Old feed point.
In early August of 2005, the SWR on the inverted L had suddenly
suspiciously high. The feedline and antenna seemed to be in good
last suspect was the inline capacitor. In late 2004, I had replaced
parallel mica capacitors with a single doorknob cap, and it had
the SWR to drift with temperature. Could it be that the cap was
and finally gave up the ghost?
Hole in the bottom.
Upon inspection of the inline cap (which had been housed in a 35mm
it became apparent that some four-legged creature had used the
canister as a
chew toy. A hole in the bottom/side allowed moisture to enter the
canister. Also, the doorknob capacitor was slightly crushed. A new
arrangement was needed. The new feed point had to be made so that
none of the
four-legged suspects could ever reach the capacitor or the
radiating element. It
also had to be made so that the radiating element could swing
around in the wind
without causing damage to the wire.
After two trips to the local hardware store (one trip is never
enough), all of
the necessary materials were gathered:
1- a three-foot length of 1-inch diameter PVC pipe 2- a plastic conduit box with a 1-inch opening at the
bottom 3- a two-foot length of flexible plastic tubing, with an
wide enough to snugly fit an insulated 12AWG wire through 4- a two-foot length of larger plastic tubing with an inner
just wide enough for a snug fit over the top of the ground rod 5- a miscellaneous plastic reducer; one end wide enough for
a snug fit
inside the upper hole of the conduit box, the reduced end small
to provide a snug fit for the flexible plastic tubing 6- a wide plastic washer, just big enough to cover the
inside the conduit box.
The two-foot length of plastic tubing was put over the top of the
and pushed down to the upper ground clamp. This covers the rough
the top of the ground rod. It also provides two other functions,
The three-foot section of PVC pipe was stood up on top of the upper
clamp. A mark was placed at a location 1-inch above the top of the
tubing and a hole was drilled at an upward angle at that mark. The
size of the
hole was just large enough for a snug fit of the smaller-diameter
The four-foot length of smaller diameter plastic tubing was cut in
piece was fit over a new length of 12AWG wire. That wire was then
within the 1" PVC pipe so that one end was sticking out the angled
while the other stuck out the opposite open end.
The smaller-diameter plastic tubing will then be a strain relief of
the end of the wire exiting the drilled hole. It will also, with
the air of
the larger plastic tube on the ground rod, protect the internal
abrasions, should the assembly swing around in the wind. The larger
tubing should also, theoretically, allow the PVC pipe to swing
on the ground rod.
The PVC pipe was placed over the top of the ground rod, so that the
hole was near the ground rod. The conduit box was fit onto the top
of the PVC
pile. The wire was threaded through the bottom hole, the plastic
over the wire and a loose knot tied in the wire, as a crude strain
The reducer was fit snug into the upper hole of the conduit box.
half of the smaller diameter plastic tubing was fit over the
wire, then into the hole of the reducer. This allowed for a tighter
fit of the
radiating element wire, as well as a semi-flexible strain relief. A
knot was tied in the radiating element wire, just inside the
as another crude strain relief.
Two eyelet terminals were soldered to the ends of the wires inside
box. A new doorknob cap was then bolted to the eyelets. The
cover of the conduit box was secured.
The wire sticking out the angled drilled hole, near the bottom of
the PVC pipe,
was soldered to the feedpoint wire at the ceramic egg insulator, as
it had been
previously. The four-legged creatures have not shown any signs of
these components, so leaving them as-is shouldn't be a problem.
The "new and improved" feedpoint. It allows the radiating element
around in the wind, while keeping it and the inline capacitor well
1.) In late November 2005, the SWR curve of the antenna was once
with the outside temperature. The doorknob capacitor was replaced
parallel 500pF mica capacitors, and the SWR-shifting problem went
2.) While the capacitor was being replaced, the inside of the
showed no signs of insect squatters.