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.
> Naturally the dimensions of the antenna have reactance 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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