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ARRL Propagation Bulletin ARLP007 (2005)

ARLP007 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 7  ARLP007
From Tad Cook, K7RA
Seattle, WA  February 18, 2005
To all radio amateurs 

ARLP007 Propagation de K7RA

Conditions improved this week over last. The average daily sunspot
number rose nearly 34 points to 75.1, and the geomagnetic indices
were down over the week. The geomagnetic field may become more
active, and for February 18-20 the planetary A index is predicted at
20, 20 and 15. The major sunspot group affecting us this week will
soon move off the visible solar disk, but there is a small sunspot
group on the other side of the sun. Conditions should be fair to
good for the ARRL International DX CW Contest this weekend.

Carl Luetzelschwab, K9LA has an interesting and useful propagation
column in the March 2005 issue of WorldRadio. With ionosonde data he
demonstrates how daily variations in solar flux have little effect
on the MUF. Instead, propagation is better predicted with a smoothed
sunspot number applied to seasonal variations.

For instance, this afternoon when I wanted a feeling for when 15 and
17 meters would still be open toward various locations, it was
better to use W6ELprop with an average of sunspot numbers for the
previous five days rather than today's solar flux. You can get the
recent sunspot numbers from, and download
W6ELprop from

This afternoon I went out to the car to do some 17 meter mobile
work. Geomagnetic indices were low and the band was good. I had a
nice CW chat with KG0TS in Des Moines, Iowa, and then worked
9Y4/YL2GM in Tobago on SSB. Juris was in the Caribbean getting ready
for the DX contest from 9Y4W this weekend.

If you would like to comment or have a tip, email the author at,

For more information concerning propagation and an explanation of
the numbers used in this bulletin see the ARRL Technical Information
Service propagation page at,

Sunspot numbers for February 10 through 16 were 63, 73, 72, 73, 115,
69 and 61 with a mean of 75.1. 10.7 cm flux was 114.1, 114.1, 116.4,
115.5, 118.1, 121.7 and 112.8, with a mean of 116.1.  Estimated
planetary A indices were 17, 11, 5, 4, 5, 5 and 13 with a mean of
8.6. Estimated mid-latitude A indices were 11, 7, 3, 2, 4, 1 and 8,
with a mean of 5.1.


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