[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 
> 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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