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ARRL Propagation Bulletin ARLP028 (2010)

ARLP028 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 28  ARLP028
From Tad Cook, K7RA
Seattle, WA  July 16, 2010
To all radio amateurs 

ARLP028 Propagation de K7RA

Two new sunspot groups appeared in the last week, groups 1087 and
1088.  1088 lasted just one day, on July 13, 2010 with a relative
area of 10 (millionths of a solar hemisphere).  Sunspot group 1087
had a relative area from July 9-15 of 30, 100, 120, 130, 70, 100 and

Average daily sunspot numbers this reporting week (July 8-14) rose
2.9 points to 18.9, and average daily solar flux was up 6.4 points
to 79.2.  Predicted solar flux for July 16-23 is 76 on each day,
then 74 on July 24-27.  This is lower than recent forecasts

Predicted planetary A index for July 16 is 10, followed by 5 for
each day through July 22.  The next rise in planetary A index is
July 23-28, when it is predicted to be 18, 12, 10, 8, 15 and 10.

Geophysical Institute Prague predicts quiet geomagnetic conditions
July 16-21 and quiet to unsettled on July 22.

On Wednesday, July 14 there was an interruption at in the portion of the STEREO image that
faces earth, but by early Thursday morning it was restored.  On July
18 around 1000z the STEREO mission coverage will reach 91 percent of
the sun's surface.  In February 2011 the Solar Dynamics Observatory
( will provide the data to the STEREO
online display that appears around the zero degree meridian, and
solar coverage should be at 100 percent.

Due to movement of the STEREO craft, as the gap closes on the far
side, a new one facing earth will begin in January 2011.  Eventually
the two spacecraft will work their way around the sun and return to
their original position by 2024.

In another example of sporadic-e propagation, Erik Beck, who I think
might be N7FYO, reports "As I was driving outside Providence Rhode
Island, at about 9:00 AM I was able to pull in loud and clear on
90.1 MHz, WXVS, Waycross, GA.  By far the longest DX FM station I
have encountered!  This with a car radio and an in-window antenna!"

WXVS runs 79KW with a tower just north of the Okefenokee Swamp,
around 1,000 miles from where Erik was driving.

Vince Varnas, W7FA of Aloha, Oregon wrote to say this about E-skip:
"As the Sporadic E skip distance on the lower frequencies shortens,
the E skip on higher (VHF) frequencies appears and is longer in
distance (single hop).  Thus, VERY short skip on 10 meters means
longer skip on 6 meters and probably E skip on 2 meters at a still
longer distance".  He says that one way to spot 6 meter openings is
to watch ten meters.

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 an explanation of the
numbers used in this bulletin, see An archive of past
propagation bulletins is at  Find more good
information and tutorials on propagation at

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

Instructions for starting or ending email distribution of ARRL
bulletins are at

Sunspot numbers for July 8 through 14 were 11, 12, 18, 25, 22, 28,
and 16 with a mean of 18.9.  10.7 cm flux was 75.6, 80, 79.9, 82.6,
80, 78.5 and 77.7 with a mean of 79.2.  Estimated planetary A indices
were 3, 5, 2, 5, 5, 3 and 11 with a mean of 4.9.  Estimated
mid-latitude A indices were 2, 4, 0, 2, 2, 1 and 7 with a mean of


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