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@kk9a.com" <john@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@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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