I may have posted this in the past, but it's fitting for the
recent discussion about feeders ....
I made two 1/4" brass rods to bring my feeders through the
wall of the shack with 2" (hollow) porcelain cones on both
sides of the wall. The wall is of the usual construction with
2x4" studs and foil-backed fiberglass insulation. The outside
wall is plywood with cedar shingles.
I drilled 1/4" holes through the wall to pass the rods, never
giving a thought to the aluminum foil on the insulation. The
installation worked well for many years, but I began to see
signs of a possible intermittent connection in the feeder/antenna
system. The antenna is an 80M 1/2 wave zepp that's up 65'
and can be raised/lowered by ropes. After several attempts
to find something loose and pondering the issue, it dawned
on me that the foil might be coming in contact with one of
the feed-thru rods.
I removed both rods from the wall and was astonished to find
that one of them showed signs of arcing and heat discoloration.
( I had ran a KW in the past.) From the location of the arcing
marks and the discoloration it was obvious that RF had been
flashing over to the foil!
The "fix" was to drill larger holes (1/2") and slip 1/4" ID, 1/16"
wall Tygon tubing over the rods that was long enough to extend
into the hollow portion of the cones.
BTW, I use a pair of "serious" high-inductance RF chokes from
each side of the feeder to the station's ground system. (2" copper
strap, 17 ground rods, literally thousands of feet of copper
counterpoise/radials. I've had one lightning hit in 30+ years. There
are four towers on the property in the 75' to 100' range, but the
hit came into the house on the phone line. Killed all the phones
except the "real" Ma Bell's, all the computer modems and a range
hood's speed control.
73! Ken Kopp - K0PP
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