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Though I had never thought much about it, it seems to me there are two views
of MUF:
1) MUF is a prediction of the maximum frequency that can be used at a
given time to communicate between a transmitting site and a desired
receiving site (lots of wrinkles about 50% statistics, using a month's worth
of data, the need to be maybe 20% below the prediction in the real world
etc). This says MUF is a two point number, and at a given transmitting site
at a given time will vary with the azimuth of and the distance to the
desired receiving site. There are many MUF numbers for the transmitting site
because there are many receiving locations on the earth. This is the
ITU/IEEE definition.
2) MUF is a quantity dependent only on the spot on the earth for which
the number is to be computed, i.e. it is similar to a map of critical
frequency. For the case of a critical frequency map, conceptually you pick
a point on the map, put a sounding device at that point, shoot straight up,
look at the data, and determine the critical frequency and mark that number
on the map at that point (in reality you may use models and a small number
of actual measurements). Do the equivalent for F2 layer height. At a given
time there is only one critical frequency contour map for the earth, and
only one f2 layer height map. But as far as I can tell the MUF maps
generated by many of the propagation programs are independent of the site
assumed for the transmitter, just as are (and should be) the layer height
maps.
Can someone clarify this for me, or point me to a source which is clear on
this point?
Bob W2WG
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