Date: Tue, 31 May 2016 12:32:51 -0400
From: "john@kk9a.com" <john@kk9a.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Change in Frequency As Antenna Height Rises
Force12 sure has complicated way to assemble a standard 40m shorty beam!
I agree that is sounds strange that a dipole would shift 200+Khz moving it
from 30' to 60' however my quick EZNEC+ model shows an even bigger
frequency change when moving full sized wire dipole.
John KK9A
## The f12 240N, and 340N are assembled to the diagrams included. However,
they suggest to verify each individual ele for resonance at a specific freq.
Now most
folks just assemble per the instructions, and since everything is pre-drilled
etc, there
is nothing to adjust anyway...except for the linear loading. The linear
loading is not adjusted
either, and installed with max linear loading in each half of each ele. They
say that for each
6 inch adjustment of both tips, that resonance will shift exactly 100 khz.
The linear loading rods
on the N style els are made of solid 3/16 AL rod. Whats unique is they
extend outwards
towards the tips. The linear loading starts 7 ft 9 inches out from the
boom...so its not
half way out each side of the ele. Done that way so you dont require any
where near as much
loading.
## In my case, I replaced the solid LL rods with silver plated .375 inch OD
copper tubing.
Flattened on each end, so I can get a 1/4-20 bolt through each end....and then
right through
the AL tubing + solid fiberglass insulator. I need at least .375 inch
tubing...in order to handle a 1/4-20 bolt.
Q of each coil is sky high, like > 1750. ESR of each coil is just .07 ohm.
Each coil is 2.79 uh.
I worked the coils out on software such that I could re-use the oem solid
fiberglass insulators.
I can only wind a coil in full turn increments, so have to also juggle the
diameter and also the
spacing between turns to achieve the desired uh. Even then, I could easily be
off by a tiny bit.
So each ele has to be checked at a moderate height, like 35-40 ft, and tips
adjusted if required,
to resonate each ele at the desired freq.
## The 240N and 340N are already designed on software..and both work superb.
## I still contend that your EZNEC+ is out to lunch. Install a full sized
40m dipole at 30 ft.....
then move it up to 60 ft..... and keep the feedline the same length in both
cases. Resonance barely shifts
higher in freq. Ask anybody who has a motorized crank up tower + loaded
rotary dipole. Put the
test gear right at the DE, with a double male connector.
Jim VE7RF
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