All antenna designs are compromises of one thing vs. another. A
straight dipole isn't 50 ohms; Archer's antenna appears to of the type
that solves the balun problem; 1.1:1 VSWR at mid-band is nice, but if
you need performance at 118.5 like our nearby control tower, you need
broadband. Anyway, here's yet another version with copper tape, with
claimed broadband performance and natural 50 ohms impedance:
http://www.express-aircraft.com/antenna_design.htm
It comes out shorter that a straight dipole. Needs the ferrite beads,
though. Be cautious about user reports w/o the details of what metal
is or is not nearby. I have an MFJ antenna analyzer, and it's been
educational to suspend different designs well above the ground and see
what happens on the MFJ when things mimicking wiring or control system
items are introduced within 2-3 feet of the tips. I tested a friend's
Archer antenna setup, the one that's supposed to work in a fiberglass
fairing on a metal airplane. Disaster -- VSWR and impedance was OK,
but complete nulls in the pattern off the sides of the aircraft.
Reg,
Fred F.
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