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Regular Member
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AM Radio Towers

Ok, I have what I think is a great opportunity. We are going to hang gear on AM radio towers. I have some questions for some old pros though.

As I understand, with the AM towers the entire tower, as well as rods in the ground going out every three degrees, are the antenna. Now, I know we have to have the station turn off the tower before a climber can go up.

I would think the tower is grounded because it has rods in the ground as part of the antenna..BUT.. It seems like this would ground out their signal and also allow for flow of electric current.

However it works, am I fine to hang on it just like any other tower????? Icon Question
Ancient Member
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Re: AM Radio Towers

Most AM radio towers are series fed (end fed at the bottom) and have a ceramic insulator at the base. A few smaller ones are shunt fed about 20 feet up the tower and are grounded at the base, and a variation are metal poles grounded and have wires insulated from the pole as vertical radiators.

If it's one of the second two grounded towers, you'll still have problems if you treated it as a conventional grounded mobile or cellular tower. Like changing the impedance and requiring remediation to preserves the license engineering certification.

The solution is to not change any metallic electric properties and hang a solar array and fiber media converters to get data on/off the tower if you need to do that, like for laptop access maintenance.
WHT = Short Form Acronym for "You couldn't handle me even if I came with instructions!"
Well engineered projects are indistinguishable from crazy ideas.

Speed, distance, reliability, cost...Pick three.
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Re: AM Radio Towers

My advice is run away and find an FM tower

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Re: AM Radio Towers

WHT, thanks and here is another bite of info.

I know they have had an engineer come take a "pre-reading" and afterwards he is suppose to come back and "tune it back" equal to the "pre-reading"..

So, all that being said, that we are paying to have it tuned back will this still be a problem??Will the drain wire be all I need to ground mine.. and so on??

Thanks so much!
SuperUser
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Re: AM Radio Towers

This sums up AM tower installation pretty well:

youtu.be/XcxKIJTb3Hg?t=1m25s
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Re: AM Radio Towers

I've considered installing on an AM broadcast tower which happens to be a site I maintain for the local station owner.

This one is a folded unipole antenna design, tower is grounded, radiating elements are suspended on insulators about 2 ft out from the tower (rohn 45)

I may do a test deployment over there just because I can and see how or if it will even work. another station has some STL equipment collocated there and will be moving soon, leaving behind their coax. I may try to do something single pol on that, as there will be 3 runs of 7/8" heliax left behind.

I also will have to go up the tower to remove the other stations antennas in the near future so I may drag a piece of shielded cat5 and a NSM5 up with me and link it up to my downtown site just for testing.

If I get the opportunity, I will report back with the results.

this is a 1kw full time station on 1490khz, tower is 170 ft.
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Re: AM Radio Towers

also, the pre reading and post reading mentioned earlier is of the antenna current. The license for the station will show the base current as the antenna system was designed and submitted to the fcc.
If doing anything on a series fed or shunt fed tower, a bridge meter will need to be used to measure any changes in resistance and/or reactance and the antenna tuning unit modified accordingly to present a proper 50 ohm load to the transmitter.
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Re: AM Radio Towers

As a broadcast engineer, they must not have an on staff engineer jumping up and down saying no!... As WHT said, AM towers are either series feed, or shunt fed. The entire tower radiates from bottom to top including the first area of guy wires to the first insulator. If you add anything to the tower not only must it be isolated from the tower but your equipment must be detuned to the frequency the tower is transmitting. If it is not de-tuned it will change not only the pattern of the antenna, but also change the voltage to ground readings. A small antenna can do a great deal of change to a radiation pattern on that band or the reactance of the antenna. Remember when you mount on an AM tower, you are mounting equipment on an antenna, not a tower being the entire tower is the antenna. Not to mention they will have to go off air to errect your equipment on the tower.. See if that GM would like that..lol

With that being said, if you don't isolate your gear from top to bottom including Cat 5 Cable, you will have constant RF energy going everywhere inside your equipment. I personally feel it would cost TOOOO much to operate on the broadcast tower. Now if they have an STL tower that is what you would want to be on. STL Studio to Transmitter Link.
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what ya think

Well, we are already using shielded cat6 and RF armor on all installations. All the wire will run to and the equipment be placed into a metal 3x3 shed we are building. I figure the metal roofing material on the walls and roof will help since its the same thing at my house and it is crazy hard to get a cell phone call in here(we are in town). We have also agreed to pay for the guy to come and "tune" the tower(75.00 an hour). He took a pre-reading and is being paid to come back and "re-tune" the tower.

The gm has agreed to go off air during the week. They broadcast preaching so the weekend is their big payday.

All this being said... Does this sound like it will work?? Or not?? For a couple hundred bucks it is hard to pass up a 300 ft tower in a prime location!!
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Re: AM Radio Towers

Baralak & WHT know what they are talking about
and Baralaks last paragraph sums it up well
having had some second hand experiance trying to operate on an AM tower
I still recommend you run...My guess is you will waste alot of time and money
and eventually give up anyways

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Just FYI

It is shunt fed.
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Re: AM Radio Towers

Towers with a ceramic insulator and that have obstruction lights have to get AC power to the lights. They have a ring transformer. Mount your gear on the hot side and use fiber optic media converters to bridge the gap.
Good thread,
forum.ubnt.com/showthread.php?t=16796&page=4
WHT = Short Form Acronym for "You couldn't handle me even if I came with instructions!"
Well engineered projects are indistinguishable from crazy ideas.

Speed, distance, reliability, cost...Pick three.
...World's First Ubiquiti AirMax WISP....
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I'm gonna go for it

Well, instead of getting on several AM towers I'll just stick to one. We will actually be taking ownership of this tower in 6-8 months so if it doesn't work we will turn it off and wait.

However, I talked to a redline engineer. He has been involved in deploying on an AM towers successfully. He said I have to run grounding wire up to all of my gear and tie it into the towers grounding plane I will be fine. I bet that is a $300.00 grounding wire but if it works it will pay for itself. I also have to ground my building and inside rack to the tower grounding plane.

I have two engineers( one broadcast and one wireless) that say go for it.

I guess we will see. I will report back on this one in a week or so.

Wish me luck!!!
Beau
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Re: AM Radio Towers

I do wish you good luck Man Happy and keep us posted as I have AM sites
available me but have avoided them like the plauge
do to the horror stories of previous attepts

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Re: AM Radio Towers

Good luck, and I'm glad that you have an RF engineer working with you on this project.
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Re: AM Radio Towers

We will actually be taking ownership of this tower in 6-8 months so if it doesn't work we will turn it off and wait.
If a licensed radio station is still operating, you can just turn off the power and decommission it. You have to file with the FCC for permission to decommission the license and transmitter.
WHT = Short Form Acronym for "You couldn't handle me even if I came with instructions!"
Well engineered projects are indistinguishable from crazy ideas.

Speed, distance, reliability, cost...Pick three.
...World's First Ubiquiti AirMax WISP....
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Re: AM Radio Towers

We share with an FM tower. Luckly I have turned good friends with their RF engineer and I have learned alot. Just ground the holy hell out of everything, antennas, cables, the nema boxes. Use their ground if possible. We were almost ready to give up on this tower. But right now everything is working like a champ.
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Re: AM Radio Towers

How do you ground the ubnt radios and nema boxes on these FM towers?
Member
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Re: AM Radio Towers

How do you ground the ubnt radios and nema boxes on these FM towers?


Using grounding lugs on the antennas, you'll need a large area to bond the antenna to the ground wire. The RF Engineer stated this is how you ground RF antennas and other components. We went a little bit overboard, because we were on that tower more than what we should have been. I think we may have went as far as using contact grease. We ran a separate ground wire to their FM antenna and to the transmitter. He requested for us to do this, I was scratching my head on all of this, but it worked. I would recommend using ground lugs, he said to get as much bonding surface area that you can. same thing with our nema box, use the ground lugs.
Ancient Member
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Re: AM Radio Towers

How do you ground the ubnt radios and nema boxes on these FM towers?
#6 stranded copper and galvanized crimps lugs. Just like any other bonding to a tower.
WHT = Short Form Acronym for "You couldn't handle me even if I came with instructions!"
Well engineered projects are indistinguishable from crazy ideas.

Speed, distance, reliability, cost...Pick three.
...World's First Ubiquiti AirMax WISP....
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