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From: "james moritz" <j.r.moritz@herts.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
Date: Thu, 27 Jul 2006 15:19:49 +0100
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Subject: RE: LF: Tapped loading coil design spreadsheet
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Dear John, LF Group,

This design approach would work fine if there was no or negligible =
coupling
between the portion of the coil "below" the tap, and the portion =
"above",
i.e. if the loading coil was divided into two separate coils at the tap
point. Then you would indeed have an L network as you describe. This =
would
be approximately true with a "long, thin" coil, with large =
length/diameter
ratio and well-spaced turns. The limitation is that it can only match to
antenna resistances less than the TX output resistance. But the =
important
difference in the amateur type of tapped loading coil is that it has
substantial coupling between the two sections of the coil, and the =
resulting
mutual inductance allows an antenna resistance substantially higher than =
the
TX output resistance to be matched.

Cheers, Jim Moritz
73 de M0BMU

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of John Andrews
Sent: 27 July 2006 14:58
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Tapped loading coil design spreadsheet

Jim,

I have always viewed tapped loading coils as a high-pass "L" network,=20
where the upper part of the coil leaves a small amount of capacitive=20
reactance, representing the "C" in the network. The shunt inductor is=20
the part of the coil below the tap. The issue is then to design the coil =

for the inductances above and below the tap. In the couple of these=20
calcs I have done, I had accurate R+jX readings of the antenna in=20
advance. That may be more difficult for amateur work.

John Andrews, W1TAG