ARRL Propagation Bulletin ARLP035 (2010)

ARLP035 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 35  ARLP035
From Tad Cook, K7RA
Seattle, WA  September 3, 2010
To all radio amateurs 

ARLP035 Propagation de K7RA

Over this past week four new sunspot groups appeared.  Group 1101
was already in place since August 24, and 1102 emerged on August 29.
On September 1 both new sunspot groups 1103 and 1104 appeared, and
on September 2 sunspot group 1105 arrived.  Over August 26 to
September 2 the daily sunspot numbers were 23, 11, 11, 25, 28, 27,
51, and 52 and over those same eight days the relative total size of
all the spots (in millionths of a solar hemisphere) was 100, 100,
130, 170, 180, 220, 270 and 180.

Average daily sunspot numbers for August 26 to September 1 rose over
17 points to 25.4, when compared to the previous 7-day period.
Geomagnetic indicators began the week showing unsettled conditions,
but they calmed down to quiet levels again.

Now that August is over, we can look at average sunspot numbers for
the previous few months.  The 3-month trailing average of daily
sunspot numbers ending in August was 23.2.  That is up from the
previous two periods ending in June and July, but lower than earlier
this year.  The 3-month trailing averages of daily sunspot numbers
ending in March through August was 25.7, 22.3, 18.9, 16.4, 20.4, and

U.S. Navy and NOAA predict solar flux values of 78 for September
3-4, 76 on September 5-10, 78 on September 11, and 80 on September
12-14.  Predicted planetary A index for the same period is 5 on
September 3-4, 8 on September 5-7, and 5 on September 8-14.
Geophysical Institute Prague predicts quiet conditions on September
3-4, unsettled September 5, quiet September 6, quiet to unsettled
September 7, and quiet September 8-9.

Robert Wood, W5AJ of Midland, Texas wrote: "Are we now two Sun
rotations from the famed WW SSB contest weekend? And is that any
indication of conditions for that weekend?"

Two solar rotations is about 55 days, which would be Thursday,
October 28, just before the CQ World Wide SSB weekend.

I don't think we can project ahead based on current conditions
because we're not seeing any pronounced recurring activity.  Solar
activity is still very low.  Two rotations back is Saturday, July
10.  Looking back since July 1, we saw sunspot numbers above 40 on
July 23-24, August 5-13 and September 1-2.  The number 40 is purely
arbitrary, of course, but there is no pattern there based on period
of solar rotation.

For geomagnetic activity, since July 1 we had planetary A index over
15 on July 27, August 3-4 and August 24-25.  The last period is
about one solar rotation after July 27, but there wasn't a period of
geomagnetic activity corresponding to early August in early July.

In decades past we've seen periods of intense activity that would
come around for several solar rotations, but we aren't currently
witnessing any pronounced solar activity.

W5AJ is a very active DXer and contester, and has a web page
detailing some of his activities at  Many of
the pages have audio snippets from various contests.

In an email, Ron Alexander, KD8ID of Lansing, Michigan wrote, "One
of the complaints that fascinates me is 'the higher bands are not
open or the bands are very poor.' I have not found this so; there is
always a contact to be made during the early morning, day (weekends)
or evening on 40 through 10.

"The key to good propagation, as you know, is the antenna.  Amateurs
buy top of the line transceivers and don't put any money into the
antenna.  You know, an FT-9000 with a shortened dipole.  Sunspots
help a lot, but antenna selection has a lot to do with making
contact.  Also, power helps, but it does not help you hear someone
better.  The antenna does and always will.

"I consistently work VKs and ZLs in the early morning with 200 to
300 watts on 40 phone. I use a Mosley Pro-96 at 72 feet which has a
36 foot boom, nine elements, 3 active on 40, 4 active on 20, 17, 15
and 12, and 6 active on 10.  They come in loud and strong unless we
are having a K index in excess of 4.

"Of course, not everyone has the luxury of a large beam based on the
area they live.  The point I am making is, the bands ARE open, it's
just a matter of having the right thing up in the air to make a go
of it.  Additionally, one must understand the practice of
propagation to know where to go to find contacts.  There is a wealth
of information out there including SEC/NOAA education on
understanding solar cycles, sunspots, solar flux, along with A and K

Ah, to have such a nice antenna high in the air!  As Ron says, not
everyone has the advantage of a large beam, but he is correct that
the antenna is all important.  You can get a nice look at Ron's
antenna at, and be sure to click on the
photo in the upper-right corner for a larger view.

I found a more dramatic view of Ron's antenna at  At the upper left click on "Aerial,"
then select "Bird's Eye" in the drop-down.  Ron's QTH is the seventh
house south of River Ridge Drive on the east side of Boxwood Lane.
Now click on the plus sign in the upper left to zoom in, and see the
antenna clearly.  By clicking on E, W or S on the compass rose in
the upper left, you can get completely different views of his
location.  It is a relatively big antenna on a modest sized
residential lot.

David Moore sent in an item from the National Science Foundation
that mentions lower levels of ultraviolet radiation from the Sun and
the effect on the outer atmosphere. Read it at,

The Autumnal Equinox is on September 23 this year.  This is a great
time for HF propagation, and this year we will probably see higher
levels of sunspot activity compared to the equinox in 2009.  Running
comparative studies on W6ELprop between average sunspot number of 5
and a more optimistic 25 for this year shows improvement from last
year's propagation.

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 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

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Sunspot numbers for August 26 through September 1 were 23, 11, 11,
25, 28, 27, and 51 with a mean of 25.4. 10.7 cm flux was 73.4, 73.2,
71.9, 73.9, 75, 74.6 and 76.3 with a mean of 74 Estimated planetary
A indices were 11, 14, 7, 2, 2, 2 and 4 with a mean of 6. Estimated
mid-latitude A indices were 11, 10, 5, 2, 0, 2 and 3 with a mean of