At least for the T-bolt moving the antenna to a super-optimal location is a super waste of effort and money. I suspect this applies to most other GPS DOs.
Unless you can compare the phase of the 10 MHz with a local Rb or Cs (or a good crystal) you cannot learn much more or provide better than the short term accuracy of the receiver. Improving on this will require a good local standard running open loop. The location should provide tracking of a few satellites - more than 4 if possible - but it will remain locked with as few as 1 or 2. The glitches you see will always occur as the receiver switches satellites and cannot be avoided with even the most perfect antenna location. So the short term ADEV presented by LH jumps around. Fooling around with the damping factor and time constants will not help this much. Set the DF to 1 and the TC to 200 seconds and leave it there. (or something like those values) The way to get a good standard is to open loop (using you fingers) adjust a local Rb such as the LPRO so it maintains a constant phase difference with the GPS 10 MHz for a period of hours. Using the time for the phase to change a measured number of nanoseconds, the frequency offset between the two is easily calculated. There is a HP ap note on how to do this. Use the GPS calibrated local open loop standard for all critical work - not the GPS output. Due to lightning considerations here is Kansas - my GPS antenna is in the front yard at 6 ft elevation and the N.E FOV is shielded by a 3 story house. Result is that the phase as plotted on a strip chart recorder is unchanging for hours relative to my Rb, but the flat plot shows phase jumps from time to time when the receiver shifts satellites. However the long term phase jump always returns to the previous value after the jump. To make further progress you need a good open loop local standard like the LPRO and some way to measure the 10 MHz Phase difference and record it over a period of hours. As to using the pps - I don't know much about doing it that way - however it seems obvious that the 10 MHz phase is more sensitive and faster due to the greater update rate. I could be wrong! Best regards and don't put the thing on the tower. Total waste of effort. Get a Rb. Do protect the receiver from rapid temp changes - -73 john k61ql _______________________________________________ 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.
