intermittant comm static

[9Driver]

RV-9A with a Garmin 300 GPS/COMM. Began having comm static in proximity to towered airports. Within 2 miles of airport instant static that lasts until 1/3 to 1/2 mile from landing. Squelch has no effect and it seems to only occur on lower freqs below 123.0. Upper freqs are OK. Static does not build in intensity - it is either there or gone. RMI? antenna mounted on top of fuse just behind canopy (slider). Any ideas anyone? Do not have the problem at my home base (non-towered).

[fmarino1976]

From your description of the problem, it appears to be related to proximity to the airport. The only thing I can think of that COULD cause interference like that is the tower's primary radar. Check the antenna grounding. I have seen similar problems in helicopters when the antenna is too close to the plexiglass "chin-bubble". In those cases we had to relocate the antenna to areas with a better ground plane.
Are all your audio wires shielded? Are they grounded properly? PS-Engineering recommends grounding only one side of the shields. I hope some of this info helps.
Let us know what you find.

[9Driver]

If airport primary radar was the culprit, wouldn't the static come and go as the radar antenna rotated?