ARRL

ARRL Propagation Bulletin ARLP020 (2008)

SB PROP @ ARL $ARLP020
ARLP020 Propagation de K7RA

ZCZC AP20
QST de W1AW  
Propagation Forecast Bulletin 20  ARLP020
From Tad Cook, K7RA
Seattle, WA  May 9, 2008
To all radio amateurs 

SB PROP ARL ARLP020
ARLP020 Propagation de K7RA

Again this week Earth residents saw a new, but brief sunspot from
new Cycle 24, judging from the polarity of the spot, sunspot 993.
This one was south of the solar equator, so it has the same polarity
as any Cycle 23 spot that was north of the equator.  After two days
it was gone, not from drifting over the edge of the visible solar
disk, it just disappeared.

Geomagnetic indices were mostly quiet this week, except for some
only slightly unsettled planetary A index numbers for May 2-3.  The
next active geomagnetic period is expected May 20, with a planetary
A index of 25.  For May 9-15 the predicted planetary A index is 8,
5, 5, 5, 12, 8 and 5.

For May 9-15 Geophysical Institute Prague predicts quiet conditions
May 9, quiet to unsettled May 10, unsettled May 11-13, quiet to
unsettled May 14, and quiet again on May 15.

An email from Martin McCormick, WB5AGZ of Stillwater, Oklahoma
mentioned sporadic-E propagation and meteor showers.  Last Saturday,
May 3 he tuned to the Channel 2 television frequency centered on
55.25 MHz with his receiver set to CW mode, upper sideband.  The
closest Channel 2 station is 50 miles from him in Tulsa, so that
makes spotting on this frequency possible, because locally from his
position it is quiet.

He quickly heard a ping, then another, then a very loud ping with
the slide-whistle effect associated with Doppler shift.  This was
from the Eta Aquarids meteor shower, which peaked two days later on
May 5.  The Eta Aquarids occur when Earth passes through dust left
behind from Halley's Comet.

Martin noted that on February 17, 2009 when analog television goes
dark we will lose a large group of powerful beacon stations for the
low VHF spectrum, useful for detecting 6 meter openings.  There are
about 50 active broadcasters on Channel 2 in the United States, I
assume most operating around the clock.  So for the sporadic-E
seasons we only have this Summer remaining to use this tool, and the
shorter sporadic-E Winter season.  After that, all quiet.  I don't
know what will eventually replace television broadcasting in the
spectrum just above our 6 meter band when television channels are
refarmed.

Last week's Propagation Forecast Bulletin ARLP019 mentioned
locations of magnetometers such as the Boulder and Fredericksburg
monitoring stations, which are used to generate separate
mid-latitude K and A indices.  I've wondered if these same
geomagnetic indicators were generated for other stations, such as
the one at Newport, Washington, close to the Idaho border.

Steve Lybarger, NU7T of Sparks, Nevada sent a link showing seven
hourly K index readings from nine magnetometers, most in North
America.  See it at,
http://www.swpc.noaa.gov/ftpdir/forecasts/MA/MAhr.txt.  The
locations of most stations were shown in last week's bulletin with
the link, http://geomag.usgs.gov/observatories/, and for Meanook,
Ottawa and St. Johns, check,
http://gsc.nrcan.gc.ca/geomag/obs/obsmap_e.php for National
Resources Canada information.  For Hartland, which is in Southwest
England, check,
http://www.dcs.lancs.ac.uk/iono/cgi-bin/magnetometers.

Note that on the NOAA site listed above, not only does it show a new
K index every hour, but an hourly planetary A index based on the
planetary K index for the past 3 and 24 hours, but updated every
hour.

Each of the three countries has a slightly different method of
showing location coordinates.  The United Kingdom uses the standard
system that most of us are accustomed to, rather than the rather
arcane scheme outlined last week for USGS sites.  The Canadian
method seems to combine both, using standard figures for latitude,
but longitude extending to 360 degrees.  So for locating Canadian
magnetometers, use their stated latitude under geographic
coordinates, but subtract their stated longitude from 360 to obtain
west longitude.

When comparing geomagnetic data, we are mostly interested in
latitude, because during active geomagnetic periods the activity is
more intense at higher latitudes.

Note that from the Canadian site, you can scroll down to get the
3-hour geomagnetic K index for Ottawa, Victoria and Meanook.

Last week's bulletin promised to go over some simple methods for
finding the best times and frequencies that are likely to produce
good propagation from your location to any other.  This uses the
free program W6ELprop, available from, http://www.qsl.net/w6elprop/.
You can find past bulletins which outline uses for the program at,
http://tinyurl.com/57zlwl.

The program uses predicted smoothed sunspot numbers to show the user
propagation paths that are most likely.  I have been advised that
these sorts of programs do not produce better results by using
today's actual solar flux or sunspot number.  Rather, it calculates
MUF (Maximum Usable Frequency) based on predicted smoothed sunspot
number, designed so that about half the time the actual MUF is above
the predicted MUF, and half the time below.  Remember that MUF is
calculated for a specific path between two specific points on the
globe at a particular time and season (based on date).

You can usually find the current predicted smoothed sunspot number
updated monthly in the Preliminary Report and Forecast from,
http://www.swpc.noaa.gov/weekly/index.html.  For instance, this
week's issue at http://www.swpc.noaa.gov/weekly/pdf/prf1705.pdf on
page 9 shows May 2008 predicted smoothed sunspot number as either 5
or 6, based on a lack of consensus among panel members who predict
the next solar cycle.  So use either number or 5.5 if you wish.

If you want to use a sunspot number that more closely reflects
recent activity, you can average the latest three sunspot number
readings from http://www.swpc.noaa.gov/ftpdir/indices/DSD.txt.  So
for today, I would use a sunspot number of 0.  If it was May 6, and
the table only showed data through May 5, I would use an average of
9.3.  You can set up W6ELprop to default to either solar flux or
sunspot number entries.  If you want to change at any time, or
insure your intended figures are used, precede the number with the
letter S for sunspot number, or F for flux.

You can also change or add frequencies to the predictions, for WARC
bands, shortwave listening, or the relatively new 60 meter band.
Users can add atlas info to add target locations.  What you end up
with are some possible signal levels and ratings for each half hour.
The A designator means the path is likely to be available close to
100 percent of the time, and of course higher signal levels are
good.  If you want to add the latest K index, you can get it from
NOAA at http://www.swpc.noaa.gov/ftpdir/indices/DGD.txt.

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 web page 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/.

Instructions for starting or ending email distribution of this
bulletin are at http://www.arrl.org/w1aw.html#email.

Sunspot numbers for May 1 through 7 were 0, 0, 0, 13, 15, 0, and 0
with a mean of 4.  10.7 cm flux was 68.5, 68.1, 67.3, 68.3, 67.6,
67.2, and 66.5 with a mean of 67.6.  Estimated planetary A indices
were 9, 12, 12, 8, 11, 10 and 4 with a mean of 9.4.  Estimated
mid-latitude A indices were 6, 7, 9, 6, 8, 9 and 5, with a mean of
7.1.
NNNN
/EX