OK Stuart. I guess what I have gleaned from yours and Jerry's post is, in
the case of a Beverage or similar RX antenna, it is both a DC and RF ground.
I have always been leery of running an antenna which needed a terminating
resistor for transmitting, but I have used Beverages for nearly half my ham
life (almost a quarter century) and I know that they work very well.
The last question that remains to be answered is, when you consider the
merits of a Rhombic antenna, even though it is terminated and you might lose
half your radiated power, the forward gain and low angle of radiation still
make it a very useful antenna.
I don't think I would mind a termination resistor in that case.
Where I have a problem is with antennas like the T2FD antenna.
73
Rick
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Stuart Rohre
Sent: Friday, December 03, 2010 10:10 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] was OT: Indoor Antenna: re B&W type terminated dipoles
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
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
K5KVH
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