[TowerTalk] Change in Frequency As Antenna Height Rises

[john at kk9a.com]

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 at contesting.com>
Subject:	[TowerTalk] Change in Frequency As Antenna Height Rises
From:	"Jim Thomson" <jim.thom at 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.