Peter, you might want to look at the pdf copy of the original article.
There is no "trap" per se in the design.
Instead, there is a clever arrangement using a parallel LC circuit that
provides inductive loading on the lower frequency and capacitive loading on
the higher frequency. It just so happens that this LC circuit does resonate
at a frequency that is about halfway between the low and high bands of the
antenna.
The cool thing about this design is that the entire length of the antenna
is used on both bands; providing a bit of gain on the higher band in a
manner similar to a collinear dipole or distributed C design.
73,
Gerald K5GW
In a message dated 12/16/2010 8:08:25 A.M. Central Standard Time,
dj7ww@t-online.de writes:
It will not work on two bands without a trap
73
Peter
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Jim Thomson
Barry's designs use a loading coil in each leg rather than a trap, and
the coils are roughly at the point where the insulator would be for a
half wave on the higher band. Then the coils, and a bit more wire. The
160/80 version is roughly 160 ft long, the 80/40 version is a bit under
100 ft.
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