On 8/7/20 4:13 PM, Bill Byrom wrote:
See this 1961 IRE paper at the NIST website:
https://tf.nist.gov/general/pdf/2303.pdf
IRE merged with AIEE in 1963 to form IEEE.
Figure 7 shows the calculated amplitude transfer of the ground wave signal vs
frequency and distance. Note that for 100 kHz signals, the ground wave signal
is reasonably strong at 2,000 miles but lousy at 5,000 miles.
As this paper notes, the sky wave reflections are delayed, and this delay
depends on the ionization state of the ionosphere along the propagation path.
This delay is shown in figure 2.
Figure 6 shows differences between daytime and nighttime propagation of pulsed
signals. The received signal is a combination of the ground wave signal and one
or more skywave signals (which are delayed with respect to the ground wave
signal).
--
Bill Byrom N5BB
and such stuff is why Omega worked at VLF frequencies - none of that
pesky skywave - lambda=30km and you're ALWAYS below ionospheric cutoff.
Alas, they made some boneheaded mistakes like making one of the
frequencies an exact multiple of 60Hz.
There is something positively Tesla-ian about Omega with high power low
frequency transmitters into physically enormous antennas - like the one
with the top hat across the fjord. None of this tiny L-band patch
antenna stuff inside a wristwatch.
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