Rob Kimberley wrote: > Interesting paper. I agree that for nanosecond timing applications then > antenna cable and matching are important. However, for frequency sync > applications and non-critical timing, then the effects of the 75 vs. 50 ohm > cable will not be noticeable. > > Rob K > > >>> Those who maintain that its OK to use 75 ohm GPS antenna cable should >>> read: >> http://tf.nist.gov/timefreq/general/pdf/1384.pdf >> >> Bruce >> Except that just as varying multipath delays as satellite elevation changes have an effect on the timing receiver output that is equivalent to a frequency shift, the diurnal variation in the cable propagation delay with temperature will also affect the timing error due to reflections caused by cable mismatch. Thus the effect of the diurnal variation of the cable propagation delay will thus have a complex effect on the timing receiver PPS output timing. Variations in PPS output timing are equivalent to frequency modulation of the PPS output.
If one is trying to achieve the frequency disciplining performance that even single frequency GPS carrier phase tracking is capable, then such effects are significant particularly if one is using the difference between the phase and group velocities in the ionosphere to correct for the propagation delay through the ionosphere. This is one reason why it can be a good idea to stabilise the antenna and cable temperatures. Bruce _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts