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Ted Shapas. K9 YOb'
14925 Evers Avenue
Dolton. Illinois 604J 9
o a Better Angle
Observations and Suggestions Involving IIF Radiation
A ngle Manipulation
When HF DX-getting tactics are discussed,
sooner or later the subject will center
around antennas, for the antenna, coupled
with its geographic positioning. will ultimately
make or break a DXer. A status is
eventually achieved, however, when the
serious DXer bas put up the largest and
tallest antenna he cared or dared to, or a
point of "signal strength stagnation" is
reached. For most of us this is a frustrating
level. for it probably still means an S-unit or
three gap between us and the big guns. Even
if you feel you're near the top, however,
there were undoubtedly times when these
extra db would have come in handy. This
article is no magic panacea for combatting a
W3CRA or WSVA in t he pileups, but
knowing a little about radiation angle manipulation
may give you something to think
about along those lines.
Low angle advantages
I think many of us have operated enough
to realize the importance placed upon an
antenna with a very long boom perched
upo n a very high tower. The fellows with the
biggest combinations of these two, possibly
coupled with an elegant location, constitute
the big guns, or the big DXers and contest
Winners.
A maj or reason for their seeming invulnerability
is the very low vertical rad iation
angles associated with such an antenna combination.
For normal F2 propagation paths,
t he best sit uatio n is for your signal to reach
a distant point in the least number of
"hops" o r reflect ions. Up to about 2500
miles or so , o ne hop propagation is po ssible,
but after that, an earth reflection is neces-
78
sary. Now the signal is being decreased by a
number of losses; most pertinent here are
distance losses due to spacial. spreading, and
ground losses at each earthly hop. Distance
loss is of course a function of distance; a
lower reflection angle means less distance
travelled and therefore less loss than a higher
angle, although the difference may only
amount to a db or two. Much more important
are the ground lo sses. While sea reflections
are less critical of incident angle,
ground reflections may result in four or five
db differences per hop between low and high
angles, depending upon frequency (I). Here
is one place where the big guns clean up!
One or two less of these lossy earth hops
experienced by signals approaching from a
high angle and we're ta lking about S-units of
difference. Fortunately, all is not this rosy
for the people with the low take-off angl es,
NBS observations - good news?
The good news is that in most cases. these
things I just talked about occu r only for
"storybook" propagation unde r ideal conditions.
What about the real world? W. F.
Utlaut presented an interesting report along
those lines in our National Bureau of Standards
research journal Radio Propagation
where he made a detailed study o f radiation
angle importance. The results were slightly
astounding (2).
Using a VOA transmitter in Munich,
Germany , and receiving antennas in Boulder,
Colorado (a receiver was also located in
Slough, England , but results were consistent
with those in Boulder), all with carefully
calculated radiation patterns, Utlaut attempter'
to find out if low angles were that
73 MAGA ZINE