AM / VHF-Low Aircraft Band antenna question

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Why are AM broadcast antennas located at ground level, instead of being up high? Why do they work better near the ground?

Is this a function of the frequency range in use here, or is there more to it?

Would an antenna meant for monitoring the VHF-Low AM aircraft band also work best closer to the ground as opposed to being up high?
 

kb2vxa

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AM broadcast antennas are ground planes using earth as the counterpoise element, therefore ground conductivity is everything. That's why the favored locations are swamps and the worst are sandy or rocky soil. Then look at the size of that tower, something that big and it's radial system which is as wide as the tower is tall won't exactly fit on a rooftop.

Please explain "VHF-Low AM aircraft band" as there just ain't no such animal. There is the primary aircraft band between the FM broadcast band and the VHF high band which for all practical purposes is called VHF Hi and then there are the VHF and UHF military air bands, pick one and tell it to me. For what it's worth primary comms on the normal "VHF air band" are AM with FM commercial carrier frequencies on the high end of the band.
 

ka3jjz

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Warren I think what he means is the 108-137 Mhz aircraft band. He did sorta mix his apples and oranges there, and came up with grapefruits :.>> 73 Mike
 

Don_Burke

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PHOENIX_SCANNER said:
Why are AM broadcast antennas located at ground level, instead of being up high?
The tower is normally an element of the antenna. A quarter wave at 1500 kHz is about fifty meters.
PHOENIX_SCANNER said:
Why do they work better near the ground?
The part you can see is the vertical element of a ground-referenced antenna. There are at least 120 radials, which are usually buried.
PHOENIX_SCANNER said:
Is this a function of the frequency range in use here, or is there more to it?
I would go for the more to it option.
PHOENIX_SCANNER said:
Would an antenna meant for monitoring the VHF-Low AM aircraft band also work best closer to the ground as opposed to being up high?
No. At those frequencies, it is feasible and advantageous to elevate the driven element and the ground plane or counterpoise.

At both of our AM stations, the towers are the driven elements and they are fed against ground.

At all three of our FM stations, the antenna arrays are not ground referenced and are essentially dipole arrays fudged a bit for circular polarization.
 
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Sorry about calling it VHF-Low, it for sure is not that..lol. Mistype...


VHF Air Band 108-137...that animal.

And thanks for the responses, I never knew there were ground elements in the dirt. It all makes sense now.

Interesting that the best locations are in wet areas. No such choice around here of course, all we have is dry rocky, nasty soil. So I guess the engineers have a tough job getting optimal performance in my area.
 
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