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
To: <towertalk@contesting.com>
Subject: [TowerTalk] Change in Frequency As Antenna Height Rises
From: "Jim Thomson" <jim.thom@telus.net>
## heres the problem. f12 sez to check the resonance of each ele,
individually. IE: each of the 3 els has a center insulator. The
REF +
DIR normally have a shorting strap across their center insulators. The DE
normally has a helical hairpin
+ balun across it. When tweaking say the REF for resonance at 6900 khz,
the
shorting strap on the DIR is removed. The helical hairpin + balun is also
removed from the DE. Each ele is tweaked one at a time to whatever freq the
manual sez to use.
Then the shorting straps re-installed on REF + DIR. Hairpin + balun
re-installed on DE. A temp balun + MFJ used to tweak each ele
individually.
The F12 N style 40m eles are not full size. They range from 59 ft for the
REF...down
to aprx 52 ft for the DIR.
## If the 40m dipole alone shifts upwards 217 khz.... then how come it
doesnt shift 217 khz... when a motorized crank up is changed from 30 ft to
60 ft ?? It shifts very little.
A shortened 80m rotary dipole shifts very little from 40 ft to 100 ft.
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