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Re: LF: LF-antenna with top load

To: [email protected]
Subject: Re: LF: LF-antenna with top load
From: "Dick Rollema" <[email protected]>
Date: Thu, 16 Sep 1999 14:01:58 +0200
Reply-to: [email protected]
Sender: <[email protected]>

Mike, G3XDV wrote:


1. No top load
Efficiency: 10.8%
2. One horizontal top load wire of 5 m
 Efficiency: 12.5%
4. One horizontal top loading wire of 10 m
Efficiency: 11.9%

6. One horizontal top loading wire of 20 m
Efficiency: 10.0%

Dick,

There's something wrong here isn't there?. You have a reducing
efficiency for increasing top load length. Surely that can't be right.

Yes, I agree it looks strange. But it results from the way  efficiency is
calculated: radiation resistance divided by the sum of radiation and loss
resistance. When the loss resistance increases more than the radiation
resistance efficiency goes down.  In the real world the actual efficiency
will certaily get better as the small increase of wire loss is almost
swamped  by the total resistance of the system: earth loss + coil loss +
wire loss.
What really matters is the increase of Rs.

It is better to ignore the efficiency figures; I used them only to calculate
Rs from the real part in
Z = R + jX


73, Dick, PA0SE



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