On Thu, 29 Nov 2018 21:22:44 -0700 Mark Goldberg <marklgoldb...@gmail.com> wrote:
> How much could I expect ADEV to improve if I move the antenna to a better > location with clear view of the sky? The things I am testing need to be > better than 8e-10, so this at just under 3e-10 may be "good enough". Moving > the antenna would involve drilling a hole in the outside wall, so it is not As Bob already wrote, antenna position is only one thing. But if your receiver is going into holdover at all, then you are already in a place where you will not have good enough reception to get down to your requirement. Antenna position, ie sky view and multipath, are the two things that kill most of the performance of any GPSDO. Bad sky view can result in several µs of phase variation and multipath in several 100ns. After that, you will need a local oscillator with sufficient stability to average over a long period. To get below 1e-10 you will need to average over at least 100s (given good receiver and perfect antenna position), better make it 1000s to 10ks. This means, the local oscillator has to be stable enough to stay below 1e-10 over that period. Which means you need to use a good OCXO at the very least, in a temperature stable environment. No-one of the GPSDOs you mentioned fullfills that requirement. (The NV47* of the TruePosition is decent, but falls slightly short. Leo's GPSDO uses a TCXO) I would recommend you to get either a Thunderbolt (first choice) or a Star4 (second choice) from ebay. Alternatively, get one of Nick Sayer's GPSDO, modify it to use a good OCXO and crank up its loop time constant. Do not get one of the Trimble UCCM, they have quite horrible frequency jumps. Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neal Stephenson _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.