[Lowfer] Guided Waves

[Lyle Koehler]

I agree with Bob that the "Guided Waves" text is more applicable to VLF than
to LowFER frequencies. When you get to frequencies above 100 kHz,
ionospheric absorption can be very high, and very dependent upon time of day
and time of year. Adcock's article on "Propagation of Long Radio Waves" at
http://www.lwca.org/library/lfprop/adcock/lfprop6.htm or
http://www.lwca.org/library/lfprop/adcock/lfprop1.htm (same article;
different resolution on the figures) gives a more complete and quantitative
picture of what can be expected at LowFER frequencies. For those (including
me) who don't want to wade through all the math, Figure 11 tells the whole
story in a nutshell. The curves in Figure 11 show that there is indeed a
"skip distance" for LF skywaves, even at night when the absorption is
lowest. At 200 km, the skywave signal is typically at least 40 dB below the
surface-wave signal. Obviously, very little skywave signal is returned at
high angles of incidence.

Lyle, K0LR