In a message dated 12/25/2006 06:18:57 Pacific Standard Time, [EMAIL PROTECTED] writes:
In my own GPSDO i discipline the LO's pps to have a MAXIMUM phase offset of 500 ms against the receiver's pps. That avoids lots of ambiguity problems and leaves the widest phase measurement range to make the loop even lock when the OCXO is initially far apart its setpoint. Otherwise you are correct that one can optimize for different parameters. This gives immediate rise for the following publications: 1) A guide to discipline your frequency source to a phase source with minimum phase offset 2) A guide to disipline your frequency source to a phase source with minimum frequency offset 3) A guide to discipline your frequency source to a phase source with best phase stability 1) A guide to discipline your frequency source to a phase source with best frequency stability If you can deliver or send some links: I will surely devour stuff like this! Best Regards Ulrich Bangert, DF6JB Hi guys, this brings us to an interesting discussion: what is more useful: * best frequency accuracy * or best phase lock (minimum 1PPS phase offset to UTC). We have one customer at Jackson-Labs telling us most implementations prefer frequency accuracy over phase accuracy since these units are often used in the field to drive frequency counters, signal generators, and receivers etc, that don't require tight phase offsets, but rather need a very accurate frequency. It's a trade off of short-term frequency stability (lower for best phase performance) or long term frequency stability, with longer phase drifts away from UTC but better overall frequency accuracy. I suspect the time nut's would rather have a very accurately locked 1PPS to UTC and don't mind larger short term frequency offsets needed to steer the 1PPS onto the UTC 1PPS. When doing frequency measurements, one would prefer to always have the most accurate frequency possible. Two different settings in the loop performance are required here. On our Fury GPSDO, we allow the user to set the loop parameters by hand (with some suggested defaults) to optimize the unit to be either tightly locked, or more loosely locked to UTC. We also have two OCXO options available to address the problem: a double oven high-stability unit that can be much more loosely coupled, and a more cost-effective single oven that wants to be tightly controlled by the GPS with higher short-term frequency wandering. On top of the ADEV loop time constants cross-over point discussion Ulrich described, it's also a question of how much UTC (as delivered by the GPS) phase offset these units can achieve in say 1-Sigma measurements (<5ns and <<15ns respectively typically). bye, Said _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
