Signals and mountains
radiation angles give us short hops and low radiation angles give
us long hops. High radiation angle energy can make it to the DX,
but because many more hops are required to get there, the signal
will be weak or non-existent.
-- Rick Hiller, W5RH, in Low Band DX Antennas
virtually nothing about radio waves and antennas, but this page
outlines how I think about signals arriving at my antennas. It explains
why my contest scores were so bad from my first forays in 2002 till
is a "good" radiation or take off angle for DX contesting?
The general feeling is: the lower the better. If you can hear them,
concensus is you can probably work them.
strongest long-distance DX signals arrive at an angle of incidence
of 5 to 15 degrees (that's the
Geometry dictates that the same station's signals arriving
at 25 degrees (green line)
have to hop more times to get to you. Yes,
you might still hear them, but they will be a lot weaker.
Let's say my yagi antenna hears best when signals come in at 25
degrees. If the station is a long way off, there isn't much energy
in those 25-degree signals because they have to hop many times,
each hop taking away more energy. Still, my yagi scoops up enough
of the 25-degree energy (gain) so I can hear and work those stations
-- although often only marginally.
5-degree signals are a lot stronger, having taken only a couple
of energy-sapping hops. The yagi does hear these low-angle signals,
but it has very little gain (not collecting much energy) at low
angles. Bottom line: every bit of those low-angle signals you can
get into the antenna helps you hear better.
and Blocked Signals
with a mountain blocking European and North American
signals below 13 degrees (as my mountain was -- see
map), I had no low angle signals to work with. I was only hearing
signals arriving at angles above 13 degrees -- meaning anything
I heard was getting to me at high angles, which for DX takes lots
of hops (blue
line). On-air experience bears
this out very well.
an improved visual horizon toward Europe now allowing signals down
to 0 degrees, and North American signals down to 5 or 6 degrees,
my antennas at least have a chance to hear those stronger (fewer
hops) signals from a long way off, and the strong high-angle stuff
from closer in, too.
I'm no expert source -- real ionosphere jockeys won't think much
of my halting analysis but this isn't intended to be a scientific
treatise; it's just a study of my situation and on-air experiences.
It quite nicely explains the on-air performance of my station pre-April
2004 and what I hope to hear after April 2004.
For good reading about how signal angles affect
your ability to hear and work DX, check these Web pages:
of Radiation: What Is It?
eHam article by K2WH
Mildly technical, a good primer
Great tutorial and very complete glossary of terms