|[AMRadio] "Hot" Broadcast Towers|
robertcharles at att.net
robertcharles at att.net
Mon Jan 12 20:35:47 EST 2009
Many Thanks Mike, for sharing your knowledge and experience with us. This is about as exciting as when I first received my Novice back in the mid 60's. And I could only find out these things off the AM web page and its gracious readers.
-------------- Original message from "Michael D. Harmon" <mharmon at att.net>: --------------
> 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
> 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!
> Mike Harmon, WB0LDJ
> mharmon at att dot net
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