[time-nuts] Delay through GPS antenna splitter/amplifier -- an answer, and a question

[John Ackermann N8UR]

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