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CarlOrton
03-26-2020, 09:06 AM
Hi, All;

I'm trying to decide on where to place the transponder antenna. This is a "regular" pre-ADSB small monopole antenna. This is going on a Zenith Cruzer, all aluminum.

My question is: How close to the edge of the structure may I place the antenna? IOW, I don't know if I need to have a minimum distance in each direction from the mounting hole, or is having plenty of room in the other 3 directions sufficient. I *know* a center-placed antenna would be better, I just don't know how much I lose with an edge-mounted antenna.

Thanks for any info you provide!

8335
FlyingRon
03-26-2020, 10:55 AM
A quick calculation would tend to indicate that 8 cm (just over 3") would be fine.
CarlOrton
03-26-2020, 03:16 PM
Thank You, Ron; may I ask how that number was calculated (I know digital. RF, ehhhhhhhh.....)
FlyingRon
03-26-2020, 03:35 PM
A quarter-wave vertical (what you have here) needs a quarterwave counterpoise. A quarterwave at 1030MHz is about 29m (neglecting velocity issues). So a quarter of that plus a little more fudge for velocity factor.
Scooper
03-28-2020, 12:35 PM
A quarter-wave vertical (what you have here) needs a quarterwave counterpoise. A quarterwave at 1030MHz is about 29m (neglecting velocity issues). So a quarter of that plus a little more fudge for velocity factor.
Ron, I think you mean a full wavelength at 1030 MHz is about 0.29 meters, so a quarter wavelength counterpoise would be 0.0725 meters, or 2.8543307 (~3) inches.
FlyingRon
03-28-2020, 08:51 PM
Yeah, 29 cm or .29m. Careless typing on my part. The answer is the same.
Frank Giger
03-29-2020, 08:06 PM
Three inches? Cool.

Why that?

* Glassy eyed stare *

Yeah, three inches. Cool.