Re: [time-nuts] HP 1938 revisited
J. L. Trantham wrote: Thanks for the info. My plan is to develop a stable GPS disciplined reference suitable for use as a reference for Microwave work in the 10 GHz range that can be used in portable locations with relatively quick start up. Perhaps the 1938 would be better in the shop where it could be left on for weeks/months at a time and an LPRO 101 or a 10811 could be used for the portable application. Reasonably high drift rates could be accommodated if the GPS signal is reliable and the time constants (disciplining rate, drift rate, etc.) are appropriate. Thanks, Joe The advantage of the E1938A over the 10811 is that it has very low tempco, which comes into play in the holdover mode (no GPS). If you always have GPS, you might as well just use a 10811. The 5071A cesium clock uses a 10811 that is disciplined all the time. There would be no advantage in replacing it with an E1938A. The loop in the 5071A is fairly slow, but would be considered fast by GPS standards. If the portable location involves severe temperature fluctuations, then possibly the E1938A could make sense. Rick Karlquist N6RK E1938A designer ___ 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] HP 1938 revisited
Fluke.l (China) was selling a number of 1938's on Ebay. I snagged one just to have a piece of HP history. It works just fine, but I've noticed something a little strange. Comparing the 1938 to both my cesium and GPS standards, there's a distinct periodic 1ns phase shift every second. Seems to smoothly advance 1ns for 500 ms, then retard back to the original phase point over the next 500ms. Question: is this to be expected? I'm assuming this is from the AFC loop, but I would have expected it to be better damped. I've searched both this group and the HP group; there really doesn't seem to be a great deal of info about these, other than schematics and some nice variance plots on leapsecond. Just what is the serial port and the PIC data lines useful for, if anything? -- Bill Ezell -- They said 'Windows or better' so I used Linux. ___ 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] HP 1938 revisited
wje wrote: Fluke.l (China) was selling a number of 1938's on Ebay. I snagged one just to have a piece of HP history. It works just fine, but I've noticed something a little strange. Comparing the 1938 to both my cesium and GPS standards, there's a distinct periodic 1ns phase shift every second. Seems to smoothly advance 1ns for 500 ms, then retard back to the original phase point over the next 500ms. Question: is this to be expected? I'm assuming this is from the AFC loop, but I would have expected it to be better damped. The AFC loop (as opposed to EFC) is a purely analog loop in which there is no mechanism for a 1 Hz oscillation. Now if you are talking about the EFC, that is another story. Depending on how you are driving the EFC, you can pickup noise from any number of sources. I vaguely remember there was an LED that flashed at 1 Hz if everything was working OK. You might see if that is the source of what you are seeing. I've searched both this group and the HP group; there really doesn't seem to be a great deal of info about these, other than schematics and some nice variance plots on leapsecond. Just what is the serial port and the PIC data lines useful for, if anything? The serial port can be used to change the oven temperature set point and IIRC monitor various oven parameters. Probably nothing you want to play with if you want a working oscillator. If you want to experiment, I have released the software to talk to the serial port. It should be archived somewhere. In production, we ramped the temperature up and down and found the exact turnover temperature for each individual oscillator and set the oven to the turnover. This required that we make crystals that actually had a turnover. Many 10811 crystals did not have turnovers, only an inflection point. Rick Karlquist N6RK Designer of E1938A ___ 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] HP 1938 revisited
I, too, snagged one of these since it has the reputation of being the ultimate achievement of crystal oscillator technology with the goal of building a GPS controlled reference using a Brooks Shera controller card and a GPS receiver. Toward that end, since it takes a few minutes for the 1938 to 'lock', is there a signal that can be used to 'turn on' disciplining? It doesn't seem logical to try to discipline the oscillator until it has stabilized and, therefore, if the device is to be used from time to time, not staying on continuously, it will need a way to optimize turn on performance. Thanks in advance and I would appreciate any 'links' to any programs that would allow communication with the oscillator. Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Richard (Rick) Karlquist Sent: Sunday, April 12, 2009 6:33 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] HP 1938 revisited wje wrote: Fluke.l (China) was selling a number of 1938's on Ebay. I snagged one just to have a piece of HP history. It works just fine, but I've noticed something a little strange. Comparing the 1938 to both my cesium and GPS standards, there's a distinct periodic 1ns phase shift every second. Seems to smoothly advance 1ns for 500 ms, then retard back to the original phase point over the next 500ms. Question: is this to be expected? I'm assuming this is from the AFC loop, but I would have expected it to be better damped. The AFC loop (as opposed to EFC) is a purely analog loop in which there is no mechanism for a 1 Hz oscillation. Now if you are talking about the EFC, that is another story. Depending on how you are driving the EFC, you can pickup noise from any number of sources. I vaguely remember there was an LED that flashed at 1 Hz if everything was working OK. You might see if that is the source of what you are seeing. I've searched both this group and the HP group; there really doesn't seem to be a great deal of info about these, other than schematics and some nice variance plots on leapsecond. Just what is the serial port and the PIC data lines useful for, if anything? The serial port can be used to change the oven temperature set point and IIRC monitor various oven parameters. Probably nothing you want to play with if you want a working oscillator. If you want to experiment, I have released the software to talk to the serial port. It should be archived somewhere. In production, we ramped the temperature up and down and found the exact turnover temperature for each individual oscillator and set the oven to the turnover. This required that we make crystals that actually had a turnover. Many 10811 crystals did not have turnovers, only an inflection point. Rick Karlquist N6RK Designer of E1938A ___ 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] HP 1938 revisited
J. L. Trantham wrote: I, too, snagged one of these since it has the reputation of being the ultimate achievement of crystal oscillator technology with the goal of Thanks, we thought it was pretty good :-) Toward that end, since it takes a few minutes for the 1938 to 'lock', is there a signal that can be used to 'turn on' disciplining? It doesn't seem logical to try to discipline the oscillator until it has stabilized and, therefore, if the device is to be used from time to time, not staying on continuously, it will need a way to optimize turn on performance. There is nothing in the E1938A that locks. The closest to lock is the oven current cutting back. After that, the oven will settle within a few minutes to its set point. However, the crystal will exhibit high aging rates for hours. It will not get back to the aging it had when last turned off for something like a day. During this recovery time, you can discipline the oscillator if you like, but it won't give very good holdover performance if you lose GPS. No crystal oscillator will give the kind of performance you need for this application unless it is continuously ovenized. The SC cut is a big improvement over the AT cut in terms of a cold start, but is still not adequate for GPS work right after a cold start. Hope that helps. Rick Karlquist N6RK Designer of E1938A ___ 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] HP 1938 revisited
Thanks for the info. My plan is to develop a stable GPS disciplined reference suitable for use as a reference for Microwave work in the 10 GHz range that can be used in portable locations with relatively quick start up. Perhaps the 1938 would be better in the shop where it could be left on for weeks/months at a time and an LPRO 101 or a 10811 could be used for the portable application. Reasonably high drift rates could be accommodated if the GPS signal is reliable and the time constants (disciplining rate, drift rate, etc.) are appropriate. Thanks, Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Richard (Rick) Karlquist Sent: Sunday, April 12, 2009 7:57 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] HP 1938 revisited J. L. Trantham wrote: I, too, snagged one of these since it has the reputation of being the ultimate achievement of crystal oscillator technology with the goal of Thanks, we thought it was pretty good :-) Toward that end, since it takes a few minutes for the 1938 to 'lock', is there a signal that can be used to 'turn on' disciplining? It doesn't seem logical to try to discipline the oscillator until it has stabilized and, therefore, if the device is to be used from time to time, not staying on continuously, it will need a way to optimize turn on performance. There is nothing in the E1938A that locks. The closest to lock is the oven current cutting back. After that, the oven will settle within a few minutes to its set point. However, the crystal will exhibit high aging rates for hours. It will not get back to the aging it had when last turned off for something like a day. During this recovery time, you can discipline the oscillator if you like, but it won't give very good holdover performance if you lose GPS. No crystal oscillator will give the kind of performance you need for this application unless it is continuously ovenized. The SC cut is a big improvement over the AT cut in terms of a cold start, but is still not adequate for GPS work right after a cold start. Hope that helps. Rick Karlquist N6RK Designer of E1938A ___ 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.
