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ARRL Propagation Bulletin ARLP002 (2010)

ARLP002 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 2  ARLP002
From Tad Cook, K7RA
Seattle, WA  January 15, 2010
To all radio amateurs 

ARLP002 Propagation de K7RA

Recent sunspot activity remains strong.  Weekly averages of daily
sunspot numbers over the past six weeks as reported by this bulletin
were 1.9, 21.1, 31.4, 21.9, 14.6 and now 26.4.

Sunspot region 1035 re-emerged as region 1040 on January 7, and his
been growing steadily.  For January 7-14, the total area of region
1040, as expressed in millionths of a solar hemisphere was 80, 40,
70, 130, 300, 300, 380 and 290.  It has passed the zero-degree
meridian (the imaginary vertical line on the visible Sun that faces
straight toward earth) and now looks like it has another four days
before it crosses the Sun's western horizon.  This is seen on the
STEREO web site at,

A bright area that may be a sunspot is slipping out of the dark
area, the approximately 12.8% of the Sun unseen by the STEREO craft.
This may reach our Sun's eastern horizon just after region 1040
passes over the western horizon.

Ed McKie, KB5GT of Yazoo City, Mississippi wrote to ask how high the
solar flux has to go before he starts noticing a big difference in
HF propagation.  He wondered if we could use 20 meters as an

I told Ed I've heard that flux is a good relative indicator related
to sunspot activity, but I've also been told that the popular
prediction software is best used with sunspot numbers.  The
algorithms are based on the predicted smoothed sunspot number, which
of course is an average going six months back and six months into
the future, so half of it is a guess.

The programs are a statistical guess based on the conditions being
at least as good as predicted half the time and less than that the
other half, based on that smoothed number.

The latest predicted smoothed sunspot numbers are here:

Although the word "weekly" appears in the URL, I believe this is
updated monthly, early in the month.  The current prediction was
created on January 5.

Another source is the Preliminary Report and Forecast of Solar
Geophysical Data from the NOAA Space Weather Prediction Center.
Usually in the first issue of any new month they will give a new
table of predictions, along with a graph.  You can find it at  The recent issue 1792
has the information on page 9.

One approach would be to make a rough estimate, month by month as
the smoothed sunspot number increases, to specific locations from
your QTH, using W6ELprop.  There is a good introduction to using
W6ELprop on Carl Luetzelschwab's, K9LA, site at,  Click on "Tutorials," then
"Downloading and Using W6ELprop."

KB5GT is located at 32.867 degrees north latitude, 90.367 degrees
west longitude.  Let's try a prediction from his location to Spain,
for mid-February, with the predicted smoothed sunspot number of
17.4, and look at 20 meters.

Using 14.1 MHz, on February 15 we see the A and B rated (meaning
good probability of a path) period runs from 1630-2000z, with
relative signals at 25-28 dB above a half microvolt.

On March 15 and a smoothed sunspot level of 20.2, the A-rated
opening starts an hour earlier at 1530z, but 4 dB lower than the
previous month, then from 1800-1830z it drops about 8 dB.  The
B-rated period ends at 2200z.  So the opening should last longer,
but with lower signal levels than February.

The following month using 23 for the smoothed sunspot number, the
opening starts slowly, with signal levels gradually improving until

You can see how this exercise gives one an appreciation for seasonal
variations more than anything.

Skipping ahead to September with a sunspot number of 37.1, we see
another slowly improving opening, ending around 2330z.  Note also
that the 17 meter conditions are quite good.  In February any 17
meter opening was predicted as very brief.

Looking at November 15, 2010 using a sunspot number of 42.5, in the
dark Northern Hemisphere the openings are short.

Go to September 2011, and using a sunspot number of 67.9, 20 meters
is open longer.  Note also the odd improvement in the odds at 0430z.

So when has it improved?  The improvement is gradual, and there
aren't any rules for what is "good enough."  As you learn about your
station's capabilities you will form your own opinion.  But don't
let the perfect be the enemy of the good.  By all means, get on the

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 web page at, For a detailed
explanation of the numbers used in this bulletin, see An archive of past
propagation bulletins is at

Monthly propagation charts between four USA regions and twelve
overseas locations are at

Instructions for starting or ending email distribution of this
bulletin are at

Sunspot numbers for January 7 through 13 were 15, 14, 20, 25, 35,
35, and 41 with a mean of 26.4. 10.7 cm flux was 78.1, 77.4, 81.7,
84.4, 89.2, 93.3, and 90.5 with a mean of 84.9. Estimated planetary
A indices were 1, 2, 1, 2, 6, 3 and 6 with a mean of 3. Estimated
mid-latitude A indices were 0, 0, 1, 2, 4, 2 and 4 with a mean of


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