[Elecraft] What Vertical Antenna Do I Need?

[Ron D'Eau Claire]

Fred N3CSY asked:

I'm another limited space, restricted community
ham (for now).  I've been considering different
types of verticals which might be best.  I THINK,
I'm looking for an antenna which:

  - vertical ?
  - no radials
  - no counterpoises
  - no guy-wires
  - 40 thru 10
  - maybe 4 shorter buried radials (if I must)
  - not a lot of "visual" space, for neighbors

We have a MOBILE Home (mostly plastic, and
wood) - which sits on a slab of concrete,
surrounded by 8x8 wood timers, 2 feet high on
front side of mobile.  Can easily get UNDER
mobile, thru removable siding.

Park owner, OK'd a "marine antenna" - whatever that
means to him.  We live on shore of St. Lawrence
River - Canada in the distance.

What commercial or home-made antenna could suit
my bill?

------------------------------------

To most people familiar with ships a "marine" antenna is a 20 foot whip,
usually a robust self-supporting fiberglass pole that is mounted with side
brackets on the side of the house on smaller boats or on the side of one of
the stack on large ships or, on large ships, is mounted at the base with a
ring about 1-foot in diameter that is bolted to the steel deck. They work FB
as Marconi antennas (1/4 wave or shorter worked against ground) because the
"ground" on a ship is the best you'll find on the earth: miles and miles of
salt water. 

With such a ground those antennas are astonishingly effective. A big part of
the efficiency comes not from the immediate ground connection, but from the
fact that out in the Fresnel zone some wavelengths from the antenna where
the electromagnetic waves interact with the earth, the "earth" there is very
good conducting salt water. 

Your requirements include "no radials". In that case you might go with one
of the so-called "ground independent" verticals such as the Cushcraft R6000.
They are electrically 1/2 wavelength long, so they don't require radials but
they are *not* as efficient as a true half-wave antenna. Still, a 40-10 or
40-6 meter antenna like the Cushcraft is only a bit over 20 feet tall, which
should meet the demands of the park owner, and will deliver good performance
in the smallest space. The only issue will be that instead of the clean,
simple fiberglass pole that one usually sees on boats, these antennas have
several vertical sections all interconnected. 

On land you'll need radials with a typical marine whip. The closer to the
ground, the more radials you'll need for a given efficiency. The idea of the
radials is to intercept the RF currents and have them flow in good
conducting copper instead of through the lossy earth. If they have to be on
the ground, the "rule of thumb" the FCC and broadcast engineers have used
for over half a century is to have 120 radials 0.2 wavelengths long
radiating from the base of the antenna. If you can raise the radials even
only five or six feed above the earth, half a dozen are just as effective as
the 120 on (or in) the ground. Fewer will work, but not work as well. 

Such an antenna with, say, four elevated 1/4 wave radials, will work quite
well on 15 and 20 meters, work fair on 40 meters and even provide some
contacts on 80, although there it'll be a very inefficient antenna. 

Ron AC7AC