Speaking with my HAM hat on, to trim the tail dipole correctly you should
contact the local radio amateur club. Many of them will have VSWR meters
(which is wot you measure and optimise) and some will have them combined
with tunable signal generators. The kit is hand-held portable size so can
readily be brought to your site. The popular 2 meter band is only tens
of Mhz. above the airband, so these devices are easily set up for
optimising at mid-airband (taken as 120Mhz usually).
Interestingly it would not seem to be vital to use horizontal
polarisation for VOR -after all the dual Icoms still use the same "rubber
duck" (unless there is something devilish clever inside !) No doubt it's
not so effective that way, but I have never seen a comparison.
Polarisation tends to lost along low angle paths anyway for various
reasons and might even pick up a circular component, so there would not
even be a null plane when it reaches you.
gemin
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