Tiger Mountain (WA) master antenna catches on fire

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NECRAT
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Tiger Mountain (WA) master antenna catches on fire

Post by NECRAT » Sat Nov 10, 2018 10:39 am

http://sbe16.com/?p=6240

(Above article has pictures)
Jim Dalke, CPBE, Editor – Six Seattle Class C FM stations were knocked off the air Thursday morning, November 8 when a Tiger Mountain master antenna suffered major fire damage. Damage appeared to be confined to the antenna array on the tower and the transmitter buildings below were undamaged.
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Re: Tiger Mountain (WA) master antenna catches on fire

Post by kkiddkkidd » Sat Nov 10, 2018 11:17 am

Yikes... And I thought that a burned out 3in line was a PITA. I hope there isn't any structural damage on the tower.

How exactly would a panel antenna burn up most of the bays? Soot and debris thru pressurization plumbing or connecting coax links? No VSWR shutdown?

It just seems a bit odd that most of the bays look to be burned to some extent.

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Re: Tiger Mountain (WA) master antenna catches on fire

Post by Deep Thought » Sat Nov 10, 2018 2:54 pm

Looked to me like a radome fire...the top few seem intact. However they don't just go up on their own so something lower got damn hot.
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Re: Tiger Mountain (WA) master antenna catches on fire

Post by DaveSt » Sat Nov 10, 2018 3:15 pm

It is hard to imagine the failure mode that could have caused all that damage to every panel. It's a lot of RF and on 6 channels, so lots of volts too. Maybe a VSWR issue causing voltage breakdown at the antennas?

Some clear photos here: https://www.radioworld.com/news-and-bus ... ttle-radio

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Re: Tiger Mountain (WA) master antenna catches on fire

Post by kkiddkkidd » Sat Nov 10, 2018 4:38 pm

Deep Thought wrote:
Sat Nov 10, 2018 2:54 pm
Looked to me like a radome fire...the top few seem intact. However they don't just go up on their own so something lower got damn hot.
And since it looks like the damage wasn't isolated to 1 side, it was really, really damn hot or more than 1 bay lite off. Some of the pictures elsewhere look like chunks of bay elements that appear to be on the ground...

What a frigging mess...
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Re: Tiger Mountain (WA) master antenna catches on fire

Post by davek » Sat Nov 10, 2018 9:45 pm

kkiddkkidd wrote:
Sat Nov 10, 2018 11:17 am
No VSWR shutdown?
Depends on what type of combining system is in use. In a balanced combiner system the TX won't see any VSWR mismatch coming from the antenna.
I've always wondered why it's not common practice to monitor the VSWR of the combined output, where antenna faults can be detected and transmitters shut down if there is a major fault..

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Re: Tiger Mountain (WA) master antenna catches on fire

Post by DaveSt » Sun Nov 11, 2018 1:26 am

davek wrote:
Sat Nov 10, 2018 9:45 pm
kkiddkkidd wrote:
Sat Nov 10, 2018 11:17 am
No VSWR shutdown?
Depends on what type of combining system is in use. In a balanced combiner system the TX won't see any VSWR mismatch coming from the antenna.
I've always wondered why it's not common practice to monitor the VSWR of the combined output, where antenna faults can be detected and transmitters shut down if there is a major fault..
Yes the transmitters will see any reflected power on the combiner output. The reject loads are only there to absorb any power from mismatch in the two filters. Otherwise the reject load would need to be rated for the transmitter powers.

If the damage here was caused by arcing, the VSWR protection on the transmitters may not be fast enough to do anything about that until the antennas fail.

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Re: Tiger Mountain (WA) master antenna catches on fire

Post by Lee_Wheeler » Sun Nov 11, 2018 4:51 pm

Makes a case for a split feed to the panels. Most master antenna systems I've been involved with have a line to the top half and a line to the bottom half that can isolated in case of a failure.

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Re: Tiger Mountain (WA) master antenna catches on fire

Post by DaveSt » Mon Nov 12, 2018 12:47 am

Lee_Wheeler wrote:
Sun Nov 11, 2018 4:51 pm
Makes a case for a split feed to the panels. Most master antenna systems I've been involved with have a line to the top half and a line to the bottom half that can isolated in case of a failure.

...Lee
The photos do show a dual feeder arrangement for this system. With the amount of damage that would not help here though. I do wonder if they were feeding full power into the lower half of the system, that could well exceed the rating of the panels with 6 services.

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Re: Tiger Mountain (WA) master antenna catches on fire

Post by NECRAT » Tue Nov 13, 2018 8:56 am

Instead of speculating, we could also just wait for the report to come out as to the cause.
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