recall trying to help a student debug her software. It became apparent that all variable names were Disney characters! The number of photons might have Aladdin, the absorption coefficient MickyMouse, the scattering coefficient SnowWhite ... I believe she went onto work with missiles, which is worrying. - Thanks for including the elapsed time (column 6) as part of the data set. This is the preferred way to determine the sampling interval; 6.3 seconds in this case. It seems the obvious one to me. - You have 355 data points. Notice that the last 319 measurements are all 9.9400. This is partly due to the fact that the OCXO has warmed up by this point. But this is mostly due to the fact that your OCXO is now more stable than the counter has resolution. Yes, I see that. - Out of habit my plot uses ppm units rather than Hz. I converted your frequency measurements to relative frequency error. For example, a frequency of 10.00013100 MHz the error is (10.00013100 - 10) / 10 or 1.31e-5. The five frequency lines above simply become: 2.5e-6 1.3e-6 0.0 -1.2e-6 -1.9e-6 Yes, I can see the logic of that. At least to a time-nut. Not so sure I would present it like that to most people. and this shows that even though it's a 7 digit counter there are only 2 or 3 digits of resolution (the DUT being quite close to 10 MHz). I should have a look to see if that can be improved. I hacked the the software to collect that together in 15 minutes or so, but it was heavily based on something I wrote in 2008. At that time, the job was urgent and on some occasoins I was working to 2 AM to get the code finished. I doubt it well written as it could be. Perhaps the resolution could be improved. I guess I should also get a better counter. I used to have a HP 5370B, but sold it to someone on this list - a decision I later regretted. I have thought of buying another microwave counter (mine is pretty dead), but I doubt that would have the resolution of a lower frequency model. And microwave counters tend to be quite expensive. - By the time you get to all the 9.9400 MHz readings, the counter is down to 1 digit of resolution, e.g., -6e-7. Yes. - Most people plot points and draw interpolated lines between them. The Stable32 plot I attached shows a staircase. This is partly due to the fact that the raw data is quantized in both the x and y axis (sample quantization is 6.3 s, frequency quantization is 1 Hz). It is partly done to convey that frequency is inherently an average across some interval rather than a point measurement. I see Stable32 is some specialist software for time-nut related items. Again, none of this has any impact on your original question about your VNA timebase, but I thought you might be interested in what's hidden in the data. Now imagine the fun you could have making 12 digit measurements... I guess I will have to look for another 5370B! If I recall correctly, when I did look some time ago at getting another TI counter, the Agilent 53230A seemed to have some specifications *worst* than the 5370B it replaced. It was not clear it was an upgrade. This 53230A on eBay does not seem very good value, at about 60% *more* than the price of a new one from Keysight!!! http://www.ebay.co.uk/itm/COUNTER-TIMER-350MHZ-12-Digits-20PS-53230A-/ Perhaps I should ask what discount I could get if I buy 10! I just stuck an offer on a SRS 620, which is sold as seen. I'll take a chance it works if my offer is accepted. Dave ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
-Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Dr. David Kirkby (Kirkby Microwave Ltd) ... If I recall correctly, when I did look some time ago at getting another TI counter, the Agilent 53230A seemed to have some specifications *worst* than the 5370B it replaced. It was not clear it was an upgrade. This 53230A on eBay does not seem very good value, at about 60% *more* than the price of a new one from Keysight!!! http://www.ebay.co.uk/itm/COUNTER-TIMER-350MHZ-12-Digits-20PS-53230A-/ Perhaps I should ask what discount I could get if I buy 10! I just stuck an offer on a SRS 620, which is sold as seen. I'll take a chance it works if my offer is accepted. The 5370B is still the only high-performance counter that I own, personally. SR620s are fine as far as they go, but if they have any strong advantages over the 5370 I don't know what they are. Spending more for a 53230A isn't necessary unless you have a specific need for something that only it can do (and I don't). One cool thing about the 5370 is that the newest TimeLab beta has JavaScript support for it. Previous versions supported scripting only for TimePods. It comes with an example script to record frequency readings at one per second for 7 days, after waiting 5 minutes for initial oven warmup. My OCXO test bench runs on a 5370B in a separate building. I go over there once a week, swap the oscillator under test, restart the script, and forget about it until the next week. (E.g.,: http://www.ke5fx.com/ocxotest.png , generated by the TimeLab version at http://www.miles.io/timelab/beta.htm). It's pretty handy for just this sort of scenario. -- john, KE5FX Miles Design LLC ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
On 4 October 2014 23:03, John Miles j...@miles.io wrote: I just stuck an offer on a SRS 620, which is sold as seen. I'll take a chance it works if my offer is accepted. The 5370B is still the only high-performance counter that I own, personally. SR620s are fine as far as they go, Is it me, or do they look very cheaply made? I have never seen one for real, but the photo I see on eBay looked more like a $200 Chinese power scope. I used an Standard Research SR-830 lock-in amplifier extensively during my Ph.D. It was really nice to use. But the SRS 620 looked rather cheap to me. but if they have any strong advantages over the 5370 I don't know what they are. Spending more for a 53230A isn't necessary unless you have a specific need for something that only it can do (and I don't). I never really looked into it. I just made a low offer on an SRS 620 on eBay. I am annoyed with myself for selling the 5370B. I don't really have any immediate need for another TI counter - what need I did have, has since gone. But if I could get one cheap enough, I would. Dave ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
Out of curiosity, what's the difference between the two first traces? One looks more jump than the other. Cheers, Magnus On 10/05/2014 12:03 AM, John Miles wrote: -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Dr. David Kirkby (Kirkby Microwave Ltd) ... If I recall correctly, when I did look some time ago at getting another TI counter, the Agilent 53230A seemed to have some specifications *worst* than the 5370B it replaced. It was not clear it was an upgrade. This 53230A on eBay does not seem very good value, at about 60% *more* than the price of a new one from Keysight!!! http://www.ebay.co.uk/itm/COUNTER-TIMER-350MHZ-12-Digits-20PS-53230A-/ Perhaps I should ask what discount I could get if I buy 10! I just stuck an offer on a SRS 620, which is sold as seen. I'll take a chance it works if my offer is accepted. The 5370B is still the only high-performance counter that I own, personally. SR620s are fine as far as they go, but if they have any strong advantages over the 5370 I don't know what they are. Spending more for a 53230A isn't necessary unless you have a specific need for something that only it can do (and I don't). One cool thing about the 5370 is that the newest TimeLab beta has JavaScript support for it. Previous versions supported scripting only for TimePods. It comes with an example script to record frequency readings at one per second for 7 days, after waiting 5 minutes for initial oven warmup. My OCXO test bench runs on a 5370B in a separate building. I go over there once a week, swap the oscillator under test, restart the script, and forget about it until the next week. (E.g.,: http://www.ke5fx.com/ocxotest.png , generated by the TimeLab version at http://www.miles.io/timelab/beta.htm). It's pretty handy for just this sort of scenario. -- john, KE5FX Miles Design LLC ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
Dave, On 10/05/2014 12:13 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: On 4 October 2014 23:03, John Miles j...@miles.io wrote: I just stuck an offer on a SRS 620, which is sold as seen. I'll take a chance it works if my offer is accepted. The 5370B is still the only high-performance counter that I own, personally. SR620s are fine as far as they go, Is it me, or do they look very cheaply made? I have never seen one for real, but the photo I see on eBay looked more like a $200 Chinese power scope. I used an Standard Research SR-830 lock-in amplifier extensively during my Ph.D. It was really nice to use. But the SRS 620 looked rather cheap to me. Don't judge it on looks alone. While I would have made a few design aspects differently, I think it's a rather nice unit and it does perform better than the 5370B. but if they have any strong advantages over the 5370 I don't know what they are. Spending more for a 53230A isn't necessary unless you have a specific need for something that only it can do (and I don't). I never really looked into it. I just made a low offer on an SRS 620 on eBay. I am annoyed with myself for selling the 5370B. I don't really have any immediate need for another TI counter - what need I did have, has since gone. But if I could get one cheap enough, I would. If you find a SR620 for a good price, then it's definitly a good thing to have. Cheers, Magnus ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
Hi Both the 5370 and the 620 are getting a bit old. They both run (relatively) hot. Each has their own reliability issues. The 5370 was the more common of the two. Finding parts for it will be easier long term than a 620. Keeping either one fully up to spec long term is likely to be a bit involved. Best bet - get more than one of which ever one you pick. Bob On Oct 4, 2014, at 6:35 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Dave, On 10/05/2014 12:13 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: On 4 October 2014 23:03, John Miles j...@miles.io wrote: I just stuck an offer on a SRS 620, which is sold as seen. I'll take a chance it works if my offer is accepted. The 5370B is still the only high-performance counter that I own, personally. SR620s are fine as far as they go, Is it me, or do they look very cheaply made? I have never seen one for real, but the photo I see on eBay looked more like a $200 Chinese power scope. I used an Standard Research SR-830 lock-in amplifier extensively during my Ph.D. It was really nice to use. But the SRS 620 looked rather cheap to me. Don't judge it on looks alone. While I would have made a few design aspects differently, I think it's a rather nice unit and it does perform better than the 5370B. but if they have any strong advantages over the 5370 I don't know what they are. Spending more for a 53230A isn't necessary unless you have a specific need for something that only it can do (and I don't). I never really looked into it. I just made a low offer on an SRS 620 on eBay. I am annoyed with myself for selling the 5370B. I don't really have any immediate need for another TI counter - what need I did have, has since gone. But if I could get one cheap enough, I would. If you find a SR620 for a good price, then it's definitly a good thing to have. Cheers, Magnus ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
Out of curiosity, what's the difference between the two first traces? One looks more jump than the other. These are all factory new OCXOs (in this case, they're TimePod spare parts undergoing incoming test before I put them on the shelf). The 1303-series parts both exhibited a small jump at around 18 hours, which I thought was interesting, and the blue trace is a bit cleaner, but they're all within spec. The first two are from a lot that's more than 18 months older than the green one being tested now. I have a few more of the new ones to test, at which point I'll have a better feel for how they compare to the older ones. Is it me, or do they look very cheaply made? I have never seen one for real, but the photo I see on eBay looked more like a $200 Chinese power scope. In real life the SR620s aren't badly built, and they're excellent performers, but I don't know of any aspects other than frequency input range in which they outperform a 5370. (What specs are you referring to, Magnus?) You can get them with an optional built-in rubidium standard, so those will have better stability and accuracy numbers than a 5370. But you're better off without that particular option, because it has a stupidly-loud fan that runs as long as the counter is plugged in. With the 5370 you get the classic HP front panel look and feel, but actually the front panel slide switches are one of the biggest problems with 5370s. They're poorly shielded from the elements and rather fragile in operation. Bob's right when he recommends owning a second unit for backup service and/or parts donation. Arguably that's not as important with an SR620, since they're newer and have a good reputation for reliability. -- john, KE5FX Miles Design LLC ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
Hi I’m not sure *what* goes wrong with the SR-620’s. I do know that I have a couple of them that have problems. Maybe I’m just very good at killing test gear …. One day I’ll sit down and dig through the pile. Bob On Oct 4, 2014, at 8:39 PM, John Miles j...@miles.io wrote: Out of curiosity, what's the difference between the two first traces? One looks more jump than the other. These are all factory new OCXOs (in this case, they're TimePod spare parts undergoing incoming test before I put them on the shelf). The 1303-series parts both exhibited a small jump at around 18 hours, which I thought was interesting, and the blue trace is a bit cleaner, but they're all within spec. The first two are from a lot that's more than 18 months older than the green one being tested now. I have a few more of the new ones to test, at which point I'll have a better feel for how they compare to the older ones. Is it me, or do they look very cheaply made? I have never seen one for real, but the photo I see on eBay looked more like a $200 Chinese power scope. In real life the SR620s aren't badly built, and they're excellent performers, but I don't know of any aspects other than frequency input range in which they outperform a 5370. (What specs are you referring to, Magnus?) You can get them with an optional built-in rubidium standard, so those will have better stability and accuracy numbers than a 5370. But you're better off without that particular option, because it has a stupidly-loud fan that runs as long as the counter is plugged in. With the 5370 you get the classic HP front panel look and feel, but actually the front panel slide switches are one of the biggest problems with 5370s. They're poorly shielded from the elements and rather fragile in operation. Bob's right when he recommends owning a second unit for backup service and/or parts donation. Arguably that's not as important with an SR620, since they're newer and have a good reputation for reliability. -- john, KE5FX Miles Design LLC ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
David, The character of starting high/low and then stabilize some 5-30 min later is typical of oven oscillators. Underdamped ovens have been seen before, I have even seen one on the brink of oscillation. TCXO will not have the same wide range, as it compensate for the temperature. Cheers, Magnus On 10/01/2014 10:11 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: Further to my question the other day about what type of oscillator was used in the HP 8720D VNA, fitted with the high stability oscillator option (1D5), here is the frequency as the instrument is switched on, after being powered off for 2-3 hours. The oscillator appears to start too high in frequency, overshoots downwards, then settles down. It would be a somewhat useless exercise collecting data for much loonger and looking at in detail, since I don't know the accuracy of the HP spectrum analyzer. But that had been on for at least 24 hours. The measurement system was an HP 7 system spectrum analyzer, fitted with the 70310A precision frequency reference. This has not been calibrated in years. I will get one of those Jackson labs GPS frequency references, then I will know what the frequency is!! Assuming the crystal frequency is only a function of temperature, (and I know that not to be the case), it looks as if the oven is under damped to me. Is this behavior typical of a TCXO, OCXO or whatever ?? Any comments??? Dave ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
On 2 Oct 2014 07:10, Magnus Danielson mag...@rubidium.dyndns.org wrote: David, The character of starting high/low and then stabilize some 5-30 min later is typical of oven oscillators. Underdamped ovens have been seen before, I have even seen one on the brink of oscillation. Thank you. Do you know the likely cause of the somewhat odd behaviour between about 150 and 220 s? This eBay auction, which someone posted http://m.ebay.com/itm/151256172424 says it's the high stability oscillator for an HP 8753D or 8753ES. I checked the part number at parts.keysight.comand it would appear it is the same as used in my VNA and several other microwave VNAs. That said, I have noticed a few errors on parts.agilent.com, one of which resulted in me buying the wrong part. I was later warned by Agilent not to trust the accuracy too much, especially on older equipment. It is better to check with them before making purchases. But they have a very helpful parts service that does make every effort to sort out what parts are. They spent quite some time finding out what connectors were on am obsolete cable for me. TCXO will not have the same wide range, as it compensate for the temperature. This answers my original curiosity now - did I have an OCXO or TCXO. Although I am not going to bother, as it will be easier and more accurate to feed the VNA from a rubidium or GPS locked TCXO/OCXO, it would probably be possible to buy one of those off of eBay and replace the OCXO with a better one. Then stick it in my VNA - I would not want to modify the original one. There have some rather small double oven OCXOs on eBay recently for very little money. From the earlier comments about this oscillator, it would appear its specification is quite poor for an OCXO. Cheers, Magnus Thank you. Dave ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
The overshoot behavior from 150 to 220 seconds is exactly what you expect for slightly less than critical damping which is where many closed loops end up when rapid lock or warmup is a criteria. Most rapid warmup is almost always the design point of an OCXO oven. Tim N3QE On Thu, Oct 2, 2014 at 3:21 AM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: On 2 Oct 2014 07:10, Magnus Danielson mag...@rubidium.dyndns.org wrote: David, The character of starting high/low and then stabilize some 5-30 min later is typical of oven oscillators. Underdamped ovens have been seen before, I have even seen one on the brink of oscillation. Thank you. Do you know the likely cause of the somewhat odd behaviour between about 150 and 220 s? This eBay auction, which someone posted http://m.ebay.com/itm/151256172424 says it's the high stability oscillator for an HP 8753D or 8753ES. I checked the part number at parts.keysight.comand it would appear it is the same as used in my VNA and several other microwave VNAs. That said, I have noticed a few errors on parts.agilent.com, one of which resulted in me buying the wrong part. I was later warned by Agilent not to trust the accuracy too much, especially on older equipment. It is better to check with them before making purchases. But they have a very helpful parts service that does make every effort to sort out what parts are. They spent quite some time finding out what connectors were on am obsolete cable for me. TCXO will not have the same wide range, as it compensate for the temperature. This answers my original curiosity now - did I have an OCXO or TCXO. Although I am not going to bother, as it will be easier and more accurate to feed the VNA from a rubidium or GPS locked TCXO/OCXO, it would probably be possible to buy one of those off of eBay and replace the OCXO with a better one. Then stick it in my VNA - I would not want to modify the original one. There have some rather small double oven OCXOs on eBay recently for very little money. From the earlier comments about this oscillator, it would appear its specification is quite poor for an OCXO. Cheers, Magnus Thank you. Dave ___ 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] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
As to oscillation: most older octal style crystal ovens have no proportional control at all, they are simply a bimetallic click-on-click-off thermostatic switch that is on or off, and after initial warmup they cycle up and down every few minutes. A tiny fraction of the better octal crystal ovens have some proportional heater control. Tim N3QE On Thu, Oct 2, 2014 at 2:10 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: David, The character of starting high/low and then stabilize some 5-30 min later is typical of oven oscillators. Underdamped ovens have been seen before, I have even seen one on the brink of oscillation. TCXO will not have the same wide range, as it compensate for the temperature. Cheers, Magnus On 10/01/2014 10:11 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: Further to my question the other day about what type of oscillator was used in the HP 8720D VNA, fitted with the high stability oscillator option (1D5), here is the frequency as the instrument is switched on, after being powered off for 2-3 hours. The oscillator appears to start too high in frequency, overshoots downwards, then settles down. It would be a somewhat useless exercise collecting data for much loonger and looking at in detail, since I don't know the accuracy of the HP spectrum analyzer. But that had been on for at least 24 hours. The measurement system was an HP 7 system spectrum analyzer, fitted with the 70310A precision frequency reference. This has not been calibrated in years. I will get one of those Jackson labs GPS frequency references, then I will know what the frequency is!! Assuming the crystal frequency is only a function of temperature, (and I know that not to be the case), it looks as if the oven is under damped to me. Is this behavior typical of a TCXO, OCXO or whatever ?? Any comments??? Dave ___ 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.
[time-nuts] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on
Further to my question the other day about what type of oscillator was used in the HP 8720D VNA, fitted with the high stability oscillator option (1D5), here is the frequency as the instrument is switched on, after being powered off for 2-3 hours. The oscillator appears to start too high in frequency, overshoots downwards, then settles down. It would be a somewhat useless exercise collecting data for much loonger and looking at in detail, since I don't know the accuracy of the HP spectrum analyzer. But that had been on for at least 24 hours. The measurement system was an HP 7 system spectrum analyzer, fitted with the 70310A precision frequency reference. This has not been calibrated in years. I will get one of those Jackson labs GPS frequency references, then I will know what the frequency is!! Assuming the crystal frequency is only a function of temperature, (and I know that not to be the case), it looks as if the oven is under damped to me. Is this behavior typical of a TCXO, OCXO or whatever ?? Any comments??? Dave 8720D-oscillator.pdf Description: Adobe PDF document ___ 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.
