Hi Jay,

I'm a freelance Avionics Tech. in southern CA. I find your post interesting. The GS is a separate antenna then the VOR/LOC. Are you sure the GS bug is swinging or just the CDI. If both GPS units are doing same swing than most likely problem is in the antenna, splitter or coax wire in between. Not difficult to test, remove your Garmin units out of rack and use a volt meter to ohm the center conductor of the coax, the resistance should be fairly low. I don't recall the specs from memory but less than 50 ohms rings a bell. Also, you may have a second splitter near the NAV antenna, check that too. Antennas need a good airframe ground to work properly, make sure there is no coorosion under ant base. NAV ant  is located on vertical stab either a blade that sits parallell to the ground or cat wisker type ant. On a 210 the Glide slope antenna is usually mounted inside the airplane, a clear flat plexiglass plate mounted at the top of your windscreen. Don't forget about your static wicks, if they are not working properly the airframe could be developing a charge in flight (that would usually cause poor comm performance too).

Randy Wilson
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