Re: [time-nuts] Follow-up on Z3801A high EFC reading
John: If it was turned off for more than a year, in my experience, the HP10811 (or similar) oscillators at the heart of the Z3801A will take about three weeks to settle down, and rejoin the previous mature aging curve. I have built a few GPSDOs using HP10811 oscillators, that I bought off of eBay, and they all took three weeks to settle down. You can ask the experts on the list why. Something about temperature related stress relief and gas sublimation on the surface of the crystal. --- Graham == On 7/16/2011 3:39 PM, John Ackermann N8UR wrote: Last week I posted about one of my Z3801As having a very high EFC reading and an EFC ERR message in the health status when powered up again after about 18 months of sleep and a 500 mile location change. Over the last week, the error message has continued, but the EFC has consistently trended downward. It started out at about 1015000 and is now down to 1012070. During the first day or so, the EFC count was going down more than one unit per minute; in the last day or so, it's more like 4 or 5 units per hour. But since it's moving in the right direction, I'm not going to try to rip open the outer oven at this point. This sort of aging effect is a bit odd given that this unit had been running continuously for about 7 years before it was shut down for the move; I might expect to see this is in a brand new unit but not in one with so much running time. I've been comparing the 10 MHz output against a cesium during this time, and an ADEV plot is attached. It seems to indicate that the performance is just fine -- the short term floor is probably limited by the 5061B's noise, and we can see the 5061A long-term noise floor starting to show up at 200K seconds, but there's certainly nothing here to question the performance of the GPSDO. Now that I've captured this baseline data, I'm going to power cycle the Z3801A to see if it lands in the same general vicinity. John ___ 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] Follow-up on Z3801A high EFC reading
One crystal expert, who's name escapes me, sorry, told me that if you power up an oscillator that has been off for an extended period, you should expect a very rapid ageing process to occur with a lot of the accumulated changes that would have happened had it been powered on then to occur when it was restarted. But I can't quote chapter and verse, obviously. Dan ac6ao ___ 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] Follow-up on Z3801A high EFC reading
Hi John and Graham, On 16/07/11 22:50, Graham / KE9H wrote: John: If it was turned off for more than a year, in my experience, the HP10811 (or similar) oscillators at the heart of the Z3801A will take about three weeks to settle down, and rejoin the previous mature aging curve. I have built a few GPSDOs using HP10811 oscillators, that I bought off of eBay, and they all took three weeks to settle down. You can ask the experts on the list why. Something about temperature related stress relief and gas sublimation on the surface of the crystal. I was just about to make this point. While I am not an expert in crystal oscillators (I think I can name at least 4-5 people here with their hands dirty from it) from what I have read up and from what I have seen the type of re-trace properties you describe is typical. It is to avoid this re-trace that instruments keep their oscillators oven heated in stand-by mode. If you look for it, you will find the effect well covered in literature. There are several mechanisms in play, but polution depositing on the crystal surface is one of them that I've heard of. Mechanical stress as the temperature change causes re-shaping of all mechanical aspects and the forces it puts on the crystal blank until realigned again is another. So, that was in the back of my mind when I said that you should wait. For a crystal of 10811 class weeks is to be expected before saying it is bad or badly out of tune. Anyway, good to hear about the progress. The EFC track-in cruve looks like expected from this type of event. Notice that you might need to use a curve-fit cancellation matching the drift curve. ADEV is sensitive to drift and isn't particularly gifted in illustrating the drift either. I could dig up a few references for you if you badly need it. 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] Follow-up on Z3801A high EFC reading
I think it is in Matthys, Crystal oscillator circuits. Can't quote page number now, as my verson is somwhere I cant remember. It's an excellent book if you do some experimentation. I did write an letter to R.J. Matthys a couple of years ago, and reveiced an answer. 73 de Thomas LA3PNA/AE5YS. 2011/7/16 Dan Rae dan...@verizon.net: One crystal expert, who's name escapes me, sorry, told me that if you power up an oscillator that has been off for an extended period, you should expect a very rapid ageing process to occur with a lot of the accumulated changes that would have happened had it been powered on then to occur when it was restarted. But I can't quote chapter and verse, obviously. Dan ac6ao ___ 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. -- Please avoid sending me Word or PowerPoint attachments. See http://www.gnu.org/philosophy/no-word-attachments.html ___ 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] Follow-up on Z3801A high EFC reading
Thomas, Dan, Magnus, Graham -- Thanks for the replies! This is an interesting example of no two oscillators are the same. I certainly expected that there would be aging and retrace on a cold oscillator, but I started both Z3801As almost simultaneously and within about 12 hours unit #1 had stabilized and the EFC was showing normal noise over a fairly small range with no real trend apparent. But unit #2 (the one shown in the plots) continued to have the very pronounced aging trend of after 12 hours, with one click per minute more than a day after power-on, as well as having a much higher absolute EFC value than it did before, or than unit #1 has now. So, based on unit #1, I was suspicious of what was going on in the second unit. It may just be that #2 doesn't have as good an oscillator as #1. John Thomas S. Knutsen said the following on 07/16/2011 05:32 PM: I think it is in Matthys, Crystal oscillator circuits. Can't quote page number now, as my verson is somwhere I cant remember. It's an excellent book if you do some experimentation. I did write an letter to R.J. Matthys a couple of years ago, and reveiced an answer. 73 de Thomas LA3PNA/AE5YS. 2011/7/16 Dan Raedan...@verizon.net: One crystal expert, who's name escapes me, sorry, told me that if you power up an oscillator that has been off for an extended period, you should expect a very rapid ageing process to occur with a lot of the accumulated changes that would have happened had it been powered on then to occur when it was restarted. But I can't quote chapter and verse, obviously. Dan ac6ao ___ 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.
