|[AMRadio] 75 Meters Long Already|
manualman at juno.com
Mon Nov 27 12:37:35 EST 2006
If I remember my propagation stuff, the D layer (lowest layer) is charged
mainly by the sun and hence there is more absorption of lower frequencies
by this layer during the daylight hours. As we get into shorter days, the
D layer has less absorption and during the evening hours, disappears. The
E layer also exhibits some of the same characteristics at lower
frequencies. This disappearance or lack of reflection from these lower
layers and the lack of charged particles being emitted by the sun during
sunspot minimum is another reason why "long skip" is more prevalent at
this time. Your transmitted signal comes off the antenna, travels to a
much higher layer (the lower layers aren't there or almost void of any
charged particles for absorption) where it travels a much greater
distance before being reflected back to earth. At these lower
frequencies, the lower angle of radiation, will cause the wave to travel
farther before it reaches the upper layers to be propagated. So, if you
want to work "short skip" on 75 during the evening hours, it would seem
you need a higher angle of radiation (i.e. lower the antenna; radiate
straight up, etc.).
On Mon, 27 Nov 2006 09:31:17 -0600 "Jim Wilhite" <w5jo at brightok.net>
> I remember (don't all of us old folks) about 20 years ago
> when the skip on 75 was much like the current one. Nothing
> between 100 to 600 miles or very weak and stations out
> beyond that were strong as garlic breath.
> This is really not that uncommon. It follows the 11 year
> cycle and the 22 year cycle as does the upper bands. With
> few sunspots to upset the atmosphere that giant mirror in
> the sky is really working. What puzzles me more than 75 is
> 160. It is not near as good as I expected.
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