ARRL Propagation Bulletin ARLP032 (2006)

ARLP032 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 32  ARLP032
From Tad Cook, K7RA
Seattle, WA  August 11, 2006
To all radio amateurs 

ARLP032 Propagation de K7RA

On four days this week the sun was spotless, so the average daily
sunspot number for the week dropped over 11 points to 8.6.  Sunspot
numbers are now recovering and climbing, from zero on Monday to 12,
25 and 37 on Tuesday through Thursday.  Sunspot numbers and solar
flux should continue a modest recovery through next week.  When the
sunspots were zero, the solar flux (a measurement of 10.7 GHz energy
from the sun, observed at a station in British Columbia) was below
70.  Now solar flux is expected to rise in the short term to 85 or

Rising sunspot numbers and solar flux mean higher MUF (Maximum
Usable Frequency), although not a lot higher.  For instance, using
propagation prediction software, for today with zero sunspots, the
MUF over the path from Philadelphia to Germany would go above 17 MHz
from 1430-2230z, to a maximum of 17.6 MHz.  But with an average
sunspot number of 40, the MUF over the same path rises above 19 MHz
from 1400-2230z, peaking at 19.8 MHz.  If the sunspot number were
120 instead, a figure we won't observe for a few years, the MUF
would rise above 23 MHz from 1430-2130z, peaking at 23.8 MHz.  The
difference on those three scenarios would be whether 20 meters, 17
meters, or 15 meters is the highest practical band to use.

With existing conditions as they are, that path to Germany would be
best on 17 meters from 1230-0000z, with stronger signals toward the
end of that period, but the best chances for an opening around
1730-2100z.  20 meters should have slightly stronger signals, with
openings beginning weakly around 1130z and signals gradually
increasing to 0200z, and the signals falling off afterward.  Best
bet would be 2130-0100z on 20 meters.

Compared to a month ago, operators at each end of that path would
notice a much stronger chance of a 17-meter opening, and a much
earlier closing of 20 meters, with the days getting shorter as we
move toward the fall equinox.

Similarly, a month's difference on the West Coast to Japan path
would see the rise of 15 meters as a viable choice from 2130-0200z.
Moving toward fall, 20 and 17 meters would close a little earlier,
while 30 and 40 meters would each open about an hour or more

Steve Rasmussen, N0WY of Plattsmouth, Nebraska is the contest
manager for 10-10 International (see and he
says ten meters had great openings after sunrise and after dusk
during the 10-10 contest last weekend.  He worked 151 stations,
mostly to the east and southeast. N2EOC (with an exceptional 10
meter antenna, says Steve, although he didn't say what N2EOC is
using) in New Jersey worked 255 stations.  Steve says, ''WN4AMO in
Florida did 259 and AH6RF in Hawaii made 184.  KK7UU in Oregon ended
up with 146.  The band is NOT dead. You just have to be there when
it is open.''

W4HLR, Howard Runions of Newbern, Tennessee says he got cards from
F8DBF and HI3TEJ for his 3 watt 50.115 MHz SSB contacts on July 17.
He is thrilled with the cards, naturally.

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 August 3 through 9 were 23, 0, 0, 0, 0, 12 and
25 with a mean of 8.6. 10.7 cm flux was 71.3, 69.6, 69.5, 69.5,
69.8, 71.4, and 74.1, with a mean of 70.7. Estimated planetary A
indices were 6, 3, 4, 4, 32, 12 and 9 with a mean of 10. Estimated
mid-latitude A indices were 5, 2, 2, 2, 19, 10 and 9, with a mean of