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Re: [TenTec] Amplifiers or system efficiency.

To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: Re: [TenTec] Amplifiers or system efficiency.
From: "Stuart Rohre" <rohre@arlut.utexas.edu>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Mon, 6 Aug 2007 16:16:24 -0500
List-post: <mailto:tentec@contesting.com>
Alan, absolutely a great post, and well said.  You are right on the money! 
Effective power is the key.  An improved or efficient antenna is the lowest 
cost route to effective radiated power.

A point was made in the QRP forum at the local ham convention Sat.   Even if 
you are using one of the shortened antennas, you still have to keep the high 
voltage ends well away from conductors and screening foliage, or other 
detriments to the high near field levels.

And the high current magnetic field concentration near the feed point should 
also be protected from coupling to conductors.

A dipole can be shortened to 60 per cent of full length and maintain 
efficiency in the greater than 90 per cent
value.  You just have to have it in the clear of detractors from its field. 
Low profile antennas like the Moxon rectangles can provide beam performance 
in less than traditional Yagi dimensions.  Use of low loss insulators, 
conductors,  and fasteners is key to small antenna use.

An easily elevated small beam may be the answer for aging hams.  The masts 
from Force 12 that were marketed for portable use come to mind.  Motorizing 
such an elevating cable for that mast might be fairly simple.


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