[AMRadio] "Hot" Broadcast Towers


Michael D. Harmon mharmon at att.net
Mon Jan 12 20:12:06 EST 2009


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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