ARRL

ARRL Propagation Bulletin ARLP035 (2007)

SB PROP @ ARL $ARLP035
ARLP035 Propagation de K7RA

ZCZC AP35
QST de W1AW  
Propagation Forecast Bulletin 35  ARLP035
From Tad Cook, K7RA
Seattle, WA  August 24, 2007
To all radio amateurs 

SB PROP ARL ARLP035
ARLP035 Propagation de K7RA

Conditions were quiet this week, with no geomagnetic disturbances
and most days had zero sunspots.  For the past two days, August
22-23, the sunspot number was 11 and 12, indicative of a single
sunspot group.

Slightly unsettled conditions are expected this weekend, with a
planetary A index from August 24-30 expected at 8, 15, 15, 12, 8, 8
and 5.  Sunspot activity is expected to remain low, as lone sunspot
969 moves across the sun.

Geophysical Institute Prague predicts quiet conditions for August
24, unsettled August 25, quiet to unsettled August 26, quiet August
27, unsettled August 28, and quiet again August 29-30.

Back in ARLP032 dated August 3, this bulletin said if the average
sunspot number for August is above 20, then we will see another rise
in our three-month moving average, which was also shown in that
issue.  Instead, for the three weeks and two days of this month
we've had eight days of no sunspots, and the average sunspot number
for the month thus far is 8.7.  So perhaps early this spring was not
the sunspot cycle minimum.  Note the average sunspot numbers for
March and April of this year were 9.8 and 6.9.  Monthly averages
seemed to be rising, until now.

Jerry Reimer, KK5CA wrote to us recently about NVIS propagation
(Near Vertical Incidence Skywave, or high angle radiation for local
or regional coverage).  In his email, he wrote, ''NVIS experimenters
and practitioners would do well to always consider the foF2 and fMUF
values, available here:
http://www.sec.noaa.gov/ftpmenu/lists/iono_day.html.  For most of
the U.S., 40m is currently well above what is usable for NVIS
propagation. Sometimes 60m is not usable, and this can sometimes
also include 75/80m for some areas.  Many people are confused when
their low ''NVIS'' antenna (often a resonant horizontal wire dipole
at 6-20 feet) is ineffective for high angle propagation above the
fMUF, while it is effective in working stations over 200 miles away.
Most of these antennas radiate signals at all angles, not just the
highest angles, and the lower angle signals are refracted with more
favorable S/N ratios than are the vertical signals, which pass
through the F-layer.  For reliable NVIS propagation, it is critical
to select a frequency which is 50-80 percent below the fMUF''.

In that list that Jerry referenced, there are isosonde stations in
North America, one of which may be local to you.  Each page lists a
latitude and longitude, but the format may be unfamiliar.  They use
an odd longitude reading that goes from zero degrees on the prime
meridian east, covering the full 360 degrees.  So if the number is
E359, that would be one degree west of the meridian.  For these
stations in North America, just subtract the number shown from 360
to get the approximate location of the ionospheric sounding.  For
Dyess, it shows the location as N32E260.  This would be 32 degrees
north latitude, 100 degrees west longitude, because 360 minus 260 is
100.

Locations you might check, shown with the states they are in, are
Millstone Hill (MA), Point Arguello (CA), Boulder (CO), Bear Lake
(UT), Wallops (VA), Eglin (FL) and Dyess (TX).

The critical frequency you are looking for is in the foF2 column.
An interesting article about ionosondes is at
http://www.prc68.com/I/MWI.shtml.

Another list of stations is
http://www.ngdc.noaa.gov/stp/IONO/StationP12.html, but I don't know
where to get data from these.

David Moore sent a link to an article about Japan's solar research
satellite, Hinode:
http://www.esa.int/esaSC/SEMKOOWZK5F_index_0.html.

If you would like to make a comment or have a tip for our readers,
email the author at, k7ra@arrl.net.

For more information concerning radio propagation, see the ARRL
Technical Information Service at
http://www.arrl.org/tis/info/propagation.html. For a detailed
explanation of the numbers used in this bulletin, see
http://www.arrl.org/tis/info/k9la-prop.html. An archive of past
propagation bulletins is at http://www.arrl.org/w1aw/prop/ . Monthly
propagation charts between four USA regions and twelve overseas
locations are at http://www.arrl.org/qst/propcharts/.

Sunspot numbers for August 16 through 22 were 0, 0, 0, 0, 0, 11 and
12 with a mean of 3.3. 10.7 cm flux was 67.3, 67.6, 67.9, 67.8,
69.1, 69.3, and 70, with a mean of 68.4. Estimated planetary A
indices were 7, 5, 4, 3, 2, 4 and 4 with a mean of 4.1. Estimated
mid-latitude A indices were 6, 2, 1, 2, 2, 3 and 2, with a mean of
2.6.
NNNN
/EX