ARRL Propagation Bulletin ARLP007 (2009)

ARLP007 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 7  ARLP007
From Tad Cook, K7RA
Seattle, WA  February 13, 2009
To all radio amateurs 

ARLP007 Propagation de K7RA

Sunspots returned this week, or one did, but it is an old Cycle 23
spot.  Sunspot 1012 has been visible the last couple of days,
February 11-12.  It is down near the Sun's equator, which is typical
for spots from a previous cycle.  Nice to have a sunspot, but it
doesn't indicate activity from the new Cycle 24, which has been so
eerily quiet.

We saw a few days this week when the geomagnetic activity was very,
very low.  Look at
and note all the zeroes from February 8-10 in both the middle
latitude and high latitude numbers.

We could see some geomagnetic activity this weekend due to energy
from a solar wind stream.  The predicted planetary A index from NOAA
for February 13-19 is 5, 10, 15, 10, 5, 5 and 5.  Geophysical
Institute Prague sees slightly earlier activity, with quiet on
February 13, unsettled February 14, quiet to unsettled February 15,
and quiet February 16-19.

If we get at least a few days that have a sunspot number of 11 (this
is the minimum non-zero sunspot number), it makes a difference in
the MUF of many paths.  For instance, with no sunspots, the
projected path from Philadelphia to France for today shows MUF
values every half hour from 1500-1900z as 17.7, 18.2, 18.5, 18.6,
18.5, 18.4, 17.4, 16.5 and 15.4 MHz.  With a sunspot number of 11
for several days, the MUF values change to 19.4, 20, 20.1, 20.1, 20,
19.5, 18.3, 17.3 and 16.2 MHz.

Over the same path, with no sunspots over the same time period the
odds of communication on 17 meters would be 25-50% at 1500z, 50-75%
at 1530-1730z, 25-50% at 1800z, and less than 25% at 1830-1900z.

With a sunspot number of 11 for several days, the same Philadelphia
to France path would have odds of success on 17 meters of 75-100%
from 1500-1700z, 50-75% at 1730-1800z, 25-50% at 1830z, and less
than 25% at 1900z.

Last week's Propagation Forecast Bulletin ARLP006 contained a
comment about 10-meter propagation, and that Great Britain used a
system operating from 30-50 MHz in the World War II era for
over-the-horizon radar, known as Chain Home.

This brought an interesting email from Brett Graham, VR2BG about
Chain Home, and later HF OTH radar systems.  Brett says Chain Home
operated on 20-30 MHz.  For images of Chain Home antenna towers,
look at,, and

You can watch an online video of Brett explaining the history of OTH
radar and modern uses at a multimedia messaging server at,
mms://  Just click on that link, or paste
it into your web browser's URL field without the usual http at the
front.  This was recorded at the 2008 Asia-Pacific DX Convention in
November in Osaka, Japan.

Many of us recall the Russian Woodpecker OTH system of past years,
and the huge amount of QRM it generated all over the HF spectrum.
Check out some photos of those systems at,,

I believe at least one of those images is from inside the Chernobyl
exclusion zone.  Brett comments on the video that it took a lot of
electrical power to drive those huge arrays.  On the video Brett
gives a great deal of information concerning current HF OTH systems
operated by different countries, and the type of threat they present
to HF communications.

Joe Schroeder, W9JUV of Glenview, Illinois sent this memory of Chain
Home signals after World War II:

"N6TP's comment on Chain Home radar really brought back memories! I
was a newly minted ham in 1946 and when 10 (the only HF band the
military had released for ham use!) opened to Europe in the fall we
used the Chain Home buzz on the high end of the band to judge band
conditions to Europe. I was using a home made two element Yagi roped
to the top of the chimney and 50 watts to an 807. When the FCC gave
us the 27 Mc band we'd sometimes work Europe duplex by calling CQ
continuously on 11 and announcing 'Tuning 28.3 to 28.4 for any

He continues, "My 807 and I had 52 countries worked when I finally
went high power with a rebuilt pre-WWII amp running a pair of
TZ-40s. Heady days for a young high school kid!"

Richard Weil, KW0U of St. Paul, Minnesota wrote to tell us about
working DX with a modest station.  He has a half-wave 20 meter
dipole in the attic of his condo, and runs around 100 watts.  He
wrote, "On 31 January at 2310Z I was listening on 14.247 when BX5AA,
Jimmy in Taiwan, came in clear.  We had a solid 2-minute QSO.
Checking later I realized we were right on the greyline--my sunset
time matched his sunrise.  (Years ago I did just the reverse to nail
Marion Island.)  Watching for conditions like this can sometimes be
surprising--and rewarding!"

You can see a photo of Richard and more of his comments at,

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 web page at,  For a detailed
explanation of the numbers used in this bulletin, see  An archive of past
propagation bulletins is at

Monthly propagation charts between four USA regions and twelve
overseas locations are at

Instructions for starting or ending email distribution of this
bulletin are at

Sunspot numbers for February 5 through 11 were 0, 0, 0, 0, 0, 0, and
11 with a mean of 1.6.  10.7 cm flux was 70.1, 70.1, 71.1, 71.2,
70.7, 67.6, and 70.3 with a mean of 70.2.  Estimated planetary A
indices were 7, 2, 3, 4, 4, 3 and 5 with a mean of 4.  Estimated
mid-latitude A indices were 6, 1, 1, 0, 0, 0 and 2 with a mean of