Hi Ford,
It seems to me that I've seen some discussion about running
a wire on the ground along the length of a beverage to
connect the grounds between the feedpoint and the
termination. Is this true?>>>
I can't think of a single logical reason in the world to do
that. IMO, it is a very poor suggestion.
First, the resistance of that connection would be very high
because of soil losses.
Second, if it did work to crate a low resistance path the
effect would only be to make the antenna stop working.
Beverages depend on ground losses to function.
This 1 wavelength beverage is 9' off what appears to be very
high conductivity soil. I'm using a transformer instead of
resistors to terminate the end, which means I need a pretty
good ground return to make it work correctly.>>
I know you'll just love to hear this! It isn't that the two
wire revisible system causes a problem, it's that a two wire
Beverage with wide spacing actually adds problems to the
system.
The two wire system with transformers is no more or no less
worse for grounding than a normal Beverage. The problem is
when any beverage has wide-spaced wires in the element, the
reduced surge impedance makes the antenna more dependent on
grounds. There are actually three issues:
First, it makes the antenna feed system more susceptable to
common mode current, so I hope you totally isolated the
feedline from the antenna ground.
Second, it makes any ground problem affect SWR more so you
need better grounds to terminate the antenna correctly.
Third, the wide spacing in a reversable beverage is more
susceptable to unwanted ingress of signals in the
transmission line mode.
For a look at measured ground resistances, check out
http://www.w8ji.com/ground_resistance_measurements.htm
When your antenna surge resistance is 600 ohms, a 50 ohm
ground termination resistance doesn't look so bad.
When the surge impedance is 300 ohms, 50 ohms looks twice as
bad.
The termination becomes less stable because ground
connection loss is a bigger part of termination impedance.
This also aggrivates common mode pickup from the feedline.
The feedline shield is more likely to couple into the
system.
73 Tom
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