Hi By far the simplest way to do this is to use a broadband passive antenna with a short cable. They are a $10 item on the auction sites. Compare whatever comes out of the GPS running off the cheap antenna to your “full system” pps offset. What you are doing with this comparison is no different than the VNA approach. You are just using real GPS signals in your real environment to run the test. If the only delta is the delay in the cable / antenna amp / filter / distribution amplifier (antenna locations are the same) then it all should work out.
Simply put: 1) Attach gps to simple broadband antenna with short cable. You may have to play some tricks to get the antenna current detect to stop complaining. A Tee connector and a resistor are generally all that takes. 2) Measure pps offset to a local standard (possibly a GPSDO on another antenna) 3) Attach gps to real antenna and what ever cable, (at the same location as the simple antenna) 4) Measure pps offset to the same standard 5) Repeat the process until you are convinced the results make sense. I’d do at least 5 loops to be reasonably sure. If you have enough gear, you can compare multiple receivers and antennas all at one time. Swap around the antennas and “stuff”. Ultimately you will come up with relative numbers for each item. This all assumes you are running timing grade receivers with sawtooth data. It also assumes you have a counter that’s good enough to collect the data. Since all that it way cheaper than a fully calibrated microwave VNA, I don’t think that is a terribly crazy assumption. Does this matter for a “frequency nut” - nope. Will it make your GPSDO work better -nope. Could it get you slightly closer to UTC - yup. Bob _______________________________________________ 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.
