Topband: Top loaded verticals

[Steve Ireland]

Having finally proved my earth system works with an quarter wave inverted-L
antenna (input impedance of around 22 ohms or so), I am looking for
something that puts all its radiation in the vertical plane.  My inverted-L
has got around 60% of the antenna in the horizontal plane, lots of high
angle radiation off the loading wire and consequently often performs rather
like my main inverted vee Tx antenna than a pure vertical.  However, it
certainly does work!

I am interested in finding out what people have found versus using large
top loading coils versus sloping umbrella-type top loading.  Some years ago
I built a VE2CV-type umbrella top loaded wire vertical (Ham Radio magazine,
September 1982) which I still have in the garage, which has a top hat that
hangs down down the 45' or so radiator so that its skirt wire rests at
around 57% of the radiator height (ie around 25').  My concern is that
there is lots of cancellation of radiation with the skirt wire hanging down
so far.

What I am wondering about trying instead is a 50 - 55' top loaded vertical
with a large square section coil wound on a big 3 litre soft drink bottle
or plastic bucket with 3mm or so diameter wire, working against a small top
hat consisting of two wires about 10 - 15' long.  The loading wires and
vertical radiator would be in a tee configuration.

The maximum height I can get the vertical section is around 55' (maybe 60'
if I don't get too much sag in the supporting catenary rope!).

I have also considered trying a simple folded radiator of around 55 - 60'
long and feeding it with an omega (two capacitor match, just a like a shunt
feed tower.  However, I am concerned that with such a short radiator the
efficiency would be very low.

Any experiences with top-loaded verticals of these three types would be
much appreciated, particularly versus each other.  I will summarise the
responses and post to the reflector.

Many thanks.

Vy 73,

Steve, VK6VZ   




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