Swept frequency plots to determine potential immunity to 1240 to 1300 MHz interference. It is desired to use both of the GPS antennas in the proximity of 1240 to 1300 MHz 10 watt transmitters. Conclusion: Don't get your 23 cm antenna too close to your GPS antenna. Greater than 6 feet seems to be OK from several installations checked, no de-sense of received GPS satellites. I'll measure exact levels when I get the antennas installed on the vehicle.
An HP8714ES network analyzer was used to transmit a signal to GPS antenna and preamplifier. A non-resonant antenna was used as the signal source. DC power was applied to the GPS antenna thru a bias tee. Output of bias tee run back to network analyzer. Each of the tested antenna/preamplifiers have about 24 db gain (specified). It was assumed that some of the filtering in the GPS antennas is ahead of the preamplifier section but that is not really the case as the patch antenna only provides about -15 dbc of filtering with respect to the 1575 level.. The amplitude is not calibrated in these plots as the only desired response was frequency and relative attenuation. The shape of the GPS passband was also somewhat subject to antenna(s) position and should only be taken as approximate. Jpeg plots are about 80k.
HP 58504A antenna:
(below) Patch antenna and 1st preamplifier only.
(below) Complete unit response.
Axiom GPS antenna:
de N6CA 11.2003