The lower that losses can be made within the antenna, the higher the
current
for a given applied power, so the better the DX result by sky wave mode.
Carrying out field strength readings a few km away would be more of an
investigation of the ground wave mode rather than the manner in which the
antenna actually launches "rays" that can then reflect off the ionosphere.
So it is not easy to investigate the impact of elevated radials with
respect
to radiating energy that goes into sky wave mode.
Most text books are concerned with efficiently launching ground waves and
having reliable coverage. The matter of how the antenna launches energy
that supports sky wave mode of communication is not so easy to find. Any
comments on that?
73, Bob ZL2CA
Traditional thinking is that maximum =low angle= sky wave occurs in a
Marconi antenna at the same time as maximum ground wave. This assumes that
low angle sky wave is always optimum. This is plainly the case using simple
theory, but there must be occasions when a higher angle will 'match' the
ionospheric conditions at the time. Amateur radio differs fundamentally from
commercial radio in that we can make use of unreliable anomalies that
produce much better propagation than the average. It may be that such
anomalies exist at higher angles of radiation.
The subject of designing for a vertical angle of radiation appears to be
largely unexplored, except to get this 'lowest possible' angle.
When several UK stations used loop antennas, I noticed that they had fading
at much shorter distances than those using Marconis. This was at about
300km, whereas Marconi users experience fading at about 500km. Since this
type of fading is caused by interference between the sky wave and ground
wave, it suggests that the loops had a higher angle of radiation. Is this a
function of loops, or is it possible to steer the vertical angle by altering
the feedpoint?
I have been using a 3m loop for receive recently with interesting results. I
can receive CFH during the daytime much stronger and much more often than
with my Marconi. At night, these differences are less. Alan, G3NYK, has said
that daytime transatlantic propagation is by a different mechanism than
night-time. Is my reception difference perhaps a function of angle of
radiation?
Mike, G3XDV
http://www.lf.thersgb.net
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