Has anyone ever got one of these approved with the FCC for their main AM antenna not an STA? It would seem to me that if the FCC wanted to "save" AM (and the fees) they would allow these to cut down on the land requirements especially for Class C and D AM's.
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Isotron AM Antennas
- Thread starter secondchoice
- Start date
I don't think anybody's tried the Isotron antennas on medium wave.. I'm not sure they can meet the minimum radiation requirement but they seem to work great on the ham bands
Yes people have.. and I was one of them , along with the GM of a station several years. We couldnt get it to tune up, even with an antenna tuner... but we were low on the band. the might work ok on the upper end of the band, but so would a long wire, it'd probably work better!!
We ended up letting the smoke out of the tuner and the AM is now gone.
The are many AM stations with poor (to almost non existing grounding systems). The station I had in mind is on 1400. 99% of there listenership is on their FM translator. The tower is too frail for cellular rental. The ground system is at least 50 years old. The land has some value. The Commission is not going to give a STA because you sold the land. But if you could use 10% of the land sell the rest and be legal, it could be a good thing. BTW there are no opportunities to duplex..
There are ways to have a good ground without buried radials, such as counterpoise on the roof or a folded dipole. The folded dipole is used by many of the old Class IV stations so that they can also put cellular and communications antennae on the tower or to avoid ground issues.
I think several operators who post here have folded dipoles so perhaps they can give more info.
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KIUL was using a folded dipole when I was there. Worked great. They were blessed with really good ground conductivity. This tower really needs upgraded to handle any kind of extra weight. The guys are very rusted but the tower itself has good paint. There is an airport very close so it has lights, another expense.
Forgive me for asking here, but are these antenna systems true folded dipole systems or actually folded unipole systems?
There most likely are other companies that do this but I personally have only work at two stations that have used Nott.
Here his his explanation:
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Don't have much experience with folded unipoles; but have had dealings with consulting engineers with vastly different opinions about them. Both consultants were well known and very well respected. One claimed in the right conditions, they perform quite well. The other claimed they amounted to unsubstantiated voodoo science, and lacked the performance of a proper height vertical antenna and groundplane. Remember, ground is 50% of your antenna. Doesn't matter what the frequency.
As I thought, the link is for a folded unipole.
I did work at one station which had a folded unipole system and although the ability to cross the base insulator with the FM
and two way radio feedlines with much less of a problem was neat, what I thought more was that the antenna system seemed to be far less prone to transmitter issues from lightning - mostly the lack of off-ons due to lightning, as the tower was grounded.
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That is the problem. A lot of class C's and D's have deteriorated ground systems.
The Isotron is not suitable for standard broadcast use as it will not meet minimum radiation standards. You CAN get away with it under an STA for temporary/emergency use, because all you need to do is radiate SOME type of signal to maintain on-air presence. I have one station using one now under those circumstances, but that is the only way one is "legal" on AM. As someone said, you can't cheat physics, but you can manipulate it sometimes. The folded unipole is a great antenna for many applications, and can be utilized to great capability in many cases. It can be used on a shorter than normal tower, and made even shorter by top loading, and still radiate to minimum FCC standards. The counterpoise is the key to making minimum, and that can be done with an elevated counterpoise. I am one of the leading consultants on both unipoles and elevated counterpoise, and have built several stations using both. I have recently developed a new technique of shortening the physical length of the radials to half what they would normally be, but still maintaining a full 90 degrees electrical length, so that drops the land use area by 50%. And if the station is non-directional, only four radials are needed to satisfy the FCC. On directionals they really want to see six. While I am always searching for the "fairy dust" that can make an AM antenna perform in the minimum amount of physical space, I (nor anyone in the past 100 years) have yet to find that magic key. But I have found the best hacks available, and they work and are FCC accepted. See the linked Radio World article.
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Exactly, thank you.
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