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Antenna Engineering Question

Help with installing an Antenna, or just choosing the right antenna to go with your radio, or your mobile.

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RodinKy
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Antenna Engineering Question

Post by RodinKy » Tuesday, 09 May 2017, 7:36 AM

This may be a stupid question, but why is the gamma match always on the bottom of a vertical mounted beam, it would seem like it would work better on top, any ideas or theories?


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443 Arizona
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Re: Antenna Engineering Question

Post by 443 Arizona » Wednesday, 10 May 2017, 5:39 AM

dont you mean, "why is it always on the beginning and not the end" of the antenna? (just trying to help) :icon_e_wink: now that i have confused this, my work is done, :bounce:

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Re: Antenna Engineering Question

Post by MDYoungblood » Wednesday, 10 May 2017, 6:32 AM

This is a really good question and my only answer I can come up with is the designer drew it up that way and the manufacturer built it to the designer's specs. If you look at other brands of beams most are on the bottom element but a few have it on top, the old Wilson was on top, Mosley who is the manufacturer of the Maco antennas has them on top of their 11m beams as well. Years ago when I had a Moonraker IV I tried both ways, didn't see any difference so I left it on top, (too lazy to climb the tower again :lol: ).

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sonoma
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Re: Antenna Engineering Question

Post by sonoma » Wednesday, 10 May 2017, 6:44 AM

my thoughts were that with the gamma rod turned up it would be easier for water to get inside and damage it . I know most have a seal on them but a few years in the sun the rubber would crack. just my thoughts on this.

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The DB
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Re: Antenna Engineering Question

Post by The DB » Wednesday, 10 May 2017, 7:32 AM

Why do you think putting it above the element would be better?

The thing is it is so close to the element that it doesn't really matter. You can put it above, below, in front or behind the element, or anywhere else around the element for that matter, and you won't see a difference performance wise. Electrically these are all pretty much the same.

Beam antennas are generally fed from the bottom, that is the direction the coax comes from, so mechanically it is easier to build an antenna that way, that is pretty much it.

Also, many beams used on other bands are fed on different sides. I have a 2 meter beam that is fed from the top, although it uses a beta match. I have also seen them that are fed from the front (beam direction) of the driven element.


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RodinKy
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Re: Antenna Engineering Question

Post by RodinKy » Wednesday, 10 May 2017, 14:52 PM

Thanks for the replies, I just wondered after looking at pics of beams why they were mostly on the bottom element. Good answers all of them.

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Re: Antenna Engineering Question

Post by MDYoungblood » Friday, 12 May 2017, 9:35 AM

I think on an antenna like the Moonraker the engineers put the gamma matcher on the bottom of the vertical driven element so it could compensate for the mast being seen as part of the antenna and might make for easier tuning.

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