ARRL Propagation Bulletin ARLP020 (2010)

ARLP020 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 20  ARLP020
From Tad Cook, K7RA
Seattle, WA  May 21, 2010
To all radio amateurs 

ARLP020 Propagation de K7RA

Eleven days with no sunspots, but something emerged late Thursday,
and it may be the return of old sunspot group 1069.  Sunspot group
1069 was visible from May 4-8 before disappearing over the horizon.
The return of that sunspot gives a daily sunspot number of 12 for
May 20.

Average daily solar flux for this reporting week (Thursday through
Wednesday, May 19) was down 6.6 points to 69.2.  Solar flux for
Tuesday through Thursday, May 20 was 68.7, 68.6 and 68.8.  Predicted
solar flux for May 21-27 is 70, 72, 72, 74, 74, 74, and 76, and May
28 through June 4 is 80.

Geophysical Institute Prague predicts unsettled conditions for May
21, quiet to unsettled May 22, and quiet May 23-27.  Predicted
planetary A index from NOAA and USAF is 8 and 6 for May 21-22, 5 for
May 23-28, then 25, 20 and 10 for May 29-31.

Clif Inabinet, KF4UOR of St. Matthews, South Caroline testifies that
he can still have fun on HF with no sunspots.  On May 20, 2010 at
0304z he worked KH6QR, a 4,647 mile path, on 20 meter SSB.  He was
running 160 watts into a 130 foot Windom wire antenna at 39 feet,
and at the other end was 500 watts and a 6 element triband Yagi.
You can actually see the KH6QR antenna at
if you click on Aerial, select "Bird's Eye," and zoom in.  He is on
the west side of Himeni Place.

This is not unusual propagation though, and is an expected path for
this time, frequency and date.  If you download W6ELprop at and enter 33.66 North Latitude and
80.77 West Longitude for Clif's end of the circuit, and 19.67 North
Latitude and 155.98 West Longitude for the Hawaii end, then use the
date of May 20, and enter a solar flux value of 69, you can see that
20 meter signals should begin to get strong around 0100z and
increase in signal strength until 0500z, and the path should remain
open at that signal level at least through 0530z.  You can also see
from W6ELprop how we calculated the length of the path.

This prediction also shows a good path on 40 meters from 0430-1130z,
and 30 meters from 0330-1130z.

Sometimes we get requests such as, "Why not just publish on the web
a green light telling me when conditions are good, and a red light
when conditions are bad?"  The problem is, which of the millions of
possible paths between all different locations would the light
symbolize, and for what frequency and time of day?

Using W6ELprop and an average of several day's solar flux or sunspot
numbers from you can
calculate the likelihood of propagation between your location and
anywhere else for 80-10 meters during any time of the day.  This is
also useful for looking at the effects of seasonal variations on any

Jon Jones, N0JK in Wichita, Kansas reported working OA4TT (Peru) on
6 meters on May 10 using a loop antenna in his attic.  He sent a
long list of DX stations who worked stations mostly in the South and
Midwest from 2320-2348z that day.

Check for a nice description of the
station at OA4TT, who is also N6XQ.

Other DX stations on N0JK's list were TI2NA (Costa Rica), 9Y4D,
9Y4VU and 9Z4BM (Trinidad and Tobago), TG9AWS and TG9NX (Guatemala),
YN2N (Nicaragua see for photos), XE1FAS
and XE2OR.

Concerning the same opening, Bob Miles, K9IL of Martin, Tennessee
(EM56) reported "On May 10 we had a good opening to Central and
South America. OA4TT was workable for 2.5 hours Monday afternoon. I
worked HP3TA Louis also. After I worked Jack OA4TT my XYL W9DHD
walked into the shack. I asked her if she wanted to work him. She
got him in one call. We run 100 watts to 5 elements at 55 feet."

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email the author at,

For more information concerning radio propagation, see the ARRL
Technical Information Service web page at, For an 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

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Sunspot numbers for May 13 through 19 were 0, 0, 0, 0, 0, 0, and 0
with a mean of 0. 10.7 cm flux was 69.4, 69.7, 70.3, 68.5, 69.2,
68.7 and 68.6 with a mean of 69.2. Estimated planetary A indices
were 4, 3, 4, 4, 6, 6 and 8 with a mean of 5. Estimated mid-latitude
A indices were 2, 1, 2, 3, 4, 4 and 7 with a mean of 3.3.