[AMRadio] "Hot" Broadcast Towers


Stevan A. White w5saw at pathwayz.com
Mon Jan 12 20:58:17 EST 2009


Well Mike, OSHA says it's against the rules to climb a hot tower these 
days.  It's the suits with their wingtip$ you know, who have no idea 
what's what.

I am all too aware of what's it's like to be the only guy on site 
working on a transmitter.  Even if it's just changing a tube, you want 
to err on the side of caution, nothing else.  I've been startled by the 
dehydrator just like you have but I have my own "gotcha" I'll never 
forget.  At one site where I used to be chief engineer I was often 
greeted by wasps when I entered the building, not one or two but 
sometimes twenty or thirty.  A rather large bug zapper appeared one day 
and the majority of the welcoming committee lay on the floor beneath 
"the apparatus."  I got a late night call to go work on the transmitter 
because we'd taken a lightning hit and it didn't want to play at full 
power.  I had removed about 147 screws to get to the bowels of the 
transmitter to replace the failed component.  The smoke had gotten out 
and there lingered in the air the pungent reminder of excess power going 
where it shouldn't.  I was slowly and carefully performing the task at 
hand when a rather obese horsefly, mesmerized by the pretty blue glow, 
flew right into "the apparatus."  It sounded just like a wirewound 
resistor getting chewed up by high voltage.  I didn't do any damage to 
my shorts but I later had to repaint the room because the closest wall 
and the ceiling above the transmitter turned blue and then the paint 
started to peel after I vocalized my shock and surprise.

73 de W5SAW, Steve White

Michael D. Harmon wrote:
> As a former broadcast engineer (MANY years ago), the discussions of hot 
> towers, lighting transformers and base insulators caught my attention.  
> One issue some of you may not have thought of is tower/antenna 
> maintenance.  Many AM stations never go off the air.  Some of them run 
> directional at night to avoid interference with other stations, and a 
> lot more simply have a "night power" restriction, but the tower is fed 
> with RF 24/7.
>
> You might ask how a worker can climb a tower while it's hot.  Well, 
> think about the birds perching on the 12,000 volt lines which run 
> overhead through the community.  If they are on the wire, they're at 12 
> kV potential, and don't even know it.  On the other hand, I've seen 
> entire sections of town blacked out because a hapless squirrel or 
> raccoon tried to climb a pole with a "pole pig" (distribution 
> transformer) mounted on it, and managed to get between the hot wire and 
> ground.
>
> The answer is - they jump.  They stand on the ground next to the tower 
> base, give a giant leap and grab hold of the tower.  Same way with 
> getting off.  Climb to the bottom, make sure all your belts, etc are 
> completely loose, and give a giant spring backwards.
>
> I spent my time back in the early Seventies signing logs, trying to 
> de-ice the elements after a winter storm, and getting late-night calls 
> from a so called "audiophile" board operator who swore that the 
> equalization had magically gotten out of whack (since he had come on 
> duty) on the old Ampex AG-350 tape decks in the control room.  Yes, I 
> was one of those First Phone holders who were downgraded to the 
> so-called "General Radiotelephone" license a few years later.  I 
> remember one cold blustery winter night when I got a call from the board 
> man that the transmitter wasn't making power.  I went in, and found  a 
> 4CX250B driver tube in our RCA BTF-10E FM transmitter that was getting 
> VERY soft.  After signoff (1:00 AM), I shut down the transmitter and 
> went to work.  The transmitter room was as quiet as a tomb after the 
> blowers all shut off, and it was eerie having the station to myself.  
> The plate supply in the transmitter was around 6,500 volts at about 2.5 
> amps, and I was painfully aware that I was the only guy there, so the 
> need for caution was at the forefront of my mind.   The driver tube was 
> all the way in the back, under a shelf beneath the 4CX10,000D PA, and 
> required an offset screwdriver to get the anode clamp loose.  I opened 
> the doors, hit everything with the grounding stick, and reached in and 
> started loosening the plate clamp on the driver.  I grabbed the tube, 
> and was pulling it out of its socket when the old Andrew dehydrator 
> about 2 feet behind the transmitter decided to kick on. "Karoom, CHUG, 
> CHUG, CHUG ..."
>
> I swear it couldn't have scared me more if it had been a quarter stick 
> of dynamite.  I peeled the skin from my wrist all the way to my shoulder 
> getting my arm out of that transmitter!  I don't know how, but I never 
> dropped the tube!  After recovering from my shock (and changing my 
> underwear), I put the new tube in, checked the driver and PA tuning and 
> went home.  It's been 35 years since that incident, but I still remember 
> it like it was yesterday.
>
> I don't know if the technique for mounting and dismounting hot towers is 
> still the same or not.  With all the OSHA rules and concern over 
> workplace safety, I'd be very surprised if there weren't some 
> politically correct way to do it nowadays, but that's the way we did it 
> in the Sixties and Seventies.
>
> Hope I didn't bore you with my story!
>
> 73,
> Mike Harmon, WB0LDJ
> mharmon at att dot net
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