How Old is Old?

FM does it with frequency!
Lee_Wheeler
Posts: 70
Joined: Sun Jul 24, 2016 1:53 pm
Location: Kansas City

How Old is Old?

Post by Lee_Wheeler » Tue Jan 17, 2017 10:04 pm

This is odd, I have actively been in this business since 1983 and I have done hundreds of upgrades and new station builds but I am facing a situation that I really don't have experience with.

All four of the stations that I am taking care of day to day are Docket 80-90 Class C builds (the "upgrades" that were forced to keep the full Class C status on the license) that were done between 1985 and 1987. Those buildouts were monstrously expensive and many of the decisions that surrounded the facilities were not made based on the soundest logic but were instead done to achieve the magical 300 m HAAT. As a result three of the four stations are running twin 25kW transmitters combined into 5 or 6 bay antennas and TPOs between 42 and 45 kW. In all cases the transmitters are 1986 models or older, the Continentals are actually 1980 builds.

A little over a week ago I had the 4" rigid at one of the stations blow up and we are presently on a backup antenna at about 300 ft. The big burnout was at 880' AGL with another minor burnout at around 450'. The line is all full of trash and it will need to come down to get cleaned and basically renwed. I have ordered the parts and pieces to basically rebuild the line and replace the Teflon wafers at the top of each section as well as all new watchband springs and a gob of spacing pegs. It will all need to come to the ground to get swabbed out with alcohol and the "bullets" renewed. This line is SWR K-Line so it doesn't really use bullets per se, they are actually made into the sections.

What has me concerned now is that antenna in particular and really all of the antennas. One of the stations apparently had the antenna blow up about 10 years ago and it was rebuilt at that time, another of the stations has had the same antenna up since the summer of 1985 and it has never been touched, and the antenna above the burned out line was new in 1986. The 1986 model has had an occasional loop replaced when either it just fell off, as it did once, or when a deicer element burned out but I don't have any clean records of what bay numbers were worked on and when since all of the logs got thrown away in a big housecleaning.

My suggestion to the owners was to get new bullets, O-Rings, and hardware and drop that antenna to the ground for a rebuild while we have the tower rigged to deal with the burnout. ERI can provide the parts and it isn't a ton of money but it isn't insignificant either. ERI seems to think that we are throwing good money after bad trying to rebuild it and that the antenna should just be replaced with a new one after being on the tower for 30 years.

As I think back on the original builds it seemed like we were replacing really old antennas at the time of the upgrades but in reality they weren't that old - maybe 15 years old at the time. The original facilities were built when FM was just getting hot in the early to mid '70s.

What have your experiences been with old antennas? My gut says that I should be able to replace the bullets and O-Rings, clean everything real well, and they should be good to go for another 20 years but I hate to just waste money if they indeed totally and irredeemably fall apart after that length of time. Add to the equation that this is pole mounted at the tip top of the tower so it is the one that gets hammered the most by lightning. These are not the real old style rototillers that had the miter cut loops and the notorious leaking problems around the insulators, they have the flanges at the insulators and the loops are the bent style.


...Lee

User avatar
Deep Thought
Posts: 3150
Joined: Thu Mar 20, 2008 9:23 am
Location: La Grange, IL
Contact:

Re: How Old is Old?

Post by Deep Thought » Tue Jan 17, 2017 10:39 pm

It all depends on the environment and operating history.

If you have not had any "events" like severe icing, major lightning strikes, unexplained VSWR jumps or pressure leaks then 30 years isn't that old, but you're probably a sitting duck for something to happen if there has been no maintenance on the subject antenna over that time. At this point it doesn't owe you anything nor you it. Anything at ~1000 feet is taking some serious abuse. At the least I would bring it down just to take a look at it if this hasn't been done.

ERI is trying to sell antennas. While there is some validity to their suggestion there is nothing that is inherently a wear part in an antenna except for the bits that are subject to mechanical stress. You're already looking to replace those and do a good mechanical inspection of the bays. You are not going to get any sort of major jump to new technology with a new antenna, and will instead just get a younger copy of what you already have.

But in the end, the budget will control what you do.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

Joe Friday
Posts: 65
Joined: Tue Dec 16, 2014 3:47 am

Re: How Old is Old?

Post by Joe Friday » Wed Jan 18, 2017 6:25 am

I take care of a class B that had a burn out of their HJ8 line about six years ago, before I started taking care of it. They considered a new antenna at the time, but the lead time was an issue. The antenna in an early six bay ERI rototiller, was installed in the early 70's. ERI was able to supply a rebuild kit that worked perfectly. The antenna was brought down, refurbished and reinstalled. Six years later it is still working perfectly without any issues, without any leaks. The antenna is a little more sensitive to ice than the other newer ERI antennas, but it has continued to work well following the rebuild.

As always, YMMV. God luck!

Kevin

Kelly
Posts: 476
Joined: Thu Aug 21, 2008 5:32 pm
Location: Washington D.C. Area

Re: How Old is Old?

Post by Kelly » Wed Jan 18, 2017 9:06 am

A couple thoughts: Assuming your existing transmission line is made up of 20' sections of 3 1/8" hard line, it is conceivable that over time bullets develop resistance and fail (especially the watch spring kind), O-rings can leak, causing moisture to get into the line and cause flash-overs. That said, if the flash-over or bullet failure was bad enough to cause catastrophic line failure, then I'd see if the VSWR protection is working on the transmitter, or whether somewhere down the line (pardon the pun), your predecessor disabled it.

Honestly? Anymore I'd say you may want to consider going to flexible line like Heliax. Far less joints to fail, get water into, rebuild and, as an added bonus, less transmission system group delay by eliminating all those bullets.
Skype:kellyalford Twitter: @KellyAlford

User avatar
Jim Sofonia
Posts: 120
Joined: Fri Jan 30, 2015 11:15 pm

Re: How Old is Old?

Post by Jim Sofonia » Wed Jan 18, 2017 11:57 am

I'd agree with Kelly and replace the rigid line with heliax. Your tower crew is going to cost plenty no mater if they re-hang old line or new. In fact new line would be less crew time as they don't have to bolt all those sections together. 35 years ago when I started in this business they were build a completely new 100kw facility except for old rigid line that came off an old tv tower. They scrubbed and cleaned all the sections and put in all new bullets and O-rings, but it burned out twice about every two years. We sent up heliax and never had a problem since. I'd change out the 32 year old antenna too. Just tell management what you want and let them figure out how to pay for it.
You can recover some of the cost when you scrap out the old line. That red copper brings a nice salvage price.

taylorengineer
Posts: 26
Joined: Fri Jun 10, 2016 12:43 pm

Re: How Old is Old?

Post by taylorengineer » Wed Jan 18, 2017 1:53 pm

Lee: I'm also trying to decide on replacing, or refurbishing a 30 year old ERI 10 bay rototiller. I have never had a single antenna problem in my 22 years at the station but the site became standby a couple of years back and I worry about reliability. It's a bad day when both your sites refuse to play radio!
You can make the argument to go either way. In my case, it is almost as cheap to replace the antenna as to rebuild. (Replace with a 6 bay and higher TPO. Does not account for increased operational costs)

rich wood
Posts: 88
Joined: Mon Jan 24, 2011 10:56 am
Location: Madison, WI
Contact:

Re: How Old is Old?

Post by rich wood » Thu Jan 19, 2017 9:03 am

Wear and tear on the bullets in a 35 year old antenna should be replaced. ERI recommends rebuilds every 20 or so years. This does depend on the structure. If the antenna is side mounted on a guyed towed there is less sway. If the antenna is on a mast, there is a lot more sway and rebuilding is important. As was said, at this point the antenna is fully depreciated, so depending on the amortization schedule the station has for cap X projects determines rebuild or replace. I have found that antennas tend to degrade in coverage over time and it is like a frog in a slow boil, no one really notices the difference until it burns up. Replacement will more than likely give you more punch in the field strength. Any rebuild or replacement should be field tuneded to get the VSWR notch in the right spot for year round operation. VSWR above 1.09:1 can cause loss of separation in the audio also.
As far as the rigid line, once the burning starts you need to be very aggressive on the rebuild. There are many crews out there, but I have found Precision Communications to be the best on line rebuilds. They can do it in the air and are really fast at it.
http://pcitower.com/
Also, after the rebuild, it is imperative to sweep test the system with an analyzer of good quality and check the voltage handling capacity of the line with a hi-pot tester. 4" line should be good for at least 23kV. This will ensure the viability of the line for the long term. Flex lines, once the burning starts are really a throw away product. The "cut back till it looks clean" works sort of, and if you like to get regular sleep it is not the best option.

Lee_Wheeler
Posts: 70
Joined: Sun Jul 24, 2016 1:53 pm
Location: Kansas City

Re: How Old is Old?

Post by Lee_Wheeler » Thu Jan 19, 2017 9:33 pm

Other than getting the parts on order to rebuild the line the people that write the checks have it all in their hands now. As far as the antenna goes it seems that the options range from doing nothing to replacing but I don't know what they will do. My gut tells me they are trying to find a new antenna at a Nicom price. Whatever they want me to do, I'll do it. If it all blows up again then I'll deal with that too.

Interesting that PCI got brought up. I had them in to do the initial damage assessment and Jackie has me penciled in for a crew once the coax parts get in. If the folks that write the checks want to rebuild the existing antenna I need to get some measurements first so that ERI can send in the correct parts but they can do that while they are rigging the tower. It sounds like ERI can get what I need out the door same day which is something I've always liked about ERI. I torched a 10 bay 25 years ago and they had 4 new bays flown into the airport same day.

I have used PCI on several jobs now and I always get a competent crew. I used to have a top notch crew right in town and never even had to think about it but a cable broke and we lost him. Most of the towers I am on are American Tower properties so I have to work off of their approved climber list and fortunately Precision Communications is on the list.

...Lee

Lee_Wheeler
Posts: 70
Joined: Sun Jul 24, 2016 1:53 pm
Location: Kansas City

Re: How Old is Old?

Post by Lee_Wheeler » Wed Feb 08, 2017 8:56 pm

After a few fits, starts, and weather delays the crew finally got to the lower burnout at 450'. For the benefit of those who have never had a rigid coax burnout here are a couple of pictures. I could actually see through this burnout with the TDR to the second one at 850'. The top burnout must be much worse because I couldn't see anything past it.
Inner at 450 ft - 1.jpg
Inner at 450 ft - 2.jpg
This is SWR K-Line that has the bullets built into the inner conductor.

...Lee

rich wood
Posts: 88
Joined: Mon Jan 24, 2011 10:56 am
Location: Madison, WI
Contact:

Re: How Old is Old?

Post by rich wood » Fri Feb 10, 2017 2:39 am

Lee,
Winter burn outs are the hardest to fix due to the weather delays and the short work time in the cold. That like section looks like the watch band spring let go. How does the rest of the line look in a wide (350 - 700 MHz) Time Domain pulse?

Lee_Wheeler
Posts: 70
Joined: Sun Jul 24, 2016 1:53 pm
Location: Kansas City

Re: How Old is Old?

Post by Lee_Wheeler » Fri Feb 10, 2017 5:08 pm

That was the lower burnout that I could actually see through with the TDR. The top burnout burned the line completely in half and I can't see anything past it. We are dropping out everything below the top burnout and then a section or two above to see how it looks. The line is all being reconditioned with new watchband springs, new spacing pegs, new teflon retainers, and everything gets the Scotchbrite and alcohol treatment. Once it goes back up I will get a better look at it with the network analyzer and the TDR but in theory it should look flawless. I bought enough watchband springs to replace all of them above the top burnout and if that line is clean hopefully they can replace those without dropping out the line.

They are real close to the top burnout, about 3 sections away, but it was too windy today to work at altitude. Hopefully we get the rest of it to the ground tomorrow.

I found another 5 watchband springs so far that were moments away from going, a couple of them came out in pieces. Here has been my life for the last week:
Section below the burnout.jpg
Inner conductor being cleaned.jpg
...Lee

User avatar
kkiddkkidd
Posts: 468
Joined: Mon Dec 03, 2007 11:13 am
Location: Lawrenceburg, TN

Re: How Old is Old?

Post by kkiddkkidd » Fri Feb 10, 2017 5:31 pm

Lee_Wheeler wrote:
Fri Feb 10, 2017 5:08 pm
I found another 5 watchband springs so far that were moments away from going, a couple of them came out in pieces. Here has been my life for the last week:
...Lee
What is this "watchband spring" that you speak of?
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

Lee_Wheeler
Posts: 70
Joined: Sun Jul 24, 2016 1:53 pm
Location: Kansas City

Re: How Old is Old?

Post by Lee_Wheeler » Fri Feb 10, 2017 6:59 pm

The line is the SWR K-Line that really doesn't use bullets. I lifted this from the SWR homepage that kinda shows how the system works.
kline2.gif
The watchband spring is under the teflon cap.

...Lee

User avatar
Deep Thought
Posts: 3150
Joined: Thu Mar 20, 2008 9:23 am
Location: La Grange, IL
Contact:

Re: How Old is Old?

Post by Deep Thought » Fri Feb 10, 2017 11:44 pm

kkiddkkidd wrote:
Fri Feb 10, 2017 5:31 pm
Lee_Wheeler wrote:
Fri Feb 10, 2017 5:08 pm
I found another 5 watchband springs so far that were moments away from going, a couple of them came out in pieces. Here has been my life for the last week:
...Lee
What is this "watchband spring" that you speak of?
They are also used in most Heliax-type connectors on the outer conductor, which should give you an idea of what they are like.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

User avatar
kkiddkkidd
Posts: 468
Joined: Mon Dec 03, 2007 11:13 am
Location: Lawrenceburg, TN

Re: How Old is Old?

Post by kkiddkkidd » Sat Feb 11, 2017 7:42 am

I get it now... I was thinking of a concentric WATCH spring not a watchband and trying to figure out where that fit.

I found some old bullets at a site that had something similar inside the contact to provide outward pressure.

Thanks for the clarification.
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest