Rick:
Don't think of it as a parallel-tuned circuit; think of it as an
impedance-matching transformer with the capacitor cancelling the inductive
reactance component introduced by the transforemer and presented at the
low-impedance side.
As a transformer, it can have either two separate windings or be an
autotransformer (tapped coil). It's usually simpler to use the latter.
An alternative is to tap down on the capacitance and tune out the capacitive
reactance with a coil, but that seems much more difficult.
I have attached an Excel spreadsheet that I created to end-match an 80m
Inverted Vee dipole. The calculations are for three values of impedance at
the end feedpoint, 1000, 1500 and 2000 ohms--the antenna is presumed
resonant so these impedances are real. The analysis models the
autotransformer as two tightly coupled windings; X1 is the self-reactance of
the input winding (tap to ground)and X2 is the reactance of the output
widning (feedpoint to ground). You can scale the L and C values for 160m
(double L, half C). The voltage and current listings are for 1500 watts; for
100W, reduce them by a factor of almost 4.
Garry, NI6T
-----Original Message-----
From: topband-bounces@contesting.com
[mailto:topband-bounces@contesting.com]On Behalf Of Rick N6PE
Sent: Monday, May 30, 2005 10:33 AM
To: Topband 160
Subject: Topband: 1/2 wave vertical
Hello all,
When matching a 1/2 wave vertical running 100 watts if I use a parallel
tuned circuit is it recommended to tap the coax down the coil or link couple
it with another winding?
Is there a better way to match it, say with just capacitors?
We are thinking balloon vertical for FD.
Thanks,
Rick Darwicki -= N6PE =-
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