> How important/valid is statement:
> "Both verticals has to be the same" for 1/4 wave
> verticals/space to be fed in phase?
> Can one be shunt tower and other inverted-L ?
George,
Here is what happens....
When we series feed and antenna at a current point, the
phase and level of current is right what it is at the
feedpoint. Phasing two same design elements for a perfect
null requires equal current, and it is easy to do.
When you feed at a voltage maximum, two identical elements
require equal voltages instead of equal currents.
When you have one element shunt fed and one series fed, the
shut feed arm causes an additional phase shift. It also
causes the element to NOT need equal current at the
feedpoint compared to any other element because you are not
applying power at the current maximum! You also are not
applying power at a voltage maximum, so it needs something
other than equal voltage and equal currents.
I fed a G5RV at 100 feet (as a T antenna) and phased it
against a 120 ft shunt fed tower, and had an east, west, and
broadside pattern with very deep nulls. I set it up with a
test oscillator placed in the areas where I expected nulls,
and built an adjustable phasing network for each pattern
(east, west, broadside).
You can certainly make something like that work, especially
broadside where a few dozen degrees of phase error and the
amplitude errors won't change gain much. You'll probably
have difficulty getting a clean pattern without compensation
for the phase and level errors between the two elements.
73 Tom
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