Friends in Radio Land
In treating low-band propagation, I am proposing we pay attention to
the state of the neutral atmosphere, in which the ionosphere is
embedded. I suggest we use the control point method, borrowed
with changes from HF propagation programs.
In HF, F-region ionization is the key and its level is determined
by one global, large scale variable, the sunspot number. Thus, a path
fails if ionization (or equivalently the critical frequency) is too low
at one end of the path or the other.
This method assumes ionospheric layers are spherically concentric
and paths are made up of earth-ionosphere hops. But "Super DX"
paths are possible, low-angle chordal hops which are not reflected
by the earth and suffer less ground and D-region losses by absorption.
For MF, I propose the control point method be used but with local,
small-scale variables (atmospheric temperature, presure and
wind speed at the 100 km level. For the moment, data from daily
30 km radiosonde flights would be substituted).
The MF method would use signals from a source transmitter in a stable
atmospheric environment and assumes the path from A to B is always
open, because of sufficient ionization, day or night. Then the
radiosonde data is scanned for days when propagation, A to B, fails.
The T, P or wind speed presumably gave rise to ionospheric tilts
that made the A -> B path fail.
Like HF, "Super DX" paths are possible in MF, now low-angle ducted
paths. Those, also, are beyond the control point method.
The present effort is an attempt to get beyond global and large-scale
magnetic variables on MF and find relevant atmospheric variables that
skew MF paths. It is only the first step.
73,
Bob, NM7M
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