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ARRL Propagation Bulletin ARLP008 (2004)

ARLP008 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 8  ARLP008
From Tad Cook, K7RA
Seattle, WA  February 20, 2004
To all radio amateurs 

ARLP008 Propagation de K7RA

Average daily sunspot numbers were down a little this week (compared
to last week) and so were the daily solar flux numbers. The average
daily Planetary A index was slightly higher. Geomagnetic indices
settled down this week on February 16-19 to yield some nice
conditions on HF. There weren't many sunspots, so the MUF wasn't as
high as several years ago, but the quiet conditions are a nice
respite from the stormy geomagnetic conditions of late.

The quiet conditions should continue though this weekend, which is
good news for contesters who will participate in the ARRL
International DX CW Contest. The predicted Planetary A index for
Friday through Monday, February 20-23 is 10, 10, 12 and 12. Solar
flux is expected to stay below 100 until around Leap Year Day,
February 29.

Carl Luetzelschwab, K9LA has an interesting article in the March
issue of "WorldRadio" about low band propagation during the solar
minimum. He tested the theory that 160-meters is better during the
low part of the solar cycle, and proposes that what helps the lower
frequencies is not really an absence of sunspots, but quieter
geomagnetic conditions.

Because solar activity is lower during the years around the solar
minimum, there is less chance of flares or coronal holes upsetting
the geomagnetic field. A disturbed geomagnetic field can severely
affect signals passing through high latitudes.

He found that stations situated where they can propagate signals to
their destination without passing through the high latitude auroral
zone may have a great advantage during periods of greater solar

For instance, K9LA's path to Europe is a polar path, and so he is
affected by polar absorption when the K index is high. He compared
notes with W8JI in Georgia, whose paths to most major ham
populations stays outside the auroral zone, and the Georgia station
can work much more 160-meter DX during the cycle peak than K9LA can.

For more information concerning propagation and an explanation of
the numbers used in this bulletin see the Propagation page on the
ARRL Web site at

Sunspot numbers for February 12 through 18 were 65, 71, 64, 75, 81,
22 and 23 with a mean of 57.3. 10.7 cm flux was 112.2, 107.8, 103.7,
102.1, 98.7, 101.9 and 97.7, with a mean of 103.4. Estimated
planetary A indices were 28, 21, 18, 18, 7, 5 and 8, with a mean of


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