I had a chance recently to look at the performance of the two-port and eight-port HP GPS antenna splitters on a super-duper network analyzer. Screenshots of the results are at http://www.febo.com/time-freq/pages/gps-splitter.
In short, the minimum delay (at the center of the passband) from antenna port to output port is around 15 nanoseconds for the eight way unit, and about 22 nanoseconds for the two way one. The delay seems consistent on all the ports, with less than 1 nanosecond variation. However, there is also a hump in the delay near the edges of the passband, about 12 MHz above and below the center. The delay at the edges increases by perhaps 5 nanoseconds, though depending on the port, it's not always symmetrical. So, an interesting question for any of you *real* GPS experts is what effect a variation in group delay of the RF input has on the timing solution? Is the true "length" of the amp/splitter some average of the delay across the passband, or, given the spread spectrum nature of the signal, does it not really matter? In fact, is the "length" of the splitter even related to the measured group delay? This also raises the issue that any GPS antenna that has RF filtering is likely to have similar delays; I've never seen that sort of data published. John _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
