I thought to jump in here with my two cents worth of nonsense, you see I live
in the woods, and don't see to many people these days.....thank God...so here
The single wire Beverage works on the theory of wave front tilt, consulting the
books of 1915 to 1917 by Prof. Zenneck you might of heard of something called
the Zenneck Wave.
On ELF, VLF, and LF, that's all the frequencies or wavelengths below 500 Kcs or
the medium wave broadcast band the wave front travels outward from the antenna
transducer (vertical monopole) along the earth's surface and the bottom side of
the ionosphere. There is no skywave that is received. The earth is a
dissipative medium, which means that its something like a resistance when
compared to the air, therefore the wavefront as it travels forward and outward
starts to tilt forward. Depending on the soil it will tilt forward to
approximately 1 to 10 degrees, over salt water and salt water marsh it remains
perpenicular to the earth's surface. What does this mean? As the wavefront
leans or tilts forward it cuts across the Beverage antenna inducing a voltage
in the wire. This voltage builds in amplitude as it travels to down the wire to
the receiver. Signals coming from the opposite directions do the same, build in
amplitude with one big difference. Upon reaching the terminating resistance the
voltage is dissipated across the resistance. No standing wave reflected back to
the receiver, if the terminating resistance matchs the surge impedance of the
Beverage single wire. Here is where it gets interesting. The resistance is
grounded and the return path goes thru the earth back to the receiver side
ground to complete the path. Therefore, if we treat the Beverage as a single
wire transmission line we find the actual surge impedance impedance of the
antenna as approximately 470 ohms. But we must also include the dissipative
resistance throught the ground. Tom, W8JI, as a pretty good handle on
explaining it to you. Tom is right about the wire under the Beverage is wrong,
not necessary, a no-no, Mr. Misek as it wrong.........
Here's the catch 300 Kcs to 3 Mcs is where transitional propagation takes
place. Waveguide mode theory is no longer valid as we apply in ELF, VLF, and
LF. At 160 meters the ground wave from the transmitter only travels
approximately 100 miles from the monopole, and then vanishes from the surface
of the earth thru absorption. We depend on skywave, chordal ducting, ionosphere
tilting, and ducting South to North. You are receiving the sky wave which is a
tumbling wave front arrivaling at the antenna and traveling the antenna axis.
You are no longer receiving just a ground wave or E Field, but an ellitpical
wavefront. You do not need another wire under a single wire Beverage, it does
absolutely nothing for the antenna system.
There is another way to overcome dissipative ground loss in Beverage antennas,
however, its a little to complicated for me to explain to you presently.
Why multiple wire Beverages antennas, we can add another two wires to a single
wire Beverage, what this does is decrease the velocity of propagation on the
antenna. It also smooths out the impedance bumps in the antenna. Namely it
makes the antenna appear electrically longer than it really is, but at a cost,
the cost is less gain.
Do not confuse the multiple wire Beverage with the 2 wire beverage bi
directional antenna system. It works on a different principle than what I have
described. It is not to well known. You will do fine with a single wire in
multiples of halfwave 3/2 will work just fine. Approximately 800 feet on 160
meters. I would go by W8JI webpage it describes much of the basics and you
won't go wrong.
I use 3 Bi directional Beverages here, NE-SW, SE-NW, N-S, I used RG59 to feed
them. Reflection transformers and on each end 7 ground rods, 8 ft long in HEX
Configuration tied together with no. 8 AWG copper wire.
Master Radio Electronics Officer
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