Reviving a dormant antenna system

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Joe Friday
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Reviving a dormant antenna system

Post by Joe Friday » Sat Feb 11, 2017 3:18 am

I am in the process of working on a CP for a facility that has been off the air since 2001. The CP is at the same location, class, and ERP as the original, and they would like to make use of the the old antenna and feedline. The system comprises a 4 bay ERI HP rototiller, end fed, and approximately 675' of Andrew HJ8 heliax. The antenna was installed in 1983, and the line was replaced in about 1995 or so after being shot by an idiot plinking at the tower lights and suffering a burn out.The system has not been pressurized or had power on it for at least 10 years. ERP is 28KW, TPO will be about 16KW.

I have not yet looked at the system in any way, but plan to do so shortly. I would suspect that the line has some water in it at this point. I thought I would begin with a look at the system with a SA/TG and return loss bridge, and depending on how that looked, put a small amount of power into it and see what happens.

Any thoughts or suggestions would be appreciated. I have made them aware that the coax may need to be replaced, but if we can avoid this $30-$40K hit it would be great, as money for the project is tight (when is it not?)

Thanks,

Kevin

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Deep Thought
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Re: Reviving a dormant antenna system

Post by Deep Thought » Sat Feb 11, 2017 5:23 am

Anything that has been off the air and unmaintained for 16 years is almost certainly junk. Don't waste your time.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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Dale H. Cook
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Re: Reviving a dormant antenna system

Post by Dale H. Cook » Sat Feb 11, 2017 6:44 am

I will second Mark. Lack of pressurization for that many years is a killer. Yes, you could revive it, but you would have to invest so much money for labor and parts that you are better off scrapping it and replacing it with a new antenna and feedline system.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
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Jim Sofonia
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Re: Reviving a dormant antenna system

Post by Jim Sofonia » Tue Feb 14, 2017 1:48 pm

I agree that Mark is giving the best advice engineering wise. But money wise and who isn't these days why not pressure it up, load into it and see what happens. You won't waste that much time testing it, maybe will still work.

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Deep Thought
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Re: Reviving a dormant antenna system

Post by Deep Thought » Tue Feb 14, 2017 2:56 pm

It might work for awhile, but when (not if) it fails it will almost certainly cause other damage. If this station is so cash-strapped to not be able to do even this critical part right, maybe it should stay off the air.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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Dale H. Cook
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Re: Reviving a dormant antenna system

Post by Dale H. Cook » Tue Feb 14, 2017 3:33 pm

Again I will second Mark. This may be a case of "penny wise, pound foolish."
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ChuckG
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Re: Reviving a dormant antenna system

Post by ChuckG » Tue Feb 14, 2017 9:21 pm

Jim Sofonia wrote:
Tue Feb 14, 2017 1:48 pm
I agree that Mark is giving the best advice engineering wise. But money wise and who isn't these days why not pressure it up, load into it and see what happens. You won't waste that much time testing it, maybe will still work.
That is almost certainly what is going to happen.
The thinking (in general, I don't know the people involved here) seems to be, if it's replaced now the owner pays. If it burns up in 6 months, the insurance company does. That decision I'm sure has already been made.
Recommend it be replaced, in writing, with a copy in your own file... purge it as best you can, then cross your fingers and keep your local tower crew on speed dial.
<><><><><><><><><>
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Lee_Wheeler
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Re: Reviving a dormant antenna system

Post by Lee_Wheeler » Tue Feb 14, 2017 11:55 pm

Obviously different owners have different ideas and budgets. I would cover myself with all of the written caveats and then buy a reattach kit for the bottom connector and pull it apart to see how much water pours out. Assuming that you don't get a bunch of water out then you could reattach the connector and pick up a couple of large tanks of nitrogen and then have the top shorting stub cracked open and run a couple of tanks of nitrogen through it.

At that point you could seal it up and give it a go. The worst thing that would happen is that it blows up and they would need to replace everything as was originally suggested. The cost to try it is fairly minimal compared to the cost of a new antenna and a new transmission line.

If the station is planing on a huge marketing plan for a "Grand Opening" a failure comes at a very high cost but if you can put it on the air quietly to see if things hold for a week or so a failure isn't such a huge deal.

I did a real cheap installation where I was running a Harris 3.5 k into an old 3 " Heilax that we knew was bad since it had been abandoned for a dozen years. It leaked so badly that I actually drilled a hole in the low point of the loop so that the gallons of water could drain out and every year or so we would go through the draining process again. It is my understanding that they are finally, after 20 years or so of putting up with the leaks, going to replace the coax and move the antenna to the top of the tower. The new antenna was set at an elevation that matched the old center feed on a 10 bay antenna.

...Lee

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kkiddkkidd
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Re: Reviving a dormant antenna system

Post by kkiddkkidd » Wed Feb 15, 2017 7:46 am

Lee_Wheeler wrote:
Tue Feb 14, 2017 11:55 pm
If the station is planing on a huge marketing plan for a "Grand Opening" a failure comes at a very high cost but if you can put it on the air quietly to see if things hold for a week or so a failure isn't such a huge deal.
If money is that tight, make sure that the line is (and has been) dry and go for it. Giving it a good purge, sweep and pressure test would do a lot for my confidence if it were me waiting for the smoke and fire. If it makes it a couple of weeks or thru it's first SVR tstorm then I might start to relax a little. Absolutely make sure that the ownership is aware of the potential for it to burn out/down.

IF the line has been wet, won't hold pressure or you see anything other than a perfect sweep, I would absolutely nix it's reuse...

Honestly, it burning down in the middle of a marketing campaign would be my largest concern and have myself been bit by a stations premature upgrade party and huge marketing campaign. IE, the first time that a TX ran full power into a new antenna for more other than a couple of minutes of late night testing, the plate transformer melted down and the party sort of flopped...

The TX was a CCA FM10000 that was built during one of the times that CCA was folding up. CCA used 2ea 5h (IIRC) chokes in series in place of what should have been a single 10h (IIRC). It had been on the air as an A running about 4kw TPO for several years previous to an anticipated upgrade that required about 9kw. Peter Dahl told me that yes 5+5=10h but that the first 5h choke would saturate and start drawing current itself. We replaced the toasted xformer and the pair of chokes with a single 10h and the tx is still on the air to this day making full power. It made it's required TPO much, much easier after the filter choke swap.

Later,
--
Kevin C. Kidd CSRE/AMD
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AM Ground Systems Company
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KK Broadcast Engineering
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Deep Thought
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Re: Reviving a dormant antenna system

Post by Deep Thought » Wed Feb 15, 2017 2:35 pm

Joe Friday wrote:
Sat Feb 11, 2017 3:18 am
ERP is 28KW, TPO will be about 16KW.
Lee_Wheeler wrote:
Tue Feb 14, 2017 11:55 pm
The worst thing that would happen is that it blows up and they would need to replace everything as was originally suggested. The cost to try it is fairly minimal compared to the cost of a new antenna and a new transmission line.
If this were a low power scenario then I would not be nearly as apprehensive about just firing it up to see what happens. But a TPO of 16 KW into an un-maintained antenna and 3" Heliax is not going to just cause a little transmitter blip when it fails. If you get lucky it might only set the line on fire. If not, the transmitter may light up too (and given the obvious lack of proper funding here I would imagine this will be a POS transmitter feeding it).

Do what you want but make sure you have plate steel covering your butt. This is only one step away from "hey, hold my beer" -class shenanigans that most engineers would not get within two counties of.

Good luck.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

Joe Friday
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Re: Reviving a dormant antenna system

Post by Joe Friday » Fri Feb 17, 2017 6:17 pm

FYI...this is a non-comm religious station, and every dime that we have spent has been given as a donation to the project.

What I have done so far:

I have swept the antenna system with my TG/RLB, and get a return loss of 26 DB at the carrier frequency. Next I fired 200W into the system, and calculated the SWR at 1.08:1

Next, I did battle with an old 10KW CCA that had not been powered up in about a dozen years. I patched it into the system, and after overcoming some a couple of problems, delivered approximately 3500W into the system for approximately a hour. The system was stable, and showed approximately 25W reflected power. I took care of this station before it went silent 16 years ago, but don't recall how good the match was back then.

I have made no attempt yet to pressurize the system. I will do this soon.

Next, I am planning on having a climber go up and break the connection at the base of the antenna and see what things look like. I will also arrange for a megger and will test the transmission line while the connection is broken. I also plan to have him pull a couple of the arms off the antenna and have a look there as well.

If the connections look good, and the line passes the test with the megger, we will replace the gaskets and bolt things back up and see what happens at full power.

If the test with the megger fails, then it will be time to condemn the line.

They have a refurbished BE FM20B that we are waiting on an electrical contractor to complete a new service entrance and power distribution system to be able to fire up. There will be a Bird watcher as part of the transmission system once the buildout is complete. We also have a Dielectric coax switch to go in line to switch between the old CCA and the FM20B.

Money is available to replace the line, but if there is a chance the existing line could be usable, then they would like to keep the extra $$ as a reserve to operate the station once it gets on air. Monthly expenses will be north of $3K per month.

Please keep the ideas and opinions coming. Thanks to all who have taken time to share their thoughts.

Thanks,

Kevin

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Dale H. Cook
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Re: Reviving a dormant antenna system

Post by Dale H. Cook » Sat Feb 18, 2017 6:31 am

Joe Friday wrote:
Fri Feb 17, 2017 6:17 pm
I have made no attempt yet to pressurize the system.
That should have been the first step, before any electronic tests.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
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