ADS-B antenna proximity

Big Ed

N50247 - '79 Super D
Jul 20, 2020
Tampa, FL
I have a GTX-335 transponder with ADS-B Out. It connects to a small ball-and-mast antenna on my belly pan for transponder and ADS-B out broadcast.

I have installed a Stratux kit for ADS-B In. I would like to connect it to an external antenna for better reception of ADS-B towers. I bought another little TED ball-and-mast antenna from Spruce which supposedly works for both bands. The easiest place to mount it would be my belly pan. I can get about 12-18 inches separation between the two antennas. Will that cause problems?

InkedBelly pan_LI.jpg

Old Blue

Feb 13, 2020
Peterborough, NH
Hi Big ED.
Generally speaking, the absolute minimum is 1/4 of the wavelength, at least 1/2 of the wavelength is preferred. At 1000 MHz the wavelength is 0.30 meters or almost exactly one foot, so an thing over six inches is good (more is better).

On a different note, last spring my vacuum pump crapped out leaving me with the decision to replace it (again,27 yrs) or switch over and enjoy the weight loss. I went with the AV-30 installed as an AI and removed the DG as I rarely looked at it and don't fly IFR. My GPS data input is from the GPSMAP 496. I was feeling flush at the time so also installed the JPI 450 fuel scan. But be forewarned, the new fire sleeved fuel lines and fittings are going to cost almost as much as the JPI 450.

With the work all done I'm more than happy with the upgrades, both are great additions.

Sorry the attached photo is not too good, it was taken during the installation. I can't get back to the airport to get a better one due to a two week old knee replacement.