Since I have some experience with 160M short verticals, I will add my
two cents' worth. I operated from Kwajalein, Republic of the Marshall
Islands for 5 and a half years as KX6DS. Four and a half of those years
I was active on 160. I had a very limited space in which to erect an
antenna for Top Band. It was the flat roof of my duplex, which was 33'
x 80'.
Kwajalein is a small(2.5 x .5 miles).flat, coral island. There are no
hills, no obstructions to the radiated signal and it is surrounded by
salt water. I would think that it is nearly ideal for evaluating
antenna performance.
I started operation on Top band with a 26 foot high, inductively loaded
vertical. I laid out 100 radials, ranging in length from 15' to 50',
on the flat roof under the antenna. There was no point in driving
ground rods in the coral. I found the 26 foot antenna to be too
inefficient to be acceptable. I finally ended up with a 62 foot, top
loaded vertical which worked very well. Sixty-two feet is probably
taller than necessary. I would think that 50 feet would work OK. Top
hat loading is the preferred method of resonating a short vertical as it
results in the highest efficiency and widest useable SWR bandwidth of
any load coil arrangement.
I sympathize with those operating from city lots. I did it for years and
know what you are up against. The ground system is by far the most
critical component of the antenna system. Unless you can come up with a
good ground, don't waste your time and money on an antenna.
Of course, almost any sort of matched antenna will allow you to get on
the band and make many enjoyable QSOs. Just don't expect to work DX
under most conditions.
73,
Dave, K4TO
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