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Re: [TenTec] was OT: Indoor Antenna: re B&W type terminated dipoles

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] was OT: Indoor Antenna: re B&W type terminated dipoles
From: Stuart Rohre <rohre@arlut.utexas.edu>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Fri, 03 Dec 2010 22:10:06 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
Some terminated antennas such as the terminated Beverage are operating 
as a high impedance traveling wave antenna, and thus a resistor to even 
lossy ground would look like a lower RF impedance than the end impedance 
of a long wire.  Thus, you could say the resistor to earth is an "RF 
ground" but as a practical matter, it also serves to dissipate static 
charge build up on the antenna wire.  A DC ground in that case.
Those voltages are so high, even a high value resistor to earth looks 
like an adequate "ground".  On some resistor terminated antennas, you 
have a value of resistance that does not drain much of your RF.

Examples of this are having 100K ohm resistors to static drain both 
sides of a ladder line fed dipole.  The 100k does not pass much current 
if you have an antenna feed impedance of say 1000 ohms.

but the terminations of the Folded dipole, in the center of the unfed 
wire, have been measured to lose one half the power at some bands.  
Naturally the dimensions of the antenna have reaactance terms that can 
in series with the resistor raising the total impedance seen by antenna 
signals.  Thus the statement that ast some bands there is less loss.
-to Rick, I guess the best answer is it depends on the design.


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