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ARRL Propagation Bulletin ARLP050 (2008)

ARLP050 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 50  ARLP050
From Tad Cook, K7RA
Seattle, WA  December 1, 2008
To all radio amateurs 

ARLP050 Propagation de K7RA

Today's bulletin is going out on Monday instead of Friday, due to
last week's holiday.  The last Propagation Forecast Bulletin was
ARLP049, released on Wednesday, November 26.  Starting Friday,
December 5, we return to a regular Friday weekly bulletin schedule.

The average sunspot number for the month of November was 6.8, up
from 5.2 for October.  The three month sunspot number average ending
November 30 -- centered on October was 4.5 -- an increase from
August and September's 1.1 and 2.5.

Here are the 3-month averages of sunspot numbers since mid-2006.

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
Sep 07  5.4
Oct 07  3.0
Nov 07  6.9
Dec 07  8.1
Jan 08  8.5
Feb 08  8.4
Mar 08  8.4
Apr 08  8.9
May 08  5.0
Jun 08  3.7
Jul 08  2.0
Aug 08  1.1
Sep 08  2.5
Oct 08  4.5

It looks like we had a double minimum, ten months apart.

Currently there are no sunspots visible, and solar flux hangs around
68.  December 8-9 the predicted solar flux rises to 70.  Perhaps
then we will see the return of a region which spawned sunspots
during the last solar rotation.  Geomagnetic indices have been
quiet, but are expected to rise this Friday, December 5.  Planetary
A index for that day is predicted to be 15.

If you check the thrice-daily solar flux readings from the
observatory in Penticton, I found the data ending November 20.  The
updated data is now on the site,

A page which references this is at, From this page you can
access a table of monthly solar flux averages back through February
1947.  The number you want is the Observed Flux in the first column.

Over a week ago Randy Crews, W7TJ of Spokane, Washington, wrote,
"Reviewing my old logs and operating activity, the frustration many
of us HF aficionados feel is due to the extended period between the
end of Cycle 23 and the beginning of Cycle 24. I have been on the
air 44 years, and never have I seen a cycle with such a long
extended bottom. Usually the bottom is brief, maybe 6-9 Months of
low Sunspot numbers and Solar Flux Values in the Mid 60s.  The rise
and fall is and has historically been short. Looking back (depending
on where one measures) there is a very long and stretched bottom
spanning 1 1/2 to 2 years. Graphically instead of a "V" we have a
"U" with a long flat bottom. It would be nice to have a payback
similar to Cycle 19 for the dues we have all paid."

Randy refers to Cycle 19 -- the big one peaking in the late 1950s,
and it is true that the minimum prior to Cycle 19 was long and low.

Tree Tyree, N6TR of Boring, Oregon sent his thoughts on comments by
W5WVO in Propagation Forecast Bulletin ARLP048 and also an antenna
for next weekend's ARRL 160 Meter contest.

He writes, "Agree strongly with the concept of being a big station
on six meters can be done much easier than 20 meters.

"A couple of points: E-skip is often high angle and an antenna on
six at 30 feet is VERY competitive.  When I worked Europe during the
June VHF contest, my 45 foot antenna was better than the one I had
at 95 feet.

"If someone has a modest tower, say a tribander on a 60 foot tower,
they actually have a very competitive antenna system for 160 meters
staring them in the face.  I recently took a 55 foot tower at N6TW's
QTH in Silverton, Oregon, which had a Force-12 40-10 meter beam on
it, and with about two hours of work, turned it into an antenna that
enabled QSOs with Europe and Japan, even without a kilowatt.

"As it turns out, towers in the 55-80 foot range with a beam acting
as a top hat turn out to be very close to a quarter wavelength.
Gamma matching this is pretty straight forward.  I typically use
some old coax as the gamma wire, suspended about 18-24 inches from
the tower, going up perhaps two-thirds of the way.  You can get good
performance with as few as 8 ground wires (the longer the better,
but there is no magic length. The wires are detuned when you lay
them on the ground).

"Use a variable cap to see if your gamma is working, and if you can,
use a transmitter as your SWR meter (AM broadcast stations often
interfere with the readings you see using an SWR meter).  Don't be
surprised if you see a pretty broad SWR curve.

I think Tree means to tune the gamma match with the variable
capacitor for best transmitter output, or "maximum smoke," as it is
sometimes called.  Find details on this kind of feed system for 160
meters at,,, and

Tree continues, "This is basically the antenna I have used for 20
years now to work over 200 countries on 160 meters. Certainly it
isn't the best choice for a receive antenna, but if you are in a
quiet QTH you would be surprised at what you can hear with good
conditions (which we are currently enjoying on Topband)."

An excellent weekend to test this would be the ARRL 160 Meter
contest next weekend, December 5-7.

See for
contest rules.

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 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

Instructions for starting or ending email distribution of this
bulletin are at

Sunspot numbers for November 20 through 26 were 0, 0, 0, 0, 0, 0,
and 0 with a mean of 0.  10.7 cm flux was 69.6, 68.5, 69, 69, 67.9,
67.7, and 68.3 with a mean of 68.6.  Estimated planetary A indices
were 2, 1, 1, 3, 0, 10 and 8 with a mean of 3.6.  Estimated
mid-latitude A indices were 1, 0, 0, 1, 2, 11 and 11 with a mean of


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