I have 2 antennas mounted on opposite ends of a roof and both of them feed commercial GPS DA/splitters and I can have as many as 10 receivers running at one time for testing. I have also used one of the high frequency type F TV passive splitters with one D.C. feed through and added 200-300 ohm resistors from the other outputs to ground. All this has seemed to work just fine but one of the older receivers apparently radiated its L.O. out the antenna coax and would interfere with a couple of other receivers I connected to the same DA. Connecting one 10 Mhz references to the external trigger on my scope and feeding 2 other GPS receivers to the input channels (all from the same antenna DA), I can watch the slow drift at 2 ns/div with respect to the trigger and sometimes one receiver drift one way as the other receiver drifts in the opposite direction and sometimes they drift the same way. The drift is generally less than 2 ns but it is there and I assume it depends on what the internal ‘housekeeping’ of the receiver is doing and what birds they are using. So bottom line, they aren’t ‘locked’ to each other but are generally close. -Arthur

Hi As the “filter” (or control loop) in some GPSDO’s scales, it impacts the degree of “agreement” between the GPSDO’s. Not all GPSDO’s scale filters so not all exhibit the behavior. The HP / Symmetricom Z38xx units are one family that do this kind of scaling. As the scale moves longer (time) or narrower (frequency) the ADEV improves. This also depends a bit on the quality of the OCXO you have and the environment the GPSDO is in. Somewhat counter intuitively, the level of agreement gets worse as the ADEV improves. As the time agreement gets worse and ADEV gets better, the frequency accuracy (in the frequency nut sense) gets better. Again - not all GPSDO’s do this sort of thing. Bob > On Nov 17, 2017, at 5:15 PM, Arthur Dent <golgarfrincham@gmail.com> wrote: > > I have 2 antennas mounted on opposite ends of a roof and both of them feed > commercial GPS DA/splitters and I can have as many as 10 receivers running > at one time for testing. I have also used one of the high frequency type F > TV passive splitters with one D.C. feed through and added 200-300 ohm > resistors from the other outputs to ground. All this has seemed to work > just fine but one of the older receivers apparently radiated its L.O. out > the antenna coax and would interfere with a couple of other receivers I > connected to the same DA. > > > > Connecting one 10 Mhz references to the external trigger on my scope and > feeding 2 other GPS receivers to the input channels (all from the same > antenna DA), I can watch the slow drift at 2 ns/div with respect to the > trigger and sometimes one receiver drift one way as the other receiver > drifts in the opposite direction and sometimes they drift the same way. The > drift is generally less than 2 ns but it is there and I assume it depends > on what the internal ‘housekeeping’ of the receiver is doing and what birds > they are using. So bottom line, they aren’t ‘locked’ to each other but are > generally close. > > > -Arthur > _______________________________________________ > 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.

Hello Arthur, Might be interesting to try the same experiment both with the two receivers on the same antenna and on the two different antennas. In an ideal world I'd expect the time output(s) to track as well either way, but it would be interesting to know how well this works out in practice. Dana K8YUM On Fri, Nov 17, 2017 at 4:15 PM, Arthur Dent <golgarfrincham@gmail.com> wrote: > I have 2 antennas mounted on opposite ends of a roof and both of them feed > commercial GPS DA/splitters and I can have as many as 10 receivers running > at one time for testing. I have also used one of the high frequency type F > TV passive splitters with one D.C. feed through and added 200-300 ohm > resistors from the other outputs to ground. All this has seemed to work > just fine but one of the older receivers apparently radiated its L.O. out > the antenna coax and would interfere with a couple of other receivers I > connected to the same DA. > > > > Connecting one 10 Mhz references to the external trigger on my scope and > feeding 2 other GPS receivers to the input channels (all from the same > antenna DA), I can watch the slow drift at 2 ns/div with respect to the > trigger and sometimes one receiver drift one way as the other receiver > drifts in the opposite direction and sometimes they drift the same way. > The > drift is generally less than 2 ns but it is there and I assume it depends > on what the internal ‘housekeeping’ of the receiver is doing and what birds > they are using. So bottom line, they aren’t ‘locked’ to each other but are > generally close. > > > -Arthur > _______________________________________________ > 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. >

When I first powered them on together, they seemed to drift all over the place with regards to relative phase. For the past hour now, they are keeping around 7 degrees and sometimes dropping to around 4. I think that is pretty amazing given all the stuff between the source and final display. I have the cursors on them now and they are sitting at 2ns difference. I am going to figure out how to plot this possibly using Timelab and my HP 5371a. > On Nov 17, 2017, at 2:29 PM, Bob kb8tq <kb8tq@n1k.org> wrote: > > Hi > > As the “filter” (or control loop) in some GPSDO’s scales, it impacts the degree > of “agreement” between the GPSDO’s. Not all GPSDO’s scale filters so not all > exhibit the behavior. The HP / Symmetricom Z38xx units are one family that > do this kind of scaling. > > As the scale moves longer (time) or narrower (frequency) the ADEV improves. > This also depends a bit on the quality of the OCXO you have and the environment > the GPSDO is in. Somewhat counter intuitively, the level of agreement gets worse > as the ADEV improves. As the time agreement gets worse and ADEV gets better, > the frequency accuracy (in the frequency nut sense) gets better. > > Again - not all GPSDO’s do this sort of thing. > > Bob > >> On Nov 17, 2017, at 5:15 PM, Arthur Dent <golgarfrincham@gmail.com> wrote: >> >> I have 2 antennas mounted on opposite ends of a roof and both of them feed >> commercial GPS DA/splitters and I can have as many as 10 receivers running >> at one time for testing. I have also used one of the high frequency type F >> TV passive splitters with one D.C. feed through and added 200-300 ohm >> resistors from the other outputs to ground. All this has seemed to work >> just fine but one of the older receivers apparently radiated its L.O. out >> the antenna coax and would interfere with a couple of other receivers I >> connected to the same DA. >> >> >> >> Connecting one 10 Mhz references to the external trigger on my scope and >> feeding 2 other GPS receivers to the input channels (all from the same >> antenna DA), I can watch the slow drift at 2 ns/div with respect to the >> trigger and sometimes one receiver drift one way as the other receiver >> drifts in the opposite direction and sometimes they drift the same way. The >> drift is generally less than 2 ns but it is there and I assume it depends >> on what the internal ‘housekeeping’ of the receiver is doing and what birds >> they are using. So bottom line, they aren’t ‘locked’ to each other but are >> generally close. >> >> >> -Arthur >> _______________________________________________ >> 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.