Hi Remember - OCXO's are going to be acceleration sensitive. As you bump about on back roads, the oscillator is likely moving around by a few ppb. If you are after a hertz at 10 GHz, that's a lot.
Your GPS will be off by a fairly predictable amount based on it's idea of it's location. If you have a 3M position accuracy, then you will likely have 10 ns of time error. With a 10 second loop, you are right back to a ppb. A good Rb should be able to hit a sub ppb accuracy at 10 minutes. No perfect answer. Bob On Mar 10, 2013, at 10:23 AM, Jim Lux <[email protected]> wrote: > Asking here on behalf of a friend.. > > With respect to portable amateur microwave operation.. you want good close in > phase noise (so you can use narrow band filters) AND good frequency accuracy > (so you can find the signal)> > > the typical operation is "drive somewhere, operate a bit, drive somewhere > operate a bit" repeated (contacts from different grid squares/peaks/what > haveyou" > > My instinct is that this is an application for a nice quiet OCXO on a > battery. Adjust the frequency before you set out against a good reference > and just go from there. > > Surplus Rb references are apparently also popular, but I think they keep > those on battery too (that is, you need to be ready to go 10 minutes after > arriving, and I don't know that a Rb is "settled in" that quickly). > > So the question from my friend was with reference to GPS disciplined > oscillators. Would that do any better? I'm used to GPSDOs in a fixed > location where you have time to do long term averaging. > > And what about truly mobile operation (there are folks in the SF bay area > apparently doing 10GHz mobile ops.. slotted WG radiator on the roof of the > car, etc.) > > What sort of 1pps timing accuracy do you get from a GPS "on the move". I > assume it would have the usual 10ns sort of uncertainty (in that the mfr > specs don't say "only with the antenna fixed in one place for N hours"). > 10ns is only 1E-8 of a second. Presumably one can average a bit over many pps > ticks. > > > I've got a bunch of Wenzel Streamline units, and they typically do 1E-10/day > aging and 1E-9 over temp. Assuming the temperature doesn't vary a "lot", > seems like the OCXO is "better" than the GPS, at least in a 1-2 day time > frame. (and, of course, isn't that just what a GPSDO is, in holdover mode, > anyway) > > The Rb is good to 1E-11 over the short run (assuming it's been "calibrated" > recently) but I notice that the PRS10 data sheet says 7 minutes to 1E-9, so > in the "non continuously powered" mode of operation, it's not all that > wonderful. > > > The Rb is definitely higher powered.. The PRS10 is 2+ amps at 28V to start, > and 0.6 to run. 15-16 Watts is a lot to keep on a battery. (Assume you run > off a pair of 7Ah 12V batteries.. that gives you 10-12 hours). > > The Wenzel is a couple watts (after a 5W warmup). The GPS is a LOT lower > power. The Garmin GPS 18x is 0.45W, of course the 1pps on that receiver is > only specified to 1 microsecond.. A moto Oncore UT is a bit less than a watt > and claims <100ns (with SA.. showing the age of the datasheet I have). > > > _______________________________________________ > 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. _______________________________________________ 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.
