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

To: tentec@contesting.com
Subject: Re: [TenTec] was OT: Indoor Antenna: re B&W type terminated dipoles
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Reply-to: geraldj@weather.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 05 Dec 2010 12:54:17 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>

On 12/3/2010 10:10 PM, Stuart Rohre wrote:
> 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.

Typical terminating resistors for Beverage run 600 to 1000 ohms, a lot 
higher than a ground rod resistance.
> 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.

That efficient?

> Naturally the dimensions of the antenna have reactance terms that can
> appear
> 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.
> -Stuart
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