Bruce Posted December 2, 2015 Report Share Posted December 2, 2015 Wondering if anyone else has had, or heard of anyone else having a loss of intregrity while transmitting on comm radio. Problem just recently started, intermittant, and only on certain frequencies (121.0 and 120.9 that I can recall). When it does happen, push the PTT switch and immediate LOI. Release the PTT switch and immediate Integrity Restored. Each time at the avonics shop, can't duplicate. Ben, my avionics guy, says to take notes on when it happens so we don't get into a parts changing mode to troubleshoot the problem. But most likely an antenna problem. Did send the 480 back to Garmin for complete once over. No change. Thoughts and ideas would be appreciated. Bruce N231CH Quote Link to comment Share on other sites More sharing options...
N601RX Posted December 2, 2015 Report Share Posted December 2, 2015 Certain com channels have frequency harmonics that fall in the GPS band and is know to cause these problems. If you look in especially the older GPS install manuals you will see a page that instructs the installer to transmit on certain com frequencies and verify that the GPS is not affected. Some radios have cleaner output than other. There is a coaxial filter available that is susposed to help. RG400 coax and keeping the com and GPS coax as for away from each other as possible will help. Connecting the offending radio to a bottom mounted antenna is also a possibility. Example from kln94 install manual F.Select the AUX 2 page, verify that no asterisks appear next to any satellite with an elevation greater than 25°. Select 121.15 MHz on COMM 1. Transmit on COMM 1 for a period of 20 seconds and verify that no asterisks appear indicating satellites with an elevation of greater than 25°. Repeat for the following frequencies: 118.000, 120.925, 121.175, 121.200, 123.825, 127.100, 130.625, 131.250, 131.275 131.300 and 134.150 MHz. Repeat the above procedure for all VHF COMM’s on board the aircraft. If any of the above tests do not pass (any asterisks appear on satellites with greater than 25° during the above tests), it will be necessary to identify the source of the interference. There are two common sources of interference: 1.The 12th and 13th harmonics of the above mentioned frequencies can be radiated from the VHF COMM at a level strong enough to be a problem to the GPS but still be well low enough to meet TSO/JTSO requirements for the VHF COMM If the interference is from the radiating VHF COMM, an optional notch filter (i.e. the KA 198 P/N 071-01565-0000 or TED Mfg 4-70-54) will need to be installed. The recommended location for the inline filter should be as close to the VHF RT as practical. NOTE The conditions and tests performed on this article are minimum performance standards. It is the responsibility of those desiring to install this article either on or within a specific type or class of aircraft to determine that the aircraft installation conditions are within these performance standards. The article may be installed only if further evaluation by the applicant documents an acceptable installation and is approved by the Administrator. 2.The other possibility is re-radiation from an ELT. The radiated RF from the VHF COMM can excite the output tank circuit of the ELT and cause it to oscillate and radiate RF strong enough to interfere with the GPS. If disconnecting the ELT antenna eliminates the GPS interference, the manufacturer of the ELT should be contacted for a recommended solution. Quote Link to comment Share on other sites More sharing options...
DonMuncy Posted December 2, 2015 Report Share Posted December 2, 2015 14 minutes ago, N601RX said: Certain com channels have frequency harmonics that fall in the GPS band and is know to cause these problems. If you look in especially the older GPS install manuals you will see a page that instructs the installer to transmit on certain com frequencies and verify that the GPS is not affected. Some radios have cleaner output than other. There is a coaxial filter available that is susposed to help. RG400 coax and keeping the com and GPS coax as for away from each other as possible will help. Connecting the offending radio to a bottom mounted antenna is also a possibility. Example from kln94 install manual F.Select the AUX 2 page, verify that no asterisks appear next to any satellite with an elevation greater than 25°. Select 121.15 MHz on COMM 1. Transmit on COMM 1 for a period of 20 seconds and verify that no asterisks appear indicating satellites with an elevation of greater than 25°. Repeat for the following frequencies: 118.000, 120.925, 121.175, 121.200, 123.825, 127.100, 130.625, 131.250, 131.275 131.300 and 134.150 MHz. Repeat the above procedure for all VHF COMM’s on board the aircraft. If any of the above tests do not pass (any asterisks appear on satellites with greater than 25° during the above tests), it will be necessary to identify the source of the interference. There are two common sources of interference: 1.The 12th and 13th harmonics of the above mentioned frequencies can be radiated from the VHF COMM at a level strong enough to be a problem to the GPS but still be well low enough to meet TSO/JTSO requirements for the VHF COMM If the interference is from the radiating VHF COMM, an optional notch filter (i.e. the KA 198 P/N 071-01565-0000 or TED Mfg 4-70-54) will need to be installed. The recommended location for the inline filter should be as close to the VHF RT as practical. NOTE The conditions and tests performed on this article are minimum performance standards. It is the responsibility of those desiring to install this article either on or within a specific type or class of aircraft to determine that the aircraft installation conditions are within these performance standards. The article may be installed only if further evaluation by the applicant documents an acceptable installation and is approved by the Administrator. 2.The other possibility is re-radiation from an ELT. The radiated RF from the VHF COMM can excite the output tank circuit of the ELT and cause it to oscillate and radiate RF strong enough to interfere with the GPS. If disconnecting the ELT antenna eliminates the GPS interference, the manufacturer of the ELT should be contacted for a recommended solution. I sure am glad I don't need to understand all that. 1 Quote Link to comment Share on other sites More sharing options...
helitim Posted December 2, 2015 Report Share Posted December 2, 2015 We had almost this exact issue on the 152. We sent the comm back to the factory for a bench test and they were unable to duplicate the problem. Neither was the avionics shop able to duplicate. The fourth trip to the avionics shop I insisted that they check the antennas and wiring and they found the base of the antenna where it mounted to the plane was severely corroded to the point that it was causing intermittent loss of contact. Cleaned the antenna base, and problem was eliminated. Point being, don't overlook the small stuff when trouble shooting. This may have nothing to do with your problem but our symptoms were just the same. Quote Link to comment Share on other sites More sharing options...
larryb Posted December 2, 2015 Report Share Posted December 2, 2015 What kind of comm radio? KX155 is famous for this behavior. Quote Link to comment Share on other sites More sharing options...
Bruce Posted December 2, 2015 Author Report Share Posted December 2, 2015 The GPS is a Garmin 480, and the comm radio is a KY197. Both work great, otherwise. Another clue to this LOI issue is that when the "ghost" is in the airplane, I can almost forcast a loss of integrity because the comm feedback in the headset sounds like you are talking into a hollow log and the ATC's reception of the transmission is not good, in which case I switch to the KY197 which transmission is then normal. The next step looks like to remove the antennas and be sure of a good ground plane. Bruce Quote Link to comment Share on other sites More sharing options...
Brandontwalker Posted December 3, 2015 Report Share Posted December 3, 2015 I had a very similar issue arise a few weeks ago. The difference was that I was having troubles with transmission and reception. I had one radio bench tested and it failed. Second radio bench tested good. Replaced the failed radio, but the problem persisted. Checked the screws on the ground plane for the accessible antenna, sprayed with contact cleaner and ran the screws in and out a few times to assure that any corrosion was broken up. Still no joy. To my embarrassment, it turned out to be the charger for my Ipad causing the issue. Unplugged it and all is well. If you have any 12v devices plugged into the accessory port/cigarette lighter try to unplug them and see if that resolves the issue for you. 1 Quote Link to comment Share on other sites More sharing options...
M20S Driver Posted December 4, 2015 Report Share Posted December 4, 2015 8 hours ago, Brandontwalker said: I had a very similar issue arise a few weeks ago. The difference was that I was having troubles with transmission and reception. I had one radio bench tested and it failed. Second radio bench tested good. Replaced the failed radio, but the problem persisted. Checked the screws on the ground plane for the accessible antenna, sprayed with contact cleaner and ran the screws in and out a few times to assure that any corrosion was broken up. Still no joy. To my embarrassment, it turned out to be the charger for my Ipad causing the issue. Unplugged it and all is well. If you have any 12v devices plugged into the accessory port/cigarette lighter try to unplug them and see if that resolves the issue for you. I had comm issues on my GNS530 with my Stratus if the Stratus external antenna was connected and was mounted near the radios. Quote Link to comment Share on other sites More sharing options...
Bruce Posted December 5, 2015 Author Report Share Posted December 5, 2015 Thanks to everyone who responded. I will work through the recommendationsand post my findings. This Mooneyspace is amazing. Thanks again. Bruce Quote Link to comment Share on other sites More sharing options...
Retz Posted December 6, 2015 Report Share Posted December 6, 2015 Wondering if anyone else has had, or heard of anyone else having a loss of intregrity while transmitting on comm radio. . Bruce N231CH Loss of integrity on the radio? I thought that was when you bust through an ATC assigned altitude on climb out and they ask "confirm you are at 190 as assigned"...you turn off mode C and say "Affirm 190" Sent from my iPad using Tapatalk 1 Quote Link to comment Share on other sites More sharing options...
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