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ARRL Propagation Bulletin ARLP047 (2008)

ARLP047 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 47  ARLP047
From Tad Cook, K7RA
Seattle, WA  November 14, 2008
To all radio amateurs 

ARLP047 Propagation de K7RA

We soon may be talking about a day or two without sunspots as the
norm, perhaps when looking at a preceding month -- quite the
opposite of noting the few days with sunspots. It seems like a long
time ago because of the long strings of spotless days. We saw eight
days in a row with visible sunspots around mid-October, followed by
another eight days around the start of November, then after just
three days of no spots. By the end of today -- Friday, November 14
-- we may see five straight days, possibly followed by more.

We have to look at last year to find long periods without spotless
days. From June 25, 2007 until July 19, 2007, there were 25 days
with sunspots that were continuously visible. From April 25, 2007
until May 23, 2007, there were 29 days with spots; from December 30,
2006 until February 10, 2007, there were 43 days with spots. This
makes January 2007 the last time we observed a calendar month with
no spotless days.

Why are sunspots important?  They correlate with a reflective or
refracting ionosphere.  Here is a nice picture from University of
Iowa illustrating the earth with ionosphere:

Another one, from G4NSJ, shows a very basic diagram of a shortwave
radio signal traveling a great distance via the ionosphere:

There are variations influenced by time of day, season and location,
but generally the higher the sunspot number, the higher the
frequency that can be used for communication. This is important,
because when you double the frequency you are operating on (for
instance, from 20 to 10 meters), the relative size of your antenna
can be cut in half to still have the same efficiency. So, with
enough solar activity, you could communicate around the world on 10
meters with a highly efficient directional antenna that is much
smaller and easier to construct than an equally efficient 20 meter
antenna. At the higher frequencies, there is also less absorption of
higher frequency shortwave signals.

There is a critical number called MUF (Maximum Usable Frequency)
that can be calculated based on the factors mentioned above: time of
day, time of the year, the two locations trying to communicate and
the level of solar activity.  For radio waves at a frequency above
the MUF, they can just pass on through the ionosphere, never to be
heard again.

For calculating conditions based on these factors, check the
reference to the same W6ELprop program mentioned in last week's
Propagation Forecast Bulletin ARLP046 at,  Check out the other
references on the same K9LA web page, which are excellent.

The ARRL SSB Sweepstakes Contest is this weekend. With the recent
sunspot activity, conditions should be better on 15 meters than they
would be without sunspots. For example: California to Ohio. If there
had been no sunspots leading up to the contest weekend, 15 meters
looks rough, but could open from 1800-1930z, perhaps as early as
1600 to as late as 2100z. But with recent sunspots, a great opening
from 1630-2100z is likely and could start an hour earlier and end 30
minutes to an hour later.

Over that path and over this weekend, with no sunspots the MUF would
rise above 20 MHz at 1730-2000z, peaking around 20.6 MHz at 1830z.
But with sunspots over a few days, the MUF is likely to go above 21
MHz from 1630-2100z, peaking at 23.7 MHz around 1830z.

On 20 meters with no sunspots, the path looks good 1430-1530z and
1800-1830z.  With sunspots 20 meters looks good 1430-1500z, and
excellent 1600-2000z.

40 meters is good over the path day and night, sunspots or none.
Strongest signals are from when the Sun sets around 0047z in
California to within the hour after the Sun rises in Ohio around

Jeff Hartley, N8II of Shepherdstown, West Virginia wrote to us last
week about the CQ Worldwide DX Phone Contest, October 25-26.

Jeff wrote, "I operated the CQWW single band on 15M and the band was
poor compared to most years, probably about the same as in 2007. The
skip zone was long enough that I didn't work several active northern
Caribbean countries until mid-afternoon Sunday. There appeared to be
sporadic E to VE1/VY2 and VE3 Saturday morning and to VP5/VP9/C6 on
Sunday. The closest F2 contact to my south was KP2M. There was
decent propagation to very southern EU both days. I caught VU7SJ
(loud) about the same time as the Es around 1400Z Saturday and
VU2PAI (weak) called in Sunday around 1600Z for my best polar
opening DX."

He continues, "It was possible to work about 30 zones on 15M from
the USA. From 1245-1355Z Sunday there was a big opening with S9+ EU
signals about as far as Lithuania. 3 Russians UA3 and UA6 were
worked and one UR. 5R8FU was loud Sunday afternoon with a huge
pile-up; all of Africa was workable, but zones 34 (missed), 36, 37
and 39 were pretty rare. Best Pacific DX was AH0 around 23Z Sunday."

He goes on to say, "40M and 30M seem to be staying open to EU quite
late (after my sunset 30M, thru 0200Z 40M) some days which is

Owen Duffy, VK1OD of Ainslie, near Canberra in Southeast Australia,
sent in a link to a chart he made of spotless days around the solar
cycle transition.  See it at, Also check out the rest of
his site at,

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 6 through 12 were 11, 0, 0, 0, 16, 18,
and 21 with a mean of 9.4.  10.7 cm flux was 68.6, 67.8, 68.3, 68.4,
69.3, 71.4, and 70.9 with a mean of 69.2.  Estimated planetary A
indices were 1, 8, 14, 12, 3, 1 and 2 with a mean of 5.9.  Estimated
mid-latitude A indices were 0, 7, 11, 10, 3, 1 and 4 with a mean of


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