GPS Antenna Cable Delays at N8UR

I measured the electrical length of the two GPS antennas using an Agilgent 8712ES network analyzer. These measurements are from the clock-room ends of the LMR-400 cable that connect to the two distribution ampliers. For fun, I used two methods to measure the delay: Remember that the additional delay of the distribution amplifier as well as the cables from the amplifier to the GPS receiver need to be included in the delay calculation. See the further notes below, based on measurements on two HP GPS splitters that we did a few years ago.

GPS Antenna 1 -- Aeroantenna

The cable fault length of 134.16 feet equates to 136.43 nanoseconds. Taking one half of the mean delay of 273 nanoseconds, we get 136.5 nanoseconds. The two measurments correspond well.

This antenna is connected to an HP 58517A 8-way splitter, which has about a 14 ns delay. So, with that in mind, I am using a cable delay of 140 ns at the splitter outputs for this system.

GPS Antenna 2 -- Motorola Timing 2000

For this antenna, the 139.88 foot electrical length corresponds to a delay of 142.24 nanoseconds, and the delay measurement gives us 142.0 nanoseconds. I'm not sure why the peak-peak noise is so much greater on this delay measurement than for the other antenna; the measurements were taken within a few minutes of each other using exactly the same instrument settings.

This antenna is connected to an HP 58535A 2-way splitter, which has about a 22.5 ns delay. So, with that in mind, I am using a cable delay of 165 ns at the splitter outputs for this system.