ARRL Propagation Bulletin ARLP041 (2007)

ARLP041 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 41  ARLP041
From Tad Cook, K7RA
Seattle, WA  October 5, 2007
To all radio amateurs 

ARLP041 Propagation de K7RA

We are on the road this week in Port Moody, British Columbia.

Sunspots reappeared, but only briefly.  In fact, it was one sunspot,
number 971, emerging September 28 for just a few days.  This after
21 days of no sunspots.  Now we are back into a zero-sunspot period
of indeterminate length, just four days so far.

Solar wind provided geomagnetic disturbances.  September 29 was the
most disturbed day.  There was another rise in activity centered on
October 3.

Currently the Air Force predicts a moderate rise in geomagnetic
activity peaking October 20 with a planetary A index of 15, and a
much larger rise to planetary A index of 25 on October 26.  But reports another solar wind stream to arrive
on or around October 11.  Geophysical Institute Prague predicts
quiet conditions October 5-7, unsettled October 8, quiet to
unsettled October 9, quiet October 10, and quiet to unsettled
October 11.

With September over, it is time to look at some averages.

Monthly averages of daily sunspot numbers for April 2006 through
September 2007 were 55.2, 39.6, 24.4, 22.6, 22.8, 25.2, 14.7, 31.5,
22.2, 28.2, 17.3, 9.8, 6.9, 19.8, 20.7, 15.6, 9.9 and 4.8.  Monthly
averages of daily solar flux for the same period were 88.9, 80.9,
76.5, 75.8, 79, 77.8, 74.3, 86.3, 84.4, 83.5, 77.7, 72.2, 72.4,
74.4, 73.7, 71.6, 69.2 and 67.

The average solar flux and sunspot numbers for September were the
lowest on this side of cycle 23.  This suggests we are still in the
cycle bottom, or perhaps haven't reached it yet.

But how low is 4.8 for a monthly average of sunspot numbers,
compared to the last cycle minimum?  Average monthly sunspot numbers
for October 1995 through August 1997 were 31.6, 15.3, 16.7, 18, 9.1,
12.1, 8.5, 11.9, 18.8, 13.2, 20.7, 2.9, 2.3, 20.6, 15.1, 8.7, 11.4,
13.7, 24.5, 29.6, 22.1, 17, and 36.1.  You can see that we are the
closest to September and October of 1996 (2.9 and 2.3), which had
some very long strings of no-sunspot days, the longest being
September 13 to October 20, 1996.

Here is the latest update on the 3-month moving average of daily
sunspot numbers:

Sep 05 39.3 
Oct 05 28 
Nov 05 35.3 
Dec 05 40.6 
Jan 06 32.4 
Feb 06 18.1 
Mar 06 27.7 
Apr 06 38.5 
May 06 39.7 
Jun 06 28.9 
Jul 06 23.3 
Aug 06 23.5 
Sep 06 21.2 
Oct 06 24.1 
Nov 06 23.1 
Dec 06 27.3 
Jan 07 22.7
Feb 07 18.5 
Mar 07 11.2 
Apr 07 12.2 
May 07 15.8 
Jun 07 18.7 
Jul 07 15.4 
Aug 07 10.2

The average for July, August and September, centered on August, at
10.2 is the lowest yet for this side of cycle 23.  This number was
derived by adding together all the daily sunspot numbers for those
three months, then dividing the sum by the number of days, which was

The past few months correlate pretty well with the fall of 1996,
when the 3-month moving average for July through November was 17.5,
12.4, 8.7, 10.1 and 14.2, observing that the August 2007 moving
average is similar to September or October 1996.

This week brought more email about mobiles working 3B7C.  Jim
Henderson, KF7E of Queen Creek, Arizona with 100 watts and a whip on
his Jeep, worked them on 17, 20, 30, and 40 meters.  Jim thought 40
meters would be the toughest, but to work them on 30 he rose at
1230z every morning for two weeks to check for a long path opening,
and again around 0030-0230 for short path.  Jim wrote, ''At just
after 0000Z on the 24th, I had to dash to the store for something
needed for the dinner. As I backed out of the driveway, around 0020Z
and before the usual peak from 3B7C, they rose out of the noise. I
split and gave my call just a couple times, and was promptly
rewarded with the 'KF7E KF7E GE Jim 599 599 K'.  So that made 4
bands mobile, from the more difficult path from the southwest USA,
sunspot minimum, and an honest 90-100w''.  Jim mentioned that local
DXer Bob Myers, W1XT of Surprise, Arizona worked them on 30 and 40
with a ground mounted mobile antenna and several random length
radials, a stealth installation surrounded by a large cinder block

Another 3B7C report from Randy Shirbroun, ND0C of Worthington,
Minnesota: ''I was able to break the pile-ups to get them on both 20
meter SSB and CW on 15 Sep. using 5 and 3 watts respectively.  The
QS0s were 6 minutes apart: 2113z and 2119z.  The antenna is a 3 el
triband Yagi at 15 meters.  I never could snag them on 40 (using a
wire) although they were pretty strong several evenings (typically
from 2300Z to 0100Z).  I even heard them very faintly one day on 15
meters''.  Randy has 298 countries confirmed using QRP.

Randy said he's noticed in the past few years that sometimes 10
meters seems open, while 15 is not, typically with trans-equatorial
or E-layer propagation.  He wonders if this is due to activity
(possibly more people trying 10 meters) or something else?

I put this to Carl Luetzelschwab, K9LA, for a few ideas on what
might be going on.  The first is that ionospheric absorption is
inversely proportional to the frequency squared.  So it is possible
for 10 meters to open, but absorption high enough on 15 meters to
discourage operators on that band.

The second, ''There are times when a lower band requires a lower
elevation angle than the higher band.  This is opposite to what your
antenna system does with a tribander at a fixed height - as you go
lower in frequency, the main lobe of your antenna system becomes
higher in elevation angle.  This is in essence an elevation angle
mismatch between what the ionosphere dictates and your antenna

The third possibility is that sometimes trans-equatorial propagation
appears to be frequency sensitive.  He studied possible propagation
from Honduras to Argentina, and noted propagation could occur at all
elevation angles from 1-10 degrees.  But 15 meters showed
trans-equatorial propagation at only a few angles.  He writes, ''It
looks like 15 meters is more prone to multi-hop (and thus inherently
a lower signal level) due to more refraction at the lower frequency
(caused by the two enhanced regions of electron density on either
side of the geomagnetic equator that enable TE)''.

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

Sunspot numbers for September 27 through October 3 were 0, 15, 16,
17, 12, 0 and 0 with a mean of 8.6. 10.7 cm flux was 67.1, 67.2,
67.6, 65, 67.7, 66.4, and 67.3 with a mean of 66.9. Estimated
planetary A indices were 19, 21, 26, 12, 8, 9 and 18 with a mean of
16.1.  Estimated mid-latitude A indices were 10, 15, 24, 11, 7, 5
and 9, with a mean of 11.6.