At 09:11 AM 7/16/99 -1000, Jim Reid wrote:
>
>John asked:
>
>> Yet no one has told a bad story or cautioned us about
>>using the Force 12 yagis QRO at heavy duty
>>cycles - right??...... I asked about this once before,
>>and the responses were 100% in agreement that the
>>Force 12 yagis could take power and heavy duty cycle.)
>> I'd like to know if others would worry about this.
>
>So what happens to your operation once the bead
>balun gets hot and experiences the "big bang" ?
>
>Does your vswr go up? Does the antenna efficiency
>become lousy? Maybe the driven element is no
>longer balanced? How do you know down in the
>shack that the balun is now NG?
Interesting question -- I took what was probably a lightning discharge on
the uncased bead balun on my 40-meter antenna, and didn't suspect it until
I took it down for other reasons. With Teflon coax you might well power
the beads and never know it (I doubt it's really that much of a bang - more
likely the beads just temperature-cycle until they fracture).
Incidentally, the reason I don't think I had a heating failure is that I
understand these will happen on the end of the bead balun nearest the
antenna, and my blowout was in the middle of a 50-bead string- two beads
gone completely, a big hole in the tape wrap, a gouge in the teflon coax
outer jacket, some braid visible, and 3-4 beads on either side cracked but
still contained within the tape.
73, Pete Smith N4ZR
n4zr@contesting.com
Sometimes a tower is just a tower
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