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Re: Topband: Broadband Inverted L

To: topband@contesting.com
Subject: Re: Topband: Broadband Inverted L
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Thu, 20 Nov 2014 09:53:34 -0800
List-post: <topband@contesting.com">mailto:topband@contesting.com>
On Thu,11/20/2014 9:25 AM, Gene Smar wrote:
  Don't ask questions and just enjoy the antenna's performance.

A low SWR is NOT an indicator of an antenna's performance. It only indicates a match to the transmission line.

In this case, the low SWR suggests that the antenna is highly resistive. The radiation resistance of an antenna of that height is less than ten Ohms. The rest of the 70 ohms or so of resistance it takes to produce that nice match is LOSS -- a bit in the wire resistance, the rest of it in the radial system.

A connection to earth is NOT an efficient part of an antenna -- the earth is lossy (a big resistor). The only reason for having a driven rod is for lightning protection. It's those radials that are providing a return for antenna current, and 2,000 ft of wire is not a lot on 160M. Over average soil, 2000 ft of wire typically provides a ground loss resistance on the order of 10 ohms; over poor soil, the loss resistance will be higher, over good soil, it will be less.

The high value of loss suggests that perhaps your radials might not be making a good connection to the coax shield, so all the antenna sees is those driven rods.

To understand this, and for some practical ideas for radial systems, study

http://k9yc.com/160MPacificon.pdf

73, Jim K9YC
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