Separation of VHF Antennae

JDCAVE · Feb 9, 2016

Ok ok, you say "antennas" and I say "antennae". It's the biologist in me. Insects have two "antennae".

So I have currently have a Shakespeare VHF antenna on an extender pole, I believe it goes up 16'. I would like to mount a second antenna, a Shakespeare 5225XT, about 14-16" away on the flybridge combing. This link here suggests verticals separation achieves more than horizontal separation, so I may be ok.

How close can I mount two VHF/UHF antennas | KB9VBR J-Pole Antennas

Any thoughts on this issue?

Jim
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Paul Swanson · Feb 9, 2016

The information in the link is correct. The radiation pattern of a vertical dipole antenna (like yours) is primarily in a plane perpendicular to the antenna axis, that is, parallel to the water. Not much radiation goes directly up or down. Therefore another antenna above or below will have minimal interaction. However, the 16' pole supporting the first antenna can interact with the second antenna if it is metal. If it is fiberglass there should be no problem.

Paul

JDCAVE · Feb 9, 2016

Thanks Paul the support "pole" is fiberglass, and is made by Shakespeare. Just how thick is that "doughnut"? Is it the entire length, or situated more near the top?

Jim
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markpierce · Feb 9, 2016

Don't know. Regardless, my single VHF antennae works.

denverd0n · Feb 10, 2016

The "doughnut" is pretty thick, and the signal radiates from the entire antenna. It extends above and below the antenna, also. As such, you still want some vertical separation, if you can get it. Wikipedia has a pretty good explanation of dipole antennas, including a diagram of the radiation pattern... https://en.wikipedia.org/wiki/Dipole_antenna

Separation of VHF Antennae

JDCAVE

Guru

Paul Swanson

Veteran Member

JDCAVE

Guru

markpierce

Master and Commander

denverd0n

Guru

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