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Borrowed from Glenn Hauser's DX LISTENING DIGEST 8-020, February 15, 2008.
PROPAGATION
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160 METER MYTHS
Ed Swynar, VE3CUI, of Newcastle, Ontario, took issue with a statement
in last week's bulletin about the absence of sunspots being great for
160 meters. "Such mythology could not be further from the truth this
year. The band has been most unremarkable this season, to say the
least, and it continues to languish away in the doldrums. I thought
that perhaps it was something at fault at my end: however, many
subscribers to W4ZV's Topband Reflector seem to be of the same
opinion." Readers have sent similar reports about both 160 and 75
meters over the past year. It seems that low geomagnetic and sunspot
activity should be good for the lower frequencies, but perhaps it is
not always the case.
On my website KN4LF 160 Meter Radio Propagation Theory Notes:
http://www.kn4lf.com/kn4lf8.htm under:
5.) Coronal Hole-
.....Coronal Holes occur most often on the downside of a solar cycle and
their absence at the bottom of a solar cycle and at the beginning of the
next, allow for the best medium frequency radio propagation conditions. Many
think it's the lower solar flux values seen at the bottom of a solar cycle
that accounts for improved propagation conditions but it's actually pretty
much a lack of Coronal Holes and geomagnetic storming. (See definition #11.
Geomagnetic/Ionospheric Storm).....
3.) Equatorial Ring Current-
.....A phenomena that acts as a repository for precipitated electrons in the
vicinity of the magnetic equator. The electrons travel by spiraling around
north south magnetic field lines at a frequency called the 'gyro frequency.
The end result is lower latitude propagation path medium frequency
transmitted RF signal blockage and absorption via the D layer. Absorption is
similar to higher latitude Aurora Oval absorption and is inter-related with
same.....
2.) Aurora Oval Blockage, Absorption And Refraction-
.....The aurora ovals "generally" have a negative impact on medium frequency
propagation. If the path over which you are communicating lies along or
inside one of the Aurora Ovals, you will experience degraded propagation in
one of several forms; strong signal absorption, brief periods of strong
signal enhancement, which is mainly caused by tilts in the ionosphere that
allow signals to become focused at your location or very erratic signal
behavior in the form of strong and rapid fading, etc., caused by a variety
of effects such as multi-pathing, anomalous and rapid variations in
absorption, non-great-circle propagation, horizontal or side refraction
and/or scatter (skewing) due to changes in electron density and polarization
changes. (See definition #7. Propagation Path Skewing).....
The bottom line is that propagation conditions will vastly improve on the MF
AM broadcast band, 160 and 120 meters on the upside of solar cycle 24 in
2009 and 2010.
73,
Thomas F. Giella, KN4LF
Lakeland, FL, USA
kn4lf@arrl.net
KN4LF Daily Solar Space Weather & Geomagnetic Data Archive:
http://www.kn4lf.com/kn4lf5.htm
KN4LF Daily LF/MF/HF/6M Frequency Radiowave Propagation Forecast & Archive
Site: http://www.kn4lf.com/kn4lf6.htm
KN4LF 160 Meter Radio Propagation Theory Notes:
http://www.kn4lf.com/kn4lf8.htm
LF/MF/HF/VHF Frequency Radiowave Propagation Email Reflector:
http://montreal.kotalampi.com/mailman/listinfo/kn4lf
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