ARRL Propagation Bulletin ARLP015 (2007)

ARLP015 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7RA
Seattle, WA  April 6, 2007
To all radio amateurs 

ARLP015 Propagation de K7RA

Here we are at the bottom of the sunspot cycle, although we won't
know when it occurs for sure until a year after it passes.  This is
because daily and monthly variations are so great that we need to
look at averages derived from many months of daily readings to
determine a cycle peak or minimum.

Because solar activity is so low, comparing this week's average
solar-related indices with last week's doesn't mean much.  Average
daily sunspot number up by half a point, solar flux down 1.1 point,
and the two A indexes we watch rose from 10.4 to 11.7 and 7.7 to 8.

NOAA has yet another revised forecast for the bottom of the cycle,
and it moves the minimum out by one month.  The last projection we
saw in the Weekly Preliminary Report and Forecast had cycle minimum
covering this month and the last two, February through April 2007.
The revised numbers extend it out another month, so the minimum is
spread over February through May 2007.  To see them both, go to and select 1648, the April 3
edition, and look at the table on page 9, then view page 10 in issue

These are predictions for 12-month smoothed numbers, what they would
be if a year of predicted numbers were averaged, and the month in
question in the middle.  So on the most recent table, the latest
month we know the actual smoothed sunspot number is September 2006,
because none of the data which it depends on is predicted.

A different forecast from NOAA puts the minimum for sunspot numbers
at this month.  See it at, and note that
their predicted minimum for solar flux comes four months later.

Two months ago we began tracking our own smoothed sunspot numbers.
Instead of averaging each monthly average (that's right, the 12
month smoothed number is an average of averages) we use a shorter
period, 3 months.  This allows spotting of recent trends.  Now that
March 2007 has passed, we know the 3-month average for February
2007.  Because there were 90 days from January 1 through March 31,
we take the sum of all the daily sunspot numbers for that period
(1,661), and divide by 90.  The result rounds out to 18.5, the
lowest 90-day smoothed number since a year earlier.

Here are the 90-day smoothed sunspot numbers for the past 18 months:

Sep 05 39.3
Oct 05 28
Nov 05 36
Dec 05 40.6
Jan 06 32.4
Feb 06 18.1
Mar 06 27.7
Apr 06 38.5
May 06 39.7
Jun 06 28.9
Jul 06 23.3
Aug 06 23.5
Sep 06 21.2
Oct 06 24.1
Nov 06 23.1 
Dec 06 27.3
Jan 07 22.7
Feb 07 18.5

In the following numbers, note these are averages for each month,
not a smoothed number for 3 months.  Monthly averages of daily
sunspot numbers for February 2006 through March 2007 were 5.3, 21.3,
55.2, 39.6, 24.4, 22.6 , 22.8, 25.2, 14.7, 31.5, 22.2, 28.2, 17.3
and 9.8.  Monthly averages of daily solar flux for the same period
were 76.5, 75.5, 88.9, 80.9, 76.5, 75.8, 79, 77.8, 74.3, 86.3, 84.4,
83.5, 77.7 and 72.2.

From all indications above, this looks like it could be the low
point of cycle 23, although I expect a monthly average sunspot
number closer to zero than ten.  Perhaps we aren't actually there

In the last bulletin, we mentioned N4ZQ, and his vivid memory of
aurora on February 11, 1958, which had a ''night sky as bright as any
noon day'' on Long Island in New York.  Mail came in this week from
others who recall that day.

John Weatherly, AB4ET of Melbourne, Florida writes: ''On that date I
was living in Elizabeth, South Australia and actually on the air as
VK5QL at about 9 PM local time. I had been working Europeans on CW
when in the space of about 3 or 4 minutes 20 meters changed from a
good noise free band full of signals to an S9 hiss with zero
signals. I wasn't sure what happened and started to check my rig's
connections when my XYL, who had been hanging laundry out to dry in
the back yard (mid-summer in VK), came rushing into the shack and
said 'Come quick. Something strange has happened to the sky.' I went
out into the yard to find the entire southern sky covered with the
wavering multicolored glow of the Aurora Australis, stretching up to
and beyond the zenith. As a visitor from the UK (G3KQL), this was
something neither of us had ever seen before (or since). The
phenomena lasted about 45 minutes and then began to fade, the noise
gradually diminished along with it and the signals returned''.

Kerry Webster, WB7AKE of Tacoma, Washington writes about another
experience from 1958: ''My dad worked in a gas station in Centralia,
Washington. One day he was chatting with the local cop, leaning in
the window of the squad car, when the police officer picked up his
microphone to check in with his dispatcher. To his surprise, the
voice that came back was a strange woman with a southern accent,
wanting him to go to 'Peachtree Street.' Turns out the dispatcher
was in Georgia. I remember the cop cars of those days, with their
long whip antennas, so I'm guessing they were on the old 40 MHz low
VHF band.  The incident made a great impression on me, and shortly
afterward I got my first S-38 and started listening for this cool
stuff myself.''

Last weekend I visited Reedley, California, in the San Joaquin
Valley, a little agricultural town where I lived in 1958, when I was
six.  This was my first time back in 47 years, and most of the town
was hard to recognize, having grown five-fold since then.  My father
had a lo-band business radio in the company car in 1958, also
somewhere around 40 MHz, and the outfit he worked for had a similar
situation, with someone in the field depending on an unknown station
in Texas to relay a message to the base station in Fresno.

I was fascinated by this, and a few years later in 1962 would first
hear about amateur radio and see a station up close.  But when I got
my Novice license in 1965, the sunspot activity was way down from
the 1950s, far down.  All I heard from my older ham brethren was
grumbling about the terrible conditions, compared to just a few
years earlier.  Little did we know that over the next five decades
we would experience nothing like 1958-59.

Several more people wrote in this week to talk about the worldwide
communications they still have, even at the bottom of the cycle.
KD0AL in California wrote about the great signal reports he got from
Armenia and Kuwait with his old TA-33jr at 21 feet, and NN0TT in
Minnesota has 289 confirmed with 100 watts CW and one of those
popular commercial verticals with no radials.

Don Prahl, KV7Q of Wilmar, Minnesota writes about the fun we are
having at the bottom of the cycle: ''The amazing reports of activity
in recent months are probably attributable to one key factor --
technology.  I was first licensed in 1962 and, during the minimum of
the mid-60's, remember my frustration at hearing nothing day after
day with my Hallicrafters SX-25.  But hey, this rig was literally in
the stone ages compared to the quality gear we all enjoy today.  I
suspect the same signals we hear today were around then as well - -
they just couldn't be heard.  Add in the fact that there were very
few hams running a full kilowatt, it's no wonder we hated those
sunspot minimums.  Life is good - - technology is great.''

And finally, N6OA wrote to remind us about the interesting
experiment at PropNET,  They are using
automation and PSK31 to operate a real time indicator of current
conditions.  Click on the results on that page, and also find out
how to join the network yourself.

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 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

Sunspot numbers for March 29 through April 4 were 14, 13, 15, 13,
12, 23 and 0 with a mean of 12.9. 10.7 cm flux was 73.8, 74.1, 73.2,
71.7, 71.2, 70.8, and 70.7, with a mean of 72.2. Estimated planetary
A indices were 2, 4, 3, 30, 24, 11 and 8 with a mean of 11.7.
Estimated mid-latitude A indices were 2, 3, 2, 17, 16, 10 and 6,
with a mean of 8.