Well, despite all the advice to the contrary, I installed my C-4C conversion
kit on my Force 12 C-3 today on top of the tower. Following
experience-based tips may help others who contemplate this.
1. Don't try it unless you are at least 6 feet tall. You don't have to be
strong (I'm not) but the long arms will be essential to adjusting the linear
loading. The spreader for the linear loading wires is set up so you can
slide it toward the mast, but you can only slide it about 6 inches before
you run into your mast (at least if the mast extends above the antenna).
2. In order to rope or bungee the element to the boom, you will need to
disconnect the linear loading wires on one side and tape them to the
element. This works fine, if you're six feet or more, because one tricky
part is feeding the disconnected linear loading wire through the far
spreader and clamping it down. Be very careful with over-working the linear
loading wires -- I had one break right where I bent it around the spreader
when I tried to strasighten it to pull it out of the spreader. The things
are expensive!
3. Expect that the element to boom mount will be tight on the boom -- you
may want to pry it a bit apart before you're 100 feet in the air (this _is_
experience talking).
4. The hardest part of the whole exercise is moving the boom in the
boom-to-mast mount so that the boom balances. It's hard to believe that the
antenna is designed so that the linear loading wires are actually above the
15-meter reflector, but it's so. The inside end of the linear-loading
spreader almost reaches the mast - but not quite.
5. Expect that the matching coil - 3 turns - may need to be spread apart
much further than the manual says to achieve a 1:1 or so to 1 match. Also,
I found that the linear loading wires needed to be shorted much closer to
the spreader than the instructions suggest, and that moving them a given
distance - say an inch - changed the resonant frequency less than the book
would suggest. However, when I got my body out of the near field, connected
the feedline, and checked the SWR, the minimum point was about 50 kHz lower
than when I was up alongside the boom with the Autek connected.
Well, we'll see how it works... I had been using a wide-angle inverted vee
with the apex at about 90 feet, and modeling doesn't show that much
improvement, at least in the IV's favored direction. Some intriguing
possibilities feeding it in phase with a flat inverted vee at about 50 feet
though. We'll see.
73, Pete Smith N4ZR
n4zr@contesting.com
... and not changing!
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