[TowerTalk] Change in Frequency As Antenna Height Rises

[Pete]

There is a better way for at least some  F12 40m yagis. My EF240S has two identical linear loaded dipoles, and I had tried the part-height tuning without success   Finally, 
I put it up at full height and put a signal source some 


from my iPhone3

> On May 31, 2016, at 12:32 PM, "john at kk9a.com" <john at kk9a.com> wrote:
> 
> 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.
> 
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