Garmin GTN 750xi vhf issue

[fly1981]

We have just completed an avionics upgrade in our baron. The package included a garmin gtn750xi, which is used as com 1. I have noticed the range of vhf communications when using com 1 is shocking, in some instances 20 miles. Switch over to com 2 which is a 20 year old 430, and transmitting and receiving is crystal as clear. Any idea what could be causing this?

[Chalkie]

RF is a real black art/witches craft. I would take the aircraft back to the avionics shop and ask them to fix it.

However if you want to do your own fault finding, I would disconnect the coaxial RF cable at both ends and check for continuity and for a short circuit from centre core to shielding. It is quite easy when crimping the centre pin to the centre core of the coaxial, to misplace one strand and this strand could then short out the centre core to the shielding. This could result in the shielding becoming the RF radiator and not the antenna.

If coaxial is good, then try to swop Comm 1 and Comm 2 coaxial cables at the back of the radio trays, so as to have each use the other antenna. This way you can see if it is a transmitter problem or an antenna problem.

Have fun crawling under the panel...

[fly1981]

Thanks for the response Chalkie, I think it’s best I take it back to the shop that did the installation…

[porsche1662]

Thanks for the response Chalkie, I think it’s best I take it back to the shop that did the installation…

Good morning. I have the EXACT same issue. all new everything. 750xi and a 430. I have to use 430 as my #1 rather than my back up.
Replace coax last month and same issue. Switched antennas and still same result.

Did you find out the issue ?

[pietern]

Joint Beechtalk.com and go to the "Panel Talk" section. They have a active discussion on this topic under "GTN 750Xi Reception issues - Help". I'm sure you will find good pointers there.
Good luck.