Arthur KB3FJO said: . . . and achieved long-distance propagation by way of a
signal that was reflected or refracted by the bottom of the D layer, and so
didn't suffer the absorption that low-frequency signals usually suffer in that
region.
That's the principle upon which LORAN-C worked (LORAN-C is/was down around 100
KHz). Its long-range capability was due to enough refraction to keep it from
getting too high into the lower ionosphere – where absorption occurs. This also
made is somewhat less susceptible to solar disturbances, as most disturbances
affect the ionosphere above the D region.
But the amount of refraction is inversely proportional to the square of the
frequency. Thus 1.8 MHz RF will necessarily refract (be bent) less for the same
electron density profile, and thus it will get higher into the ionosphere than
lower frequencies like 100 KHz.
Using a readily-available tool (Proplab Pro), we see that 1.8 MHz RF during the
day still goes through the absorbing D region before being bent and returning
to Earth. Thus "normal" absorption combined with transmit power, antennas, and
noise environment determines how far 1.8 MHz will go during the day. This
exercise goes a long way in debunking the myth that 160m is only good for short
local contacts during the day – but it depends on your station capability.
As a side note, if one plays with PropLab Pro enough one will recognize from
the ray traces that the extremely low elevation angles on 1.8 MHz at night
appear to offer an advantage over the "normal" higher elevation angles. I
believe this is why VE1ZZ does so well – his location allows a good amount of
energy at the extremely low angles. Whether land-locked guys can take advantage
of this is what's being discussed right now on this reflector.
Carl K9LA
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Remember the PreStew coming on October 20th. http://www.kkn.net/stew for more
info.
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