About a year ago I had 430 installed in my Arrow. My second Comm radio is a Collins 251. However, when I transmit on the Collins it causes the 430 to drop off line, i.e., loses satellite acquisition. The shop that installed the 430 has tried everything they can think of to correct this but nothing works. As a result I cannot use the Collins radio to transmit, especially if on an instrument approach using the 430. This avionics shop said my case is not unique.
Has anyone else experienced this problem? If so, have you found a fix?
Have they tried a filter? Either a bandpass filter in the gps antenna, or a notch filter in the com output? Beyond that, the best course is probably to replace the radio with something better behaved.
They didn't install it properly. The GPS and #2 comm antenna are simply too close. THe whole subject and how to avoid this are contained in the Garmin install manual. It should have never been released because there is a specific test for this that has to be done before you can sign the install off as airworthy. Make them do it over correctly. There is a notch filter that can help, but only if the antennas are not too close together. There should be at least 3 feet between the GPS and the comm 2 antenna. Satellite drop during radio transmission is a critical error that is a known problem, and that is why Garmin tells you how to avoid it while installing their equipment.
Replacing the radio isn't a cure because it isn't the radio's fault. It is an antenna issue.
The test for freq interferance is not always conclusive. Another thing to check is re-radiating interfence from the ELT. Disconnect the ELT, either at the antenna or the ELT and try transmitting from your #2 VHF. If this fixes the problem, the ELT needs to be replaced, something you'll want to do anyway. Some have fixed this problem by trimming a few inches off the ELT antenna but I don't advocate this as there is no basis for approval.
