Hi Roger,
> I've been contemplating an 80m 4 square for a couple of years. Been
> playing with all the modelling programs. It appears that the high angle
> lobe off the back can be reduced by either changing the driving phase to
> -110, -220 or thereabouts or by increasing the element spacing. Rather
I have no idea why everyone ever settled on 1/4 wl on a side and
90/180 shift. The phase is clearly wrong for the spacing since the
mean element spacing is closer than 1/4 wl when fired across the
corners.
Stretching the array out, assuming you don't run out of feedline, or
more phase delay is better.
I use 120/240 delay or so on mine. It has more gain and a tighter
pattern.
> dual band element. Base loading would be the easiest but least efficient.
> Top loading is better but requires some sort of switch. A trap reduces
> bandwidth too much. I was wondering about a vacuum relay but not sure of
> what voltage to expect. Assuming a 65 ft 3 in dia element with 1kw input
> any educated guesses? Any alternative ideas?
You'd have about 2800 volts RMS at the end with 1500 watts input
with a three inch diameter element in a single vertical. You can
scale it from there to your power.
Element impedances are not all the same in a directional array
with a unidirectional pattern. I'd have to think about how that would
affect end-voltage. My gut reaction is voltage would still be the
same on all elements because the rule of thumb when voltage
feeding elements is they all need the same voltage.
Because of the high voltage, you'd have to be sure you minimized
"leakage capacitance" across the insulator. That would require
some form of compensating inductor.
I'd opt for a decoupling cage around the vertical, or separate
elements and detune or sectionalize the 160 meter elements when
on 80.
73, Tom W8JI
w8ji@contesting.com
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