Said - To date there has been no data taken just on the EFC to see if there is any correlation. However, late last year a test was run for about 11 days on the Mini-T, without the antenna connected, and a slow downward drift was evident. In fact, the drift was such that the 11 Hz requirement, at 30 GHz, was easily met even though there may have been noise on the EFC. Like I said previously, I am in the process of fighting the 11 Hz requirement as I believe it is totally unrealistic. Even the spec of 1 KHz is unrealistic at the high data rates being used. But, since that can be easily met, at least for the time being, I am not ready to tackle that issue. I did receive one of those 1938A units from Rick, but have not had a chance to play with it yet.
I think I mentioned in a previous post that John did contact me over the weekend and told me he retired 2 years ago. Now he is too involved with his new post as President of the IEEE starting in 2009. I was hoping he could help me fight this battle. We worked on some of the same issues together on and off in the last 25 or so years. I would definitely be interested in your unit. I assume then that it was also for a terminal to be used with the AF WGS satellite. Regards - 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 [EMAIL PROTECTED] Sent: Thursday, October 16, 2008 12:40 PM To: time-nuts@febo.com; [EMAIL PROTECTED] Subject: Re: [time-nuts] Frequency Stability of Trimble Mini-T Hello Mike, Tom, just came across your post. This looks to me like a classical crystal frequency jump that the unit is compensating for. Looks like the Mini-t is a bit under-damped in it's response. John Vig talks about these jumps in his paper, and he mentions that the root causes are not well understood. One way to verify this is to plot the EFC voltage (not sure if this can be done on the Mini-t), and see if it "jumps", similar to the plots in the Vig paper. Co-incidentally we have developed a unit for this same Army requirement (11Hz requirement), and early on had seen a similar issue which we solved, and we can now easily meet this requirement. Let me know if you would like more details, we can provide these offline. Typically crystals jump <1ppb, but I have seen worse. That busts the 11Hz requirement of course. With GPS disciplining, these jumps can now easily be seen. "Curing" the jumps is a combination of crystal blank processing, testing, burn-in, and other factors. There is no easy solution. You actually have stumbled upon an area where, as well documented as Quartz oscillators are, there is quite a lack of documentation and research in my opinion. One note: some of the time nuts had received E1938A' units that had tags on them saying "crystal jumps", so this problem happens in the best families :) bye, Said In a message dated 10/14/2008 17:13:04 Pacific Daylight Time, [EMAIL PROTECTED] writes: Tom - Thanks for your reply. I was not present during the testing. In my opinion, and now I have been able to convince others, the contractor passed the test, which is derived from MIL-STD-118-164ACN2. The main specification states the following: 5.1.2.5 Carrier frequency accuracy. The carrier frequency accuracy at the antenna feed shall be within 1 KHz of the intended value for all RF carriers. Recalibration intervals to maintain this accuracy shall not be less than 90 days. This is on an Army satellite terminal. Another branch of the Army came up with the 11 Hz requirement over 24 hours (for testing purposes), which is just 1KHz/90, and I feel it is total rubbish. I myself have been trying to find out the gate time used on the counter, but have not been abler to get it yet and not sure I will. Needles to say, using the stated counter, and logging a measurement at one minute intervals with a resulting readout down to 1 Hz at 30 GHz, probably does not leave too many options for gate time. The jumps do not exactly come in pairs, although they seem to, but, remember there are close to 16,000 points on that graph. I agree with you that averaging would make the plot into a straight line. _______________________________________________ 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.
