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Tilt on Ground Plane Antennae

Sep 9th, 08:52

N1CAK

Joined: May 10th 2018, 15:26
Total Topics: 0
Total Posts: 0
My question pertains to a 5/8 (four foot) 2 meter ground plane antenna mounted on my roof. First, I live on an island in the Atlantic. There's nothing due South until you hit Brazil and nothing due East until you hit the Azores. Because of the method of non-penetrating mounting, the mast has tilted 10 degrees to the North. To the North is Cape Cod and New England and to the West is Long Island Sound. The top of the four-foot mast is at roughly 140 feet above sea level and there is nothing North or West of me on the Island. Will the 10 degree tilt negatively affect my wave propagation?
Sep 9th, 14:36

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
A major component of the antenna pattern is the interaction with the ground. As the antenna gets higher the interaction is disturbed less by the ground, so the changed interactions due to tilt with the ground should be negligible that high up.

A bigger concern, for those who want an ideal installation, is the interaction of the antenna with the feedline and possible mounting structures.

https://forums.qrz.com/index.php?threads/rf-current-flow-on-coax-shield-od-of-ground-plane-antenna.607093/page-2

The AEA isopole decouples the shield better than most.
https://wireless-girl.com/Projects/Antennas/AEAisopole.html

It can be tedious and time consuming to accurately model the mast and feedline with an antenna modeling program, so it is rarely done.

Zak W1VT
ARRL Senior Lab Engineer
Sep 9th, 15:04

N1CAK

Joined: May 10th 2018, 15:26
Total Topics: 0
Total Posts: 0
For reference, the feedline goes down vertically and then into a window where the connector is attached to a switcher. The other antenna is a Tram 1185 mag mount mounted on the housing of the air conditioner mounted in the master bedroom window five feet away. While the feedline was manufactured 30 feet long, the antenna's distance from the transceiver is roughly 15 feet from the peak of the antenna. The line is RG8x. I do not have the tools to shorten the cable.
Sep 9th, 17:20

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
2M FM differs from HF in that with HF, relatively small improvements may allow hearing another layer of weaker stations. There are lot of modest HF stations and relatively few stations running beams on towers with amplifiers. It is possible to make a significant improvement on 2M FM and not significantly improve the number of folks you can reach. Your signal runs into a hill and won't go much farther. In some places, there is nobody else within a reasonable distance to reach.

With VHF propagation, the first 100 miles is hard. Then it gets much easier out to 250 miles. It makes more sense to think of improvements if you can reach a lot of people 100 miles away versus 50 miles away.

Many antennas require constant maintenance in a marine environment. You may want to factor that in when deciding to make changes to the antenna.

Zak W1VT

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