|[AMRadio] Dealing with Ice on BC Antennas|
bguyger at yahoo.com
Mon Dec 16 23:03:30 EST 2013
We have two full class C FM's (100,000 W. ERP unlimited height -1600' in both cases) one on a broadband Panel Antenna that the heavy icing we just went through in Dallas didn't effect a bit. The other is on an ERI "Roto Tiller" antenna that can not have radomes because of wind loading. I had to back that one down to about 60% power for the duration. We also have a C2 FM (50,000 W. ERP at 500') also with a Roto Tiller that had to be backed down.
We also have 2 directional AM's that showed a drop in Common Point Resistance, from 50 ohms to about 47 ohms but kept right on going with slightly higher CP Current. Our Clear Channel AM (50,000 W. Non Directional) WBAP had no problem whatsoever.
On Monday, December 16, 2013 6:10 PM, Michael D. Harmon <mharmon at att.net> wrote:
Back in the Seventies, I worked as assistant chief at a 27 KW FM stereo
station in western Missouri. The antenna we used was a 5-bay
circularly-polarized unit fed with 3" hardline from a 10 KW
transmitter. The antenna was mounted on top of a 60-foot Rohn tower on
the roof of the Administration Building. We had fiberglass radomes
around the elements, but no deicers. Since we were in MO, we frequently
had freezing rain or other precip which would build up on the radomes,
and detune us. To get rid of the ice, we would retune the transmitter
and heat up the radomes. Pretty soon we would start hearing 'thumps' as
the ice started coming off, and then the power would shoot back up. We
would retune the TX back where it belonged, and everything would be
great till the next ice storm. We were fortunate that we were putting
out 10 KW with an RCA BTF-10E transmitter, which used a 4CX10,000D PA
tube. That big guy never even noticed the mismatch! I wouldn't want to
try that 'trick' with a TX using a tube operating way over its plate
dissipation rating, the way a lot of tube-type ham radio amps do.
Former First Phone holder - now General :(
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