If the COM antenna is causing the GPS interference, a 1.57542 GHz notch filter (Garmin P/N 330-00067-00) may be installed in the VHF COM coax, as close to the COM as possible. This filer is not required for the GNC 4200 and GNS 430 transmitters.

Additional steps can also be taken if the COM is found to be radiating:

1. Replace or clean the VHF COM rack connector to ensure good coax ground.
2. Place grounding straps between the 400 Series unit, VHF COM and a good ground.
3. Shield the VHF COM wiring harness.