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ARRL Propagation Bulletin ARLP018 (2012)

ARLP018 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 18  ARLP018
From Tad Cook, K7RA
Seattle, WA  May 4, 2012
To all radio amateurs 

ARLP018 Propagation de K7RA

Average daily sunspot numbers declined 38 points to 106.7 this week,
and average daily solar flux declined nearly 18 points to 116.2.

Predicted solar flux is 115 for May 4-6, 110 on May 7-10, 120 on May
11, 130 on May 12, 135 on May 13, 140 on May 14-17, 135 on May
18-21, and 130, 125, 120, 115, 110 on May 22-26 and 105 on May

Predicted planetary A index is 5 on May 4-8, then 10, 10 and 8 on
May 9-11, 5 on May 12-13, 8 on May 14-15, then 5, 8, 5, 8, and 10 on
May 16-20, 15 on May 21-23, 8 on May 24, 5 on May 25 through June 4,
followed by 15 on June 5-6.

The NASA solar cycle prediction from the Marshall Space Flight
Center at changed
over the past month.  The predicted maximum smoothed international
sunspot number declined slightly from 61 to 60, but still is
predicted for Spring 2013. The date of the new prediction is May 1,
2012 and last month's was on April 2, 2012. International sunspot
numbers have much lower values than the sunspot numbers we use in
this bulletin.

Sunspot numbers have generally declined from a peak during Fall
2011.  We look at a 3-month moving average every month, and now that
we know the numbers for all of February through April, we know the
average sunspot number centered on March, which is 71.2. The 3-month
moving sunspot number averages centered on January, 2011 through
March 2012 are 35.3, 55.7, 72.3, 74.4, 65.9, 61.5, 63, 79.6, 98.6,
118.8, 118.6, 110, 83.3, 73.7 and 71.2. The three month moving
average smooths out the numbers so we can see a steady downward
trend since October and November 2011, when the numbers were 118.8
and 118.6.

But looking at the monthly averages, we can see a recent uptick. The
monthly average sunspot numbers for October 2011 through April 2012
are 123.6, 133.1, 106.4, 91.4, 50.1, 78 and 84.5.  Note that the
average sunspot number for the past week - 106.7 - is higher than
any monthly average since December 2011.

Interesting article out of Cornell University, "The Science Behind
Solar Storms." Read it at,

Jim Spears, N1NK of Tiverton, Rhode Island, Roger Larson, KF6IVA of
Harrison, Maine, Paul Dluehosh, N4PD of Leesburg, Virginia, Bruce
Clark, K0YW of Ignacio, Colorado and Jon Jones, N0JK of Lawrence,
Kansas all pointed out that the abbreviation NF that was referenced
in the last bulletin, Propagation Forecast Bulletin ARLP017, refers
to Noise Figure, not Noise Floor.

N0JK sent this link:

K0YW offered the following comments about noise figure and

"At 6 Meters and below the employment of a preamp ahead of most
modern transceivers is not likely to result in any noticeable
improvement, as the ambient thermal noise from the earth and sky
background is high enough to readily overcome the sensitivity
threshold of the existing receiver's RF stage/s, especially if the
myriads of local man made noise sources are added in. It is this
combination of factors that will establish the 'Noise Floor' that
the radio sees. Even if the receiver's sensitivity is improved by
lowering its noise figure - either at the receiver or with an
external antenna mounted preamp - it will not generally improve
performance vs. weak signals at or under the existing noise floor.
Such preamps do a good job of making that noise louder along with
the weak signal, resulting in no real S/N improvement. Depending on
its gain it can also seriously degrade the receiver's dynamic range,
increasing the likelihood of overload or cross modulation
interference from strong, close-by stations that are off frequency.

"Preamps become effective if receive feedline loss is excessive, or
if the receiver noise figure is poor. This condition is very rare at
HF and 6 meters. It usually becomes a factor at frequencies in the
UHF region and higher, especially where extreme feedline lengths or
lossy coaxial feedlines are used. Every dB of feedline loss will be
seen as an extra dB increase in the receiver's noise figure. While
this is a serious consideration at 432, 1296 and higher, it is of
little concern at HF and 6 Meters where preamplifier equipped
transceivers achieve noise figures in the 4-8 dB region. At 6
meters, these noise figures are very adequate to hear the weakest
signals.  Good feedline, like LMR series, waterproof versions of
9913 or 1/2 inch Heliax on short runs of less than 150 ft are a lot
cheaper way to optimize performance on 6M than an expensive antenna
mounted preamp."

Rich Zwirko, K1HTV sent in the following propagation report:

"The HF bands were in pretty good shape when the 7O6T DXpedition to
Yemen showed up on April 30 at 2104Z with an S9+ signal on 15
meters. I was 7O6T's second 15 meter CW QSO, easily working them
simplex with my barefoot K3 and 3 element tribander. They quickly
went split and as soon as a DX Cluster post was made, the expected
huge pileup began. In the next few days I managed to work 7O6T on
both CW and SSB on 20, 17 and 15 meters. We had an interesting late
afternoon East Coast opening to the Yemen DXpedition on May 2. I
contacted 7O6T at 2124z (that's 0024 local Yemen Time) on 12 meter
SSB, again with 100 Watts, using a wire antenna.

"Six meter Es openings on the afternoon of May 2 provided FL31 and
FL32 water grids to a number of stations up and down the East coast.
I worked UT1FG/MM, operating maritime mobile southeast of the
Bahamas, on 50.110 MHz. Yuri is captain of the cargo ship Mottler.
With his 100 Watts and dipole he has been having fun with E-skip,
providing a number of new grids to ops on the Magic Band."

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 an explanation of the
numbers used in this bulletin, see An archive of past
propagation bulletins is at Find more good
information and tutorials on propagation at

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

Instructions for starting or ending email distribution of ARRL
bulletins are at

Sunspot numbers for April 26 through May 2 were 117, 99, 118, 114,
104, 99, and 96, with a mean of 106.7. 10.7 cm flux was 119.2,
117.9, 121.1, 116, 114.1, 109.9 and 115.5, with a mean of 116.2.
Estimated planetary A indices were 17, 8, 5, 5, 3, 4, and 5, with a
mean of 6.7. Estimated mid-latitude A indices were 17, 7, 5, 5, 2,
3, and 4, with a mean of 6.1.


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