Definitely sounds like the RF is getting into the GPS input stage &
blocking its signal.
What sort of access do you have to the GPS antennae connection. Can you add
a trap such as a 1/4 wave ( at ~145MHz) length of short circuited coax. -
Or even a simple hairpin coil across the input terminals may have enough
inductance to be insignificant at the GPS frequency. e.g - 20mm wire ~20nH
? = 188 ohms (~1dB)at 1.5GHz, v/s 18.2 ohms (~7.7dB) at 145MHz. - Maybe not
enough - a 1/4 wave trap would be much better..

Otherwise - maybe you could mount the GPS antennae directly below the 2m
one so the VHF signal pickup is minimal.
Or is there a waveguide type filter you could place over the GPS antennae
to attenuate low frequency pickup.?

Richard P



    This is an interesting issue. I made several tests yesterday, and
when the GPS is in the floor of the garage, the system works! As i put
it in higher places the interference goes getting higher until the same
high of the radio's antenna, when the transmitted signal gets muted!


    I think it's a mag antenna. It's mounted in the top of the car roof.

Rafael.

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