NON Metallic Radio Towers ??

[rickharrison]

Just wondering - with the new advances in material sciences, there are strong, lightweight plastic materials that could be used to construct towers.

A neighbor of my mountain cabin has an 80' tall windmill they installed 3 years ago. (They charge a bank of batteries without - we are both off the grid there.) That tower is made of 100% plastic.

What about broadcast towers? I realize that AM towers have to conductive, but for FM and TV the antenna is mounted on a tower, but electrically isolated, right?

How much different would the antennas work if they were mounted on a non conductive structure, instead of a traditional steel tower?

Any comments greatly appreciated.

 

[fybush]

There are plenty of concrete towers out there, albeit not in the US: it's common to see freestanding concrete "masts" in Europe, perhaps even more common than the guyed steel lattice towers we're familiar with.

There are a few such structures in the US: WEBE 107.9 Westport CT, for instance, has its antenna mounted on the side of a concrete smokestack:

http://www.necrat.us/webe_pro.html

Works just fine for them...

 

[Bengalsfan]

Works just fine for them...

You would think that smokestack would give them some awful shadowing. That 30A brought back some memories.

 

[OKCRadioGuy]

OK... So here's the question of the week about WEBE: Why do they need a generator? LOL! I wouldn't think they'd ever loose it due to the fact they ARE at a power plant. Or, is it a peak power plant that's not on 24/7 anymore?

 

[foursider]

I once saw a cellular tower made of 2" X 12" lumber, laminated together, with a hollow center. Stood about 80' tall, as I remember. It was constructed to skirt a local tower ordinance that prohibited the usual steel towers.

 

[rrsounds]

Just wondering - with the new advances in material sciences, there are strong, lightweight plastic materials that could be used to construct towers.

A neighbor of my mountain cabin has an 80' tall windmill they installed 3 years ago. (They charge a bank of batteries without - we are both off the grid there.) That tower is made of 100% plastic.

What about broadcast towers? I realize that AM towers have to conductive, but for FM and TV the antenna is mounted on a tower, but electrically isolated, right?

How much different would the antennas work if they were mounted on a non conductive structure, instead of a traditional steel tower?

Any comments greatly appreciated.

No matter what it is made of, it had better have some serious metal running the full height of it for lightning protection!

My off-the-cuff opinion would be that on many levels (strength, longevity, conductivity, repairability, perhaps even cost, and not the least, the decades of experience steeplejacks have had working with it) metal is suited to do this particular job very well.

Kind Regards,
David

 

[BobOnTheJob]

From an RF radiation standpoint, it would perform very well if your goal is equal coverage in all directions. Many stations spend a lot of money in studies to make sure that the pattern distortion from a metal structure focuses their signal in a desirable direction. But some sites in the middle of a populated area might benefit from a true omni-directional pattern. A non-metallic support structure should cause the antenna to work exactly as the manufacturer rates it...+/- x number of db in free space. The lightning protection is vital...the thickest piece of wire you can afford with a 20' lightning rod on top would be a particularly wise investment with this type of structure.

 

[TomT]

Have a friend who owns a concrete tower. Used to own two of them, but sold one to A.T. & T. for a cellular installation.

These are square (about 20' X 20') poured concrete structures built in the late forties, early fifties for the first "backbone" microwave path from NY to Chicago by the original A.T. & T.

More to point of this thread, there is a telephone pole near me used for a cell tower. Not very high--about 20 feet, used undoubtedly to fill in a shadowed area along a major highway. As long as there is some path to ground for lightning strikes, the supporting material is irrelevant once you get to HF frequencies.

After all, you can (and I have) build an AM installation using insulated wire for the "ground" system. As far as the RF is concerned, there is no difference between a 1/4 wave vertical CB antenna, with 4 drooping 1/4 radials below it mounted on a pole; and a 1/4 wave AM antenna with 120 1/4 wave radials buried in the ground.

 

[nmoore6676]

Wooden, telephone type, poles are fairly common for cell phone and other two way communication antenna supports, even for hams. Probably a lot of mountain top locations have wood antenna supports for FM as well. In urban locations they probably are easier to get put up into zoned areas than more obvious structures like steel towers which would more likely require permits.

I think the original poster had the taller towers for broadcast usage more in mind though.

 

[rrsounds]

Have a friend who owns a concrete tower. Used to own two of them, but sold one to A.T. & T. for a cellular installation.

These are square (about 20' X 20') poured concrete structures built in the late forties, early fifties for the first "backbone" microwave path from NY to Chicago by the original A.T. & T.

More to point of this thread, there is a telephone pole near me used for a cell tower. Not very high--about 20 feet, used undoubtedly to fill in a shadowed area along a major highway. As long as there is some path to ground for lightning strikes, the supporting material is irrelevant once you get to HF frequencies.

After all, you can (and I have) build an AM installation using insulated wire for the "ground" system. As far as the RF is concerned, there is no difference between a 1/4 wave vertical CB antenna, with 4 drooping 1/4 radials below it mounted on a pole; and a 1/4 wave AM antenna with 120 1/4 wave radials buried in the ground.

Counterpoise antenna 'ground' and lightning protection ground are two VERY different things!

Kind Regards,
David

 

[littlejohn]

Based on the PhillyStran stuff we used to put in guy wires, I expect the cost of a plastic tower of any great height vs steel would be prohibitive.

 

[kfitz]

Our WPZX, in Pocono Pines, PA is on a very tall wooden telephone pole (approx. 80 ft. out of ground). It was pre-existing (ski resort wifi link). The pole is very large in diameter and can hold up to a thousand pound transformer...meaning an antenna that weighs a few hundred pounds is a not an issue. The location had serious zoning questions, a new tower was out of the question at the time. Had a four bay half wave antenna made to conform to RFR requirements. The mount is a "chain mount" specifically made to attach to a telephone pole (the diameter of the pole gets smaller towards the top). The chain and the brackets compensate for the changing size and make the antenna straight up and down (90 degrees) from the ground. Its been there for nearly 10 years and works well....its quite omni-directional. It can be seen from I80 in the right spot at the top of the hill west of the Blakeslee/Pocono Raceway exit.

Kevin Fitz, Shamrock Comm.

 

[Play Freebird]

Our WPZX, in Pocono Pines, PA is on a very tall wooden telephone pole (approx. 80 ft. out of ground). It was pre-existing (ski resort wifi link). The pole is very large in diameter and can hold up to a thousand pound transformer...meaning an antenna that weighs a few hundred pounds is a not an issue.

Kevin, would you happen to know how much it costs to purchase and install a pole of that size? I'm considering something like that for one of my translators. How far does it need to be buried, assuming "normal" soil?

 

[Play Freebird]

OK... So here's the question of the week about WEBE: Why do they need a generator? LOL! I wouldn't think they'd ever loose it due to the fact they ARE at a power plant. Or, is it a peak power plant that's not on 24/7 anymore?

PSEG's website has it as a "baseload, peaker" fossil plant so at least one unit may run continuously.
http://wikimapia.org/6049590/Bridgeport-Harbor-Generating-Station

Surprisingly, the signal on the back side of the stack isn't bad; I could copy WEBE near Philadelphia on a regular basis until co-channel WRNB went on the air. WEBE's original license for that site had the antenna specified as directional, but the FCC later changed it to omni.

Chriss Scherer (editor of Radio mag) was CE there in the '80s and told me he had serious issues with carbon soot settling on the antenna and causing problems. They tried enclosing the bays with radomes but the powder even found its way through joints in the plastic. I recall the problem was eventually solved by drilling a small hole in the outer conductor of the feed to each bay to "leak" a bit of dehydrated air into the radome. This would maintain enough positive pressure to keep things clean inside.

 

[Play Freebird]

Have a friend who owns a concrete tower. Used to own two of them, but sold one to A.T. & T. for a cellular installation.

These are square (about 20' X 20') poured concrete structures built in the late forties, early fifties for the first "backbone" microwave path from NY to Chicago by the original A.T. & T.

One of these (known as "Vernal") is about halfway between Buffalo and Rochester and was originally the intermediate relay point between the two cities. The top of this tower theoretically has optical line-of-sight across Lake Ontario to some of the high points northeast of Toronto. A few interesting pictures are here, some showing the old WE TD-2 radios before they were removed:

http://long-lines.net/places-routes/Vernal/index.html


A shorter version is in Cherry Valley, NY across the road from WJIV:

http://long-lines.net/places-routes/CherryValleyNY/index.html

 

[nd2023]

I don't recall that the WEBE smokestack is attached to a power plant.

Every time I've driven by that place, I see smoke coming out of the WEBE smokestack.

 

[SML]

The largest ferro-cement radio tower in the US is in Portland, Oregon:

<http://www.well.com/user/dmsml/stonehenge/index.html>

 

[Play Freebird]

On the subject of tall concrete towers, the first in the world is the Stuttgart Fernsehturm, which opened 54 years ago:

http://en.wikipedia.org/wiki/Fernsehturm_Stuttgart

Public broadcaster SWR, which owns this tower, had originally planned to construct a conventional 200 m steel structure at a cost of around 200,000 DM. In the planning stage, some of their visionary managers thought it would be nice to include an observation deck (with small restaurant/bar) and charge admission, thus the idea of the concrete tower was born -- but this would raise the cost substantially to 4.2 million DM. However, in just five years after opening, the construction cost had been completely amortized with proceeds from admission fees, and since then it's been a good income generator for the broadcaster. It's located in a public park near some soccer fields, so the visibility to nearby foot traffic probably contributes to its success. I've been up there twice and the view is quite enjoyable.

 

[DanStrassberg]

I realize that AM towers have to conductive,

No matter what it is made of, it had better have some serious metal running the full height of it for lightning protection!
My off-the-cuff opinion would be that on many levels (strength, longevity, conductivity, repairability, perhaps even cost, and not the least, the decades of experience steeplejacks have had working with it) metal is suited to do this particular job very well.

The several "towers" in each Kinstar AM antenna are wooden poles. IIRC, the center pole supports a metallic radiator. the outer poles do not radiate; they support the massive top load.

Valcom whip AM antennas are, I believe, made of Fibreglass. The radiating element is helically wound either within or on the surface of the Fibreglass structure. In addition there are center and top loads that increase the electrical length of the radiator.

I am unclear about whether a Folded Unipole AM antenna could be built on a nonconductive tower. I think so, because I think all of the RF energy that is fed into the skirt is supposed to radiate from it, but I could be mistaken about that. Nevertheless, even though a conductor may well be necessary within the skirt, I don't see why the supporting structure has to be metallic. If the structure were nonmetallic and hollow, you could run any necessary metal down through the hollow core. The dielectric constant of the nonmetallic structure would be higher than that of air, which, I believe, would lower the velocity of propagation in the skirt, making the antenna electrically taller than its physical height would indicate. But it seems as though that would be a desirable side effect of using a hollow, nonmetallic supporting structure..

 

[ChrissScherer]

Chriss Scherer (editor of Radio mag) was CE there in the '80s and told me he had serious issues with carbon soot settling on the antenna and causing problems. They tried enclosing the bays with radomes but the powder even found its way through joints in the plastic. I recall the problem was eventually solved by drilling a small hole in the outer conductor of the feed to each bay to "leak" a bit of dehydrated air into the radome. This would maintain enough positive pressure to keep things clean inside.

First, the idea to seal the radomes was not my idea. I only had the "opportunity" to live with the idea and try to make it work.

Radomes are not made to be sealed. Allowing the nitrogen to leak through a 1/16" hole in the antenna insulator and into the radome, and then out a 1/16" hole in the bottom of the (not completely) sealed radome was the general concept, but all it did was leak nitrogen like crazy.

And it wasn't just carbon soot. The antenna is mounted on a 400' smokestack, but the garbage from that stack was not the problem There are two smaller stack below the antenna that burned oil and coal.

I suggested moving the transmitter site the entire time I worked there. Moving it less than two miles inland at almost the same height would have had no effect on the coverage area.