Summer 2009 Issue
Six-Meter Paths of Glory
As did the summer of 2008, the summer of 2009 represents a unique opportunity for 6-meter operators to take advantage of the quiet geomagnetic conditions associated with the long solar minimum in the area of long-range multiple-hop sporadic-E contacts. Geomagnetic activity generally has been observed by 6-meter operators to be an impediment to sporadic-E conditions, particularly when geomagnetic storms occur such that these storms create aurora activity, as was experienced in the June 2004 VHF contest, with little sporadic-E.
Last year, CQ VHF presented a series of articles on the U.S. to Japan contacts that were made on 6 meters during June 2008. As suggested in the articles, the quiet solar activity allowed for multiple-hop sporadic-E activity to occur, particularly in the links over the aurora zone, which have been suggested to be a PMSE (Polar Mesophere Summer Echo) related phenomenon.
At the time of this writing, with the current
solar activity there is reasonable expectation that similar events may
occur this summer as well between the US and Japan. There also may be some
new discoveries that could result in “first” contacts between different
countries on 6 meters. The key is that some hams in different areas of the
world, particularly in the equator and Northern Hemisphere regions, listen
consistently on 6 meters. Hams in new locations on 6 meters are going to
be at the forefront of some of the new multiple-hop paths that are going
to be discovered.
In 1957 a graduate student by the name of Dr. Ernest K. Smith wrote a thesis for his doctorate degree that would later become a scientific book, Worldwide Occurrence of Sporadic-E, published by the National Bureau of Standards, then a part of the US Department of Commerce. It is probably the first book that was dedicated to the phenomenon of sporadic-E. The book made extensive use of worldwide ionosonde station data that was collected from 1948 through 1952.
The majority of ionosondes were set up shortly after World War II, and they consisted of a transmitter that put out a sweep spectrum of frequencies from 1 to 20 MHz in a straight-up or vertical path. Any return signal that reflected off a formation in the ionosphere could be measured and recorded as the critical frequency (fo).
The hourly data collected by the different
ionosondes was used to generate the worldwide maps that were used in
Smith’s thesis to tabulate the percent of sporadic-E occurrences where fo
is greater than 5 MHz. An fo value of 5 MHz represents an MUF (maximum
usable frequency) almost 28 MHz, as shown in figure 1. One of the maps
that Smith created is presented in figure 2. Note that there are no
ionosonde stations located in the equatorial zone to collect sporadic-E
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