I have a white-hockey-puck style active GPS antenna, probably about 1998 vintage with no markings except 'Made in Mexico'.
While compensating for cable delay is relatively straight forward by measuring the length and compensating for the velocity factor, a question is: how much amplifier / filter group delay is to be expected within the antenna itself? I'd assume that the amplifier in the antenna probably has pretty small group delay, but the RF filter may be significant. Looking through GPS SAW filter datasheets seems to show none with group delay specifications. googling leads to some research papers with delays of about: L1 - 20 MHz wide SAW filter has about 15 nsec of group delay L1 - 2 MHz wide SAW filter has about 65 nsec of group delay L1 - LC filter - can't find anything, but suspect it's probably just a few nanoseconds. I'm not sure a consumer grade antenna even has a SAW filter, it may simply be an LC filter. If it does include a SAW filter, then just using cable delay alone would seem to underestimate the actual antenna delay compensation needed for GPSDO, perhaps significantly. Has anyone on the list measured or otherwise estimated the active antenna delay including the amp and filters? -- Tom, N5EG _______________________________________________ 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.
