An alternative for NVIS might be a tri-folded dipole with a reflector
wire (or wires) on the ground. The spacing between driven element and
ground wire(s) can be adjusted so as to match 50 ohms.
I had good results with this on 40m in Central Africa.
Michael 2E0IHW
On 13/06/2019 23:12, Shirley Dulcey KE1L wrote:
Higher isn't always better. On 40 through 80 meters, relatively low
antennas designed to have a high angle of radiation are useful for
local and regional coverage, using a propagation mode called NVIS
(Near Vertical Incidence Skywave). It's just what you want for
participation in things like traffic nets. An antenna with a low
radiation angle would be far less useful for that type of operation.
But relatively low is not all that low on the lower frequency bands.
The ideal height for an NVIS antenna is in the range of 0.2 to 0.25
wavelengths, and on 80 meters (let alone 160!) that's still pretty
high in the air. An antenna lower than 0.1 wavelengths (which is still
25 feet up on 80 meters) will be much less efficient, though heights
of 0.05 wavelengths are still usable. The heights get less daunting on
40 and 60 meters.
So i guess for most ham purposes, "higher is always better" is pretty
close to the truth. The one exception is 40 meters, where getting an
antenna up well over 0.25 wavelengths isn't that difficult to do for
people with access to trees. That operator might want to have a dipole
up at 0.5 wavelengths to get a lower radiation angle for DX, and a
second lower one for regional operation. On the higher bands it's easy
to get a dipole up higher than the best height for DX, but most people
with the ability to do that will be putting up directional beam
antennas instead.
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