Visual "clipping"?

[Arny Krueger]

Actually, no, it's the last couple of inches.

Yeah, in this case something about really coarse crushed coral, recently
excavated from just any part of Florida south of Ft. Lauderdale.

I doubt that many people ever died of falling. They
pretty much all died of the sudden stop at the end.

Well, they say a few hearts stop in anticipation... :-(

Suggesting ... ?

That I was reaching for the safety switch, which I seem to recall was at the
base of the radar antenna. Between a little slip on a wet work platform
that had been recently doused with hydraulic fluid and the fact that the
radar was controlled remotely until I flicked the switch...

IOW, as those bumper stickers go: Stuff happens.

 

[Jerry Avins]

Michael A. Terrell wrote:

...

How do you propose to control what flows into the waveguide? I have
never heard of anyone even attempting to repair high power waveguide in
the field. Also, since it is pressurized, what is to stop you from
making the crack worse?

The same surface tension that draws the braze into the crack tends to
keep it there unless the inside surface has been fluxed. It worked on a
small guide, and inspection showed that the inside surface was
undamaged. As for pressure, you release it. I didn't imagine that the
waveguide would be repaired while in service. You have to shut down the
station to replace the guide, no?

Are YOU willing to make repairs over 1000 feet in the air, while
hanging from a harness? There are some pretty nasty winds at that
level, so close to the ocean. Some people don't try to get by with half
assed repairs. This is a straight vertical run, other than the
flanges. As I stated earlier, the waveguide was under warranty and the
tower lease included all required repairs. IOW, WE were not allowed to
even attempt a repair, even though the tower was on the TV station's
property.

I wouldn't be willing to unbolt the choke joints at that height today,
but 50 years ago I might have. There's little difference between using a
torch and a wrench. Both are two-handed operations.

Please note that I didn't suggest that you ought to have brazed it, or
even that brazing would work. Since it was some other's responsibility,
you did well to leave it for them. Another question: How did your
colleague come to be leaning against the cracked portion?

Jerry

 

[neon]

Clipping on digital is worst like what? one rail to the other rail? if there is overdrive it is only device storage to consider.

 

[[email protected]]

You and I couldn't, but an engineer/technician working for a
company such as GE, Westinghouse, Philips or Osram might go mad and
try something like that. If we suffered that same fate we might try
applying 240V A.C. to a 2.6v PR2 bulb to see "what would happen".

Ah, the EtherKiller...
http://www.fiftythree.org/etherkiller/img/etherkiller.jpg

 

[Michael A. Terrell]

Michael A. Terrell wrote:

...


The same surface tension that draws the braze into the crack tends to
keep it there unless the inside surface has been fluxed. It worked on a
small guide, and inspection showed that the inside surface was
undamaged. As for pressure, you release it. I didn't imagine that the
waveguide would be repaired while in service. You have to shut down the
station to replace the guide, no?

They had trouble replacing it during the weekly downtime from
midnight to 6 AM monday morning. If they are going to remove it, haul
it to the ground, repair it, haul it back up the tower and reinstall it,
they might as well replace it. It would have added at least 2 hours
just to haul the thing up and down the tower in the freight elevator,
plus the time on the ground to repair it. I wouldn't accept any brazing
done without flux or dressing down the repairs, both inside and outside
of the waveguide. No half assed work is acceptable when you need a full
six MHz at 15 KW of UHF.

It is my understanding that they had the new waveguide up the tower
and waiting for sign off. They depressurised the waveguide by removing
the bad section. Then the two were pieces were swapped, and the new part
bolted into place. It takes time to pressurize almost 2000 feet of large
rectangular waveguide without damage, then you have to make sure it is
at the proper PSI before the transmitter goes back on line. Downtime is
damn expensive in broadcasting, so you try to do things only once, and
right. I could see a small fly by night, shoestring station attempting
a half ass repair, but this plant was running 5 MW EIRP. A proper
repair meant it would be reliable. There is nothing more frustrating
than running around putting out fires, rather than doing scheduled PM to
prevent those problems. For instance. I lost the same power supply
board in all three studio cameras within 48 hours, during a 12 day
telethon. Luckily, I had just rebuilt the spare board from an older,
but similar RCA camera, and they were interchangeable. By the time I
finished, I had used a couple hundred dollars worth of electrolytics. I
was slipping into the studio, and repairing cameras between shots for
three days. Normally, they were only used two ours a day for live work,
plus whatever studio time was sold. While in use, the cooling fans had
to be shut off, or you could hear them on air. That let the internal
temperature go up about 20 degrees, which killed any weak components.

I wouldn't be willing to unbolt the choke joints at that height today,
but 50 years ago I might have. There's little difference between using a
torch and a wrench. Both are two-handed operations.

Please note that I didn't suggest that you ought to have brazed it, or
even that brazing would work. Since it was some other's responsibility,
you did well to leave it for them. Another question: How did your
colleague come to be leaning against the cracked portion?

He wasn't a colleague, he was an employee of the tower company. He,
and five others were doing their annual inspection for loose and cracked
bolts, peeling paint, and any other defects. He was about to wedge
himself between the tower and waveguide to check some bolts, when he
felt the heat and pain.

That tower cost over a million dollars to erect, and had seven
broadcast transmitters, and numerous government agencies as clients.
The TV station owns the land, and transmitter building. They leased the
land for the tower to the tower company, and the tower company leased
them space on the tower for the same amount, per month. The tower
company had tried to buy the site, but the owner wouldn't sell. When he
died of old age about six months later, his will had a set price to
offer it to the Christian TV station. If they didn't buy it, then it
was to be sold for whatever it would bring. The cost to do a major
repair, or even worse, to have to replace that tower would be at least
double or triple. It is a little over 20 years old, and with proper
care and no hurricane damage should last at least another 30 years.
There are some 80 year old towers still in use today. The WSM AM tower
is one of them, along with the WLW AM tower.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

I always liked the time I spent in a climbing harness attached to something
firm. It was the unclipping to take up some new position or the time that
had to be spent high unclipped that bothered me.

I've never worked on towers higher than about 80 feet, but as they say, its
the first 40 feet that kills you. :-(

In fact a tech at another battery in our batallion did fall off a tower
during my tour in Fla. and suffered the expected fate. :-(

The worst thing that ever happened to me was a mild head injury due loosing
my balance and ending up too close to a slewing radar. Towers in Homestead
were covered with about an inch of water due to condensation from the
everglades and the ocean, in the morning. I was approaching the safety
switch at the time!

There were multiple key lock interlocks on the RADAR at Ft Rucker,
too. Any one was enough to shut the system down, and the keys could
only be removed in the 'SAFE' position. I did a little work on some of
the older RADAR, but they had a full time staff for those two systems.

The anecdote reveals the context with the mention of X-band. It was likely a
military radar, and the brazing was probably done with the piece of
waveguide removed from the radar and sitting on a bench.

I would have to have it X-ray inspected before I would put it back
into service. I saw enough burnt waveguide in the trash at Ft Rucker.

Have you ever used waveguide big enough for a small person to crawl
through? This was the largest waveguide I've ever worked with.

The part about the story that I don't get is that we had ionization
detectors on our waveguides, and they always seemed to shut things down
before the situation got too far out of hand.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Jerry Avins]

They had trouble replacing it during the weekly downtime from
midnight to 6 AM monday morning. If they are going to remove it, haul
it to the ground, repair it, haul it back up the tower and reinstall it,
they might as well replace it. It would have added at least 2 hours
just to haul the thing up and down the tower in the freight elevator,
plus the time on the ground to repair it. I wouldn't accept any brazing
done without flux or dressing down the repairs, both inside and outside
of the waveguide. No half assed work is acceptable when you need a full
six MHz at 15 KW of UHF.

[snip interesting description of the work]

One doesn't ordinarily* braze well without flux. For a crack in a
thickish flat surface, I make a half-thickness groove along the crack,
apply anti-flux (India ink or a slurry of ocher or rouge) along the edge
of the groove, and flux within it. (For brass, I usually use EasyFlow or
a 36% silver braze so that melting the base isn't a concern. Ordinary
brazing rod works /with most brasses/ with enough care.) Dissection has
shown that the braze penetrates the crack most of the way through. The
annealing due from making the joint and the slight dome of brazing
material makes the joint more immune to subsequent cracking than the
rest of the material.

A good braze isn't half-assed. How are the waveguide's flanges attached?

Jerry
________________________
* With typical rod, mild steel brazes readily without flux in the heat
of an oxyacetylene torch adjusted to a mildly reducing flame.

 

[Michael A. Terrell]

One doesn't ordinarily* braze well without flux. For a crack in a
thickish flat surface, I make a half-thickness groove along the crack,
apply anti-flux (India ink or a slurry of ocher or rouge) along the edge
of the groove, and flux within it. (For brass, I usually use EasyFlow or
a 36% silver braze so that melting the base isn't a concern. Ordinary
brazing rod works /with most brasses/ with enough care.) Dissection has
shown that the braze penetrates the crack most of the way through. The
annealing due from making the joint and the slight dome of brazing
material makes the joint more immune to subsequent cracking than the
rest of the material.

A good braze isn't half-assed. How are the waveguide's flanges attached?

It depends on the manufacturer, and the application. Some are brazed
to the outside, while others are soldered. A flat plate is milled to a
couple thousandths larger than the OD of the waveguide, a groove for the
gasket is machined into one side, and it is put into a fixture for
proper alignment. Then the two are joined. The flanges are not
intended to support much weight, they are intended to make air and RF
tight connections.

BTW, the crack was in the outside corner, where two beveled brass
corners are aligned and machine brazed, then ground down and polished.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida