Flagpole for antenna? Resistance of concrete?

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JackJohnsrud

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I realize I'm short on theory and long on dumb novice questions. Also, I apologize for posting a second time before even finishing the first post, but this is another antenna option I'm wondering about.

I'm wondering if I might be able to use an existing 35' heavy duty steel (?) flagpole as an antenna, especially for 10 meters, if an antenna tuner is used. It is mounted with four 1" dia. bolts through a 1.5' square steel base into a 3 x 3 x 3 ft. concrete base that may or may not have footings beneath ground surface. The bolts run through about 1/2"- 4 x4" steel plates, making the steel base of the flagpole gapped from the concrete, except at the corners, by 1/2".

Is concrete a tolerable insulator? How about when wet? I wondered about coating the concrete with a rubber sealant or some kind of rubber gaskets with the bolts and plates, but am a little hesitant to unbolt it lest the concrete crack.

I thought about mounting an antenna at the top, but its awfully close to power lines, and I'm concerned it could blow off the flagpole in a fierce wind.

Suggestions? Or is it an idea only worth abandoning?

Thanks. Will catch up with you all. Glad you're out there.
 

prcguy

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I would consider the flagpole grounded, although not very well. For 10m only why not make the upper half into a J-pole, which works fine with a grounded mast. You could also ground the pole better, tap it maybe 10 to 15ft from the bottom and feed the tap with a tuner against the ground. A 35ft antenna will not have a useful radiation pattern on 10m if the entire length is the radiator but the J-pole example will.
prcguy
 

OceanaRadio

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The flagpole is COMPLETELY grounded. Steel bolts set in concrete are as perfect a ground connection as you can ask for. It is impossible to isolate such a flagpole from earth and it could never function as you suggested.

An antenna mounted on it however, could be an excellent location. That is except for the close proximity to power lines, which makes it extremely dangerous to lower/raise the entire flagpole unless you have professional talents in that regard.

You might be able to assemble two pipe-halves slightly larger than the flagpole at some elevation which you can reach from a ladder. If the block and tackle to raise a flag are still intact you could affix a short dc-ground antenna with feedline to that self-made "clamp", and run it up to the top of the pole. It will be loose and sloppy at the narrower top, but if run uip hard against the stop at the very peak it might be a solid enough ground-connection to the pole. Good enough for government work as so many say.

Jack
 

prcguy

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Grounded yes, but far from perfect as a ground to work against as a vertical antenna without radials. “Could never function as you suggested”, you talking to me? It certainly can. You can tap and match just about anything similar. Same principal as a gamma matched grounded element on a yagi, etc.
prcguy
OceanaRadio said:
The flagpole is COMPLETELY grounded. Steel bolts set in concrete are as perfect a ground connection as you can ask for. It is impossible to isolate such a flagpole from earth and it could never function as you suggested.

An antenna mounted on it however, could be an excellent location. That is except for the close proximity to power lines, which makes it extremely dangerous to lower/raise the entire flagpole unless you have professional talents in that regard.

You might be able to assemble two pipe-halves slightly larger than the flagpole at some elevation which you can reach from a ladder. If the block and tackle to raise a flag are still intact you could affix a short dc-ground antenna with feedline to that self-made "clamp", and run it up to the top of the pole. It will be loose and sloppy at the narrower top, but if run uip hard against the stop at the very peak it might be a solid enough ground-connection to the pole. Good enough for government work as so many say.

Jack
 

OceanaRadio

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prcguy said:
Grounded yes, but far from perfect as a ground to work against as a vertical antenna without radials. “Could never function as you suggested”, you talking to me? It certainly can. You can tap and match just about anything similar. Same principal as a gamma matched grounded element on a yagi, etc.
prcguy
I was responding to the original poster but your comment about the pole "not being well grounded" was incorrect. It seems you only meant it was not ready to efficiently radiate a vertical antenna without adding radials.

The poster asked if he could use the flagpole itself (which he mistakenly assumed was isolated from ground) as the radiating element. He wondered what it's electrical length would be effective on. The entire mast is grounded and no part of it will radiate, except into the ground. Something else attached to the pole is anothermatter of course.

Jack
 

prcguy

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But a grounded radiator will radiate just fine with no degradation compared to an isolated flagpole. You can tap it and tune it for a single band with a gamma match or use an auto tuner for multiband operation if done right. The J-pole example also uses the actual grounded pole as the radiator and you can make the same flagpole into several single band J-poles for the upper HF bands and use them simultaneously.
prcguy
OceanaRadio said:
I was responding to the original poster but your comment about the pole "not being well grounded" was incorrect. It seems you only meant it was not ready to efficiently radiate a vertical antenna without adding radials.

The poster asked if he could use the flagpole itself (which he mistakenly assumed was isolated from ground) as the radiating element. He wondered what it's electrical length would be effective on. The entire mast is grounded and no part of it will radiate, except into the ground. Something else attached to the pole is anothermatter of course.

Jack
 

OceanaRadio

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prcguy said:
But a grounded radiator will radiate just fine with no degradation compared to an isolated flagpole. You can tap it and tune it for a single band with a gamma match or use an auto tuner for multiband operation if done right. The J-pole example also uses the actual grounded pole as the radiator and you can make the same flagpole into several single band J-poles for the upper HF bands and use them simultaneously.
prcguy
A J-Pole does not use the grounded element as its radiator. It is a vertical dipole antenna with a tuning element, a grounded element, and a radiating element. If wires or pipe-elements were added to a grounded flagpole to convert it into a J-Pole, the grounded flagpole will not be the radiating element, it is the grounded element.

As for gamma-matching ("tapping without isolating"), that is an art of hobbyists derived from boredom no doubt, as it is the least efficient method of radiating anything. It assumes a tap in the middle of a one-ended grounded element will let some radiation "leak" above the tap, and balance the other side to ground. Efficiency rating? Apparently of no concern to those who are thrilled that it "works".

Jack
 

prcguy

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The J-pole radiating element is grounded as is countless other radiating elements everywhere you look, were surrounded by them. If that is part of the design, it has no bearing on the performance of the antenna. It’s probably not practical to scale the 35ft flagpole and transform it into a J-pole but if low freq HF is a consideration I would still tap the pole at maybe 10 to 15ft from the bottom and feed it with an auto tuner against some ground radials.
prcguy
OceanaRadio said:
A J-Pole does not use the grounded element as its radiator. It is a vertical dipole antenna with a tuning element, a grounded element, and a radiating element. If wires or pipe-elements were added to a grounded flagpole to convert it into a J-Pole, the grounded flagpole will not be the radiating element, it is the grounded element.

As for gamma-matching ("tapping without isolating"), that is an art of hobbyists derived from boredom no doubt, as it is the least efficient method of radiating anything. It assumes a tap in the middle of a one-ended grounded element will let some radiation "leak" above the tap, and balance the other side to ground. Efficiency rating? Apparently of no concern to those who are thrilled that it "works".

Jack
 
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