Register Account

Login Help

ARRL Propagation Bulletin ARLP042 (2006)

ARLP042 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 42  ARLP042
From Tad Cook, K7RA
Seattle, WA  October 13, 2006
To all radio amateurs 

ARLP042 Propagation de K7RA

From on the road in Eastern Washington this morning, here is the
weekly Propagation Bulletin.

Last week's bulletin (ARLP041) reported the week's solar flux and
sunspot numbers rose slightly, and this week they declined. Average
daily sunspot numbers were about half, sinking from 34.6 to 16.9.
Wednesday and Thursday of this week had 0 sunspots, and likely we'll
see more of no spots as the solar cycle continues its decline.

Geomagnetic conditions were very stable, with an average
mid-latitude A index of 3.1, about half the previous week's number.
We may see some unsettled to active conditions on Sunday, October
15, when the planetary A index is predicted at 20. The same number
may come up around October 21 and again on October 28.

Last week's bulletin mentioned the California QSO Party, and Kevin
Rowett, WB6S of Cupertino, California sent in a very interesting
link comparing activity in the 2006 contest with the 2005 event.
See it yourself at,

Note there are links on the left side of the page comparing activity
on different bands. If you click on the 15 meter link, you'll see
that this year on the first day of the event the QSO rate was much
higher than last year, but last year there was a large peak of
activity around 1900z on the second day. Also, this year the 15
meter activity constituted a much larger portion of the total
reported QSOs. The remaining bands track pretty closely from year to

Dan Ferguson, K4VOA of Little River, South Carolina corrected our
description in last week's bulletin of smoothed sunspot numbers, and
how they are derived.

The smoothed sunspot number can't ever be calculated for the current
date. Because it needs data six months before and six months after
any month to calculate the smoothed sunspot number for that month,
it is always at least six months behind the current date.

To calculate the smoothed sunspot number for March 2006, you need
the monthly averages of daily sunspot numbers for each of the months
from September 2005 through September 2006. You take half the value
of the September 2005 average, add it to half the value of the
September 2006 average, then add it to the full value of each of the
intervening 11 months. Take this total and divide by 12, and that is
your smoothed sunspot number for March 2006. You cannot know the
April 2006 smoothed sunspot number until the last day of October

The procedure is described on a web page from the National
Geophysical Data Center, located at,

For this week, expect more of the same with little or no sunspots.
This means the higher bands, such as 15, 12 and 10 meters, won't be
as promising as a few years ago. But on this Friday the Thirteenth,
we can look forward to October 2007, when the sunspot count by many
estimates will be higher than it is now, and climbing too.

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 October 5 through 11 were 27, 23, 24, 22, 11, 11
and 0 with a mean of 16.9. 10.7 cm flux was 77.3, 76.4, 76.5, 75.2,
75, 75.3, and 73.6, with a mean of 75.6. Estimated planetary A
indices were 3, 3, 9, 7, 5, 2 and 3 with a mean of 4.6. Estimated
mid-latitude A indices were 2, 2, 7, 6, 3, 0 and 2, with a mean of


Instragram     Facebook     Twitter     YouTube     LinkedIn