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ARRL Propagation Bulletin ARLP031 (2006)

ARLP031 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 31  ARLP031
From Tad Cook, K7RA
Seattle, WA  August 4, 2006
To all radio amateurs 

ARLP031 Propagation de K7RA

Last Friday, July 28, a high speed solar wind stream hit earth, and
created a geomagnetic disturbance that drove the planetary and
mid-latitude A index up to 29 and 26, respectively.  This actually
began in the early hours of Friday UTC, which was Thursday afternoon
and early evening in North America.  Both mid-latitude and planetary
K index rose to six.  If you noticed some periods of high
absorption, or when the only propagation seemed to occur north to
south, that would be why.

Now we are moving slowly toward the fall equinox, and HF radio
conditions tend to get better when the hours of light and darkness
are equal between the northern and southern hemispheres.

This week we saw the average daily sunspot number rise over five
points to 20.  We will see little variations like this as the solar
cycle declines toward its minimum next year.  Solar activity still
seems too high to be at the bottom though.  A glance at graphs of
smoothed sunspot numbers shows we are still experiencing more
sunspots than the minimum back in 1996.  Check the graph at on the very bottom
of the page, and on
page 9.  Further down on page 9, you can see that the prediction for
the smoothed sunspot number for August 2006 is the same as for
August of next year, and the minimum is somewhere in between.  That
means according to this graph, a year from now the new solar cycle
will be bouncing back from the minimum, and rising past the point
where we are now.  The smoothed numbers are averaged over many
months (I think this graph uses a moving six-month average) to help
us see past the ''noise'' of daily variations.  This graph shows a
minimum in January 2007, only five months from now, with a smoothed
sunspot number of five.

July is over, so we can look at some monthly averages of sunspot
numbers and solar flux.

The average daily sunspot numbers for the months July 2005 through
July 2006 were 68.7, 65.6, 39.2, 13, 32.2, 62.6, 26.7, 5.3, 21.3,
55.2, 39.6, 24.4 and 22.6.  Average daily solar flux for the same
months was 96.5, 92.4 , 91.9, 76.6, 86.3, 90.8, 83.4, 76.5, 75.5,
88.9, 80.9, 76.5 and 75.8.

Over the past week I've been playing with the excellent HF radio
propagation software, ACE-HF Pro, written by Richard Buckner.  ACE
is an acronym: Animated Communications Effectiveness, and it was
originally written for VLF communication with submarines.

This program is really a treat.  ACE-HF Pro is based on software
that Buckner wrote for military and commercial clients while at
Collins Radio, and it uses the VOACAP engine.  He has a new version
2.05 out, which is much more Windows-friendly than earlier versions.
With it, you can produce colorful graphs that make it easy to
visualize propagation over time and space, and users can even
animate the results to produce a movie of signal coverage over time.
Unlike other propagation programs I've used, it also makes 160-meter
predictions, and attempts to predict sporadic-E skip.

Tomas Hood, NW7US, who writes the monthly Propagation column for CQ
Magazine, did some detailed reviews of ACE-HF in the May and July
issues.  He also has reviews online at .
Among the interesting and unusual features is the ability to factor
antenna radiation patterns into the calculations of propagation

David Mays, W8UI of St. Marys, West Virginia sent some big beacon
lists for HF and six meters, put together by G3USF.  See them at and  Also, Bruce Brackin, N5SIX
of Brandon, Mississippi commented on Larry Godek, W0OGH and his wish
for a database of 10-meter repeaters searchable by frequency, all
across North America, rather than lists sorted by state.  This would
help him identify the location of 10 meter repeaters when they
appear.  David recommends getting the ARRL TravelPlus CD, then
exporting the data to a CVS file and sorting it in a spreadsheet

If you would like to make a comment or have a tip for our readers,
email the author at,

For more information concerning radio propagation, see the ARRL
Technical Information Service at For a detailed
explanation of the numbers used in this bulletin, see An archive of past
propagation bulletins is at .

Sunspot numbers for July 27 through August 2 were 23, 17, 19, 23,
25, 11 and 22 with a mean of 20. 10.7 cm flux was 74.4, 72.6, 73,
73.9, 72.4, 72.8, and 72.1, with a mean of 73. Estimated planetary A
indices were 9, 29, 5, 5, 12, 12 and 10 with a mean of 11.7.
Estimated mid-latitude A indices were 5, 26, 3, 3, 11, 9 and 7, with
a mean of 9.1.


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