Hello all:
I am an electronic technician with 30+ years experience fixing computers. In my spare time I like to play with old computers and electronics. Recently I got bit by the precision timing bug, partially after running across the wonderful leapsecond.com site, which lead me here. First I got a FE-5680A, then after reading some of the archives here I bought a Nortel / Trimble 45000 GPSDO and still later a used Thunderbolt-E. My main interest in these devices at this time is for a accurate bench top frequency source, however I do have a 59309A running off of each of the GPSDOs. I am wondering if they will drift apart, but I suspect I will need to wait a long time to see evidence of that. I set them simultaneously by setting them both to the same GPIB address and connecting them to the same bus on my HP-86B, this works well for setting them but I have to remember to disconnect one or change the address on one before I try to read them. MY question concerns the thunderbolt-E, I have been using LH to monitor both of the GPSDOs and was quite surprised to see that the Nortel 45000 seems to perform much better than the thunderbolt-E, I thought that the E being a newer device it would perform better. I will admit that I have a much less than ideal antenna setup however the antenna location is the same for both devices, they are only a couple feet apart. The antenna's are a Trimble magnet mount antenna and a the dome antenna that came with the thunderbolt-E kit. Initially I had the magnet mount attached to the Nortel and the dome antenna attached to the E, but I have now swapped antennas but it has not made any difference , and I am beginning to wonder if my E is in fact defective. I have been in contact with one other person who has an E and his experiences have been similar to mine, even though he has a much better antenna setup, so I would like to ask if there is anyone else out there with an E, and ask the group for comments on what I am seeing. My observations have been that the 10MHz is not very stable, on LH I will see relatively large spikes in the DAC voltage that of course impacts the 10MHZ, I had it connected to my 5316A counter that was running with the FE-5680A as a timebase, with a 10 second gate time and logging counts with my 86B and I was seeing excursions og over 100Hz which I guess percentage wise is not huge but I do not see anything like that on the Nortel. Now some of these excursions do occur when there are satellite switches, and if they all occurred coincident to satellite switches I would mark it up to my crummy antenna arrangement, but they don't they occur even when the satellite tracking is stable and often come in groups of several transition first positive followed by an equal transition in the negative direction. There is also a constant chatter of about 100uV on the DAC line as reported by LH which also translates to noise on the OSC and PPS lines, my technician sense thinks that looks like power supply noise, but I have not looked under the hood yet. One really annoying thing I have noticed is the E reports having saved my location, however it apparently has not so every time it resets for whatever reason it goes into a self survey, which because of my less than ideal antenna setup usually takes some time to complete, even a warm reset resulted in it losing it location and entering self survey. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
