ARRL Propagation Bulletin ARLP038 (2006)

ARLP038 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 38  ARLP038
From Tad Cook, K7RA
Seattle, WA  September 15, 2006
To all radio amateurs 

ARLP038 Propagation de K7RA

The Autumnal Equinox for the Northern Hemisphere will occur on
September 23 this year (at 0402z). We've been moving from summertime
propagation conditions to fall, which is generally a better time for
HF propagation, except for the lack of sporadic-E skip.

On 20 meters, instead of intercontinental openings into the evening,
we see improved conditions well before dark. For instance, comparing
projected conditions for this weekend from the East Coast USA to
Europe, with conditions in early July, 20 meters was marginal during
the morning and mid-day, but became better late in the day.
Conditions between Pennsylvania and Germany around July 5 show a
projected jump in signal levels around 2200z, then excellent
propagation until around 0700z.

But for mid-September 20 meters over the same path has rising
signals from morning until early evening, with signals dropping
after 2300z. 17 meters over the same path looks very good this
weekend from 1230z until 2130z, but for early July the chances of a
good path were much lower, except for a brief period around

Average daily sunspot numbers rose over the past week by 19 points
to 44.3. Geomagnetic conditions were quiet every day. For the next
week Geophysical Institute Prague predicts quiet conditions for
today, September 15, then quiet to unsettled on the 16th, unsettled
geomagnetic activity on the 17th and 18th, then quiet on September
19-21. The U.S. Air Force spaceweather operation predicts planetary
A index (a measure of geomagnetic activity) for September 15-21 at
5, 10, 12, 15, 8, 5 and 5.

Steve Hammer, K6SGH of Santa Barbara, California wrote asking about
a source for an archive of daily sunspot numbers that he might
import into a spreadsheet. Al Woodhull, N1AW of Amherst,
Massachusetts had a similar request. One handy source for this,
which is easy to update using this bulletin, is the free Solar Data
Plotting software from Scott Craig, WA4TTK. The program stores the
daily sunspot number and solar flux going back to the late 1980s in
a file called graph.dat.

Scott's program is at,, and
there is also a separate update to the data file with numbers up
through the end of August. You can update the file
semi-automatically by saving this weekly bulletin in a plain-text
file, then using the software to read the file and suck up the data.
To bring the current file up to date would only require a file made
from this bulletin and another from last week's edition.

Al and Steve, mentioned in the previous paragraph, each have their
own websites highlighting some of their interesting activities. See
Steve's at,, and don't miss his Moxon Antenna
site at, Al's website is,

Gary Nixon, WA6HZT of Fair Oaks, California and Andy Gudas, N7TP of
Amargosa Valley, Nevada both sent in references to an article
claiming that thunderstorms actually affect the ionosphere and radio
propagation (other than causing QRN, of course). Read it at,

Dick Bingham, W7WKR of Stehekin, Washington sent in a quote
concerning 160 meters from Wolf Ostwald, DF2PY. Wolf write, "This
years West Coast window opened about 3 weeks earlier than in the
last years. K7RL and W1YY/7 made it into EU today about 45 min and
25 min prior to local sunrise. Their sigs were fantastic for topband
standards, even good enough for 'ragchewing.' I take this as a good
omen for the new season and it repeatedly shows again the
superiority of the CW mode to master difficult paths under any

And finally, Bill Isakson, AC6QV of El Cerrito, California wrote
this about 17 meters. He writes, "I thought, since you just now
indicated a software result that not much should happen above 20
meters, that I should tell you that 17 meter activity has been great
recently. Earlier this week I had QSO with a station in San
Francisco, Argentina from here in Berkeley near San Francisco,
California, for example, on my way home from work around 5 PM, that
is, mobile on a Hamstick."

Bill continues, "His S9 CW signals were mildly strong and clean in
this electrically noisy environment, though mine at his end were
weak (559 he said, but I had to make several repeats, so it was
probably 539). I would give you his call sign, but my email is
nowhere near my logbook. I can say he was a powerhouse station. The
17 meter band has generally been open most of the afternoons here
and I have heard VK land as well. The radio I am using for mobile
does not have any special filtering in use either, so CW and USB
have been through the same set of wide filters."

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 September 7 through 13 were 39, 49, 51, 50, 42,
41 and 38 with a mean of 44.3. 10.7 cm flux was 86.7, 87.2, 85.5,
87.3, 84.6, 84.1, and 82.9, with a mean of 85.5. Estimated planetary
A indices were 8, 4, 2, 6, 8, 4 and 6 with a mean of 5.4. Estimated
mid-latitude A indices were 5, 4, 1, 5, 7, 2 and 3, with a mean of