kd7ts wrote: > Didier Juges wrote: > >> There are sudden increases in noise (bursts that last from seconds to >> minutes) on the plots I posted. >> >> I believe the sudden and drastic increase in noise at times comes from >> the GPS loosing lock. At the moment, I cannot hook up the computer to >> the GPS and verify, but I will do that later. >> > > -------- > > I have a Brooks Shera GPSDO that exhibited similar symptoms. > The phase showed huge jumps around 4:00 - 4:30 every > morning. The PLL loop might, or might not recover, but > usually didn't. I didn't have the time to spend > troubleshooting, and we seldom ran tests overnight, so I > just lived with it for more than 5 years. > > I retired recently and finally had the time to devote to > finding the problem. It was so easy, it is almost > embarassing. I picked up another GPSDO system based on a > Jupiter GPS engine and an Isotemp ovenized 10 MHz oscillator > with EFC. It was the antenna I purchased to go with this, > that turned out to be the useful missing piece of the puzzle. > > I swapped antennas between the two units to compare the SS > numbers reported by the Motorola UT+. They appeared to be > about the same, so I swapped them back. This continued for > another week or so, and I exhausted all remaining > possibilities. I swapped the two patch antennas again, but > this time I let it run for a week. I never observed the > problem during this time, so I replaced the patch antenna > (cheap) with a Symmetricomm antenna that is commonly used on > Cell sites. The system has been 100% for about 3 weeks now. > > I beleve the Symmetricomm antenna has much better filtering, > and because it has an "N" connector, I was able to use a > longer cable, with lower loss and better mounting location. > > Watching the SS numbers reported by the UT+ did not provide > any insight. They were generally between 43 and 47 and > tracking 8 with the patch antenna. I have been watching the > numbers for about 2 weeks with the Symmetricomm antenna > connected, and they show between 47 and 52 and tracking 8. > > I can only speculate on the exact mechanism, but it appears > that the system is functioning properly. > > It is the station reference for 10 and 24 GHz transverters > and a DSP-10 IF rig. > > We have 5 of these GPSDO units in the area, and all I ever > heard was, "well mine runs just fine !" > > > > Mike KD7TS > > > > That is most likely my problem. I have put the 5334B counter in parallel to the 5370A measuring the period of the 1 PPS and it clearly shows either a very stable 1 s reading pretty much down to the single shot resolution of the 5334B (10nS or so), or fluctuates by 100's of uS at a whack.
The active antenna is inside the shack, which is at the 2nd floor of my house, with a big roof over and plenty of pine trees around. I guess I will have to move the antenna and GPS receiver closer to the sky... I would rather bring the 1PPS and RSA-232 down and DC up than bring the 1.6 GHz signal down... Still, I would like to be able to detect the condition and freeze the DAC until the signal comes back (and set a warning light, with siren, cell paging, email alert and all :-) Didier KO4BB _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts