Hi Tom,
In your reply to my note, you said:
"Everything I've read indicates signal levels drop as frequency is moved
further below the MUF, and the strongest signals occur just below the MUF.
It is in the Antenna Engineering Handbook section on propagation and also
in other engineering textbooks. They lay the blame to increased absorption
as frequency is decreased below the MUF.
Is that incorrect in some way?"
No, that is NOT incorrect. What you have pointed to is the fact that
ionospheric absorption increases at lower frequencies, roughly as the
inverse-square of the frequency. But that is true no matter what the
MUF might be on a given path. Put another way, you are mixing F-region
and D-region physics. MUFs are F-region matters and at the present time,
no matter what the path, critical frequencies at the peak of the F-region
are so high that 160 meter RF will always be propagated within the lower
ionosphere. So for getting 160 meter RF from A to B, MUFs overhead are
just not important. Signal strength, determined in the D-region, is
another matter.
Next, you said:
"The above two statements seem to support the fact that if MUF is high
from an increased SSN, which also pushes up MUF) on a given circuit, LUF
will also increase. What am I missing?"
It is not what you are MISSING, it is what you ADDED to what I said. I
was speaking only of ionospheric absorption and radiation angles to get
RF past the E-region and into the lower F-region.
By speaking of LUF, you have ADDED noise to the discussion; I did not
do that as it is so highly variable, from QTH to QTH, it is beyond my
ability to discuss in any meaningful way. As I read messages on the
reflector, I think I am doing the right thing as if I try to bring in
man-made or atmospheric noise which, combined with signal absorption,
determine the LUF, I'd be wrong more of the time than right.
Reading your remarks again at this point, they have an more of a HF
slant or flavor to them, the sort of ideas that apply on the upper bands.
160 meters is in the MF range and everything considered, propagation modes
and the like, it is a different ballgame and has to be discussed as such.
Basically, 160 is limited by absorption and noise but there other sorts
of propagation factors that we do not have a handle on. In that regard,
I once told Carl, K9LA, that I thought the word "meteorology" would appear
in the discussion of 160 meter propagation. OK, I now know that the
recovery of the D-region at sunrise is affected by the presence of ozone,
way below the D-region and stirred up by meteorological processes. What
else? You know I have talked about atmospheric gravity waves; that is a
form of high-altitude meteorology. There are probably more; we'll see.
Let me conclude by saying the thing that troubles me is that too much of
the propagation that shows up on the reflector is anecdotal in nature.
Personally, I think of this as a big physics problem and to make any
sense out of it, we have to discuss it in terms of physical variables,
say path geometry, frequency, date and time, SSN, electron density,
gyro-frequency, relevant geomagnetic indices, even the shape of surfaces
of constant electron density. Some of those are readily available, on
the Internet and the like; some are still beyond our reach or reported
on infrequently. But that'll be a path to progress, complete observations
(path, date, time, band) by good operators and, when possible, the
inclusion of physical VARIABLES.
I capitalize that last word as Stratwarm is a "condition" and unless
a report about a radio path is in some way related to just where and
when a Stratwarm occurred (as may be obtained from the meteorological
people in Berlin), that kind of report does not rise to the status of
using a physical variable and contributes very little to further our
understanding. OK?
Have a Happy Holiday Season,
73,
Bob, NM7M
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