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ARRL Propagation Bulletin ARLP043 (2010)

ARLP043 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 43  ARLP043
From Tad Cook, K7RA
Seattle, WA  October 29, 2010
To all radio amateurs 

ARLP043 Propagation de K7RA

The daily sunspot number went all the way to 74 this week (on
Tuesday, October 26), but the average sunspot number was down over
five points from the previous week, to 50.3.

Several sunspot groups contributed this week.  1113 first appeared
October 13, and was visible through October 26.  1115 emerged on
October 15, and ran through October 27, its last day.  1117 emerged
October 19, and was still growing yesterday, October 28.  But 1117
is now approaching the western horizon, and is less and less

The latest prediction is for solar flux of 85 through October 31, 82
on November 1 and 78 on November 2-5, then 80 on November 6-11, and
rising after that.  Predicted planetary A index for October 29
through November 1 is 5, 8, 5 and 7, then back to 5 on November
2-17.  Geophysical Institute Prague sees quiet to unsettled
conditions October 29-30, quiet October 31 through November 1,
November 2-3 unsettled, and November 4 quiet to unsettled.

Conditions shouldn't be bad this weekend for the CQ World Wide SSB
DX Contest.  Geomagnetic conditions should be relatively quiet, and
we've had a little sunspot activity of late.  But with sunspot group
1117 disappearing, unless a new one emerges, the sunspot number
could drop back to zero.

A look at the STEREO mission at shows
some possible activity just over the eastern horizon.  There is also
a very bright area, indicating magnetic activity straddling the
unseen sector, which keeps getting smaller. Coverage should reach
96% around 1014 UTC on November 1, 97% at 0014 UTC on November 22,
98% coverage at 0014 UTC on December 14, and 99% at 1700 UTC on
January 7, 2011.

Check for a dramatic Sun photo taken on
October 20 by amateur astronomer Alan Friedman with a small
telescope.  Thanks to "Phil Plait's Bad Astronomy Blog" at for this.

Rich Dowty, W7EET reminds us of the DX Sherlock maps for propagation
on 28 MHz and higher.  See and
dial in your favorite band and region.

Stu Phillips, K6TU had some comments regarding remarks I had in last
week's Propagation Forecast Bulletin ARLP042 regarding WSPR real
time data and how it might be used for evaluating propagation paths
for other modes, such as SSB and CW.

He writes, "For every WSPR spot (which you can see in the database
at the website), there is a power level in dBm and a
signal to noise ratio reported by the receiving station.

"Although the antenna used by the transmitting station isn't known,
you can get a pretty good idea of the path and what it would take in
terms of increased ERP to successfully conclude either a CW or a SSB
contact.  I've also found pretty good correlation between
propagation predictions using VOACAP that when adjusted for
bandwidth (WSPR calculates SNR assuming a 2.5 kHz effective
bandwidth) and power levels, correspond pretty closely with the SNR
levels reported by WSPR.

"So pick you reference point - for example, if you need 12 dB SNR in
a 200 Hz bandwidth to complete a CW contact, you can scale the WSPR
report by adding 10 dB for the bandwidth delta and then scale
appropriately for power/ERP delta.  Most WSPR transmissions on the
HF bands are 5 watts or less - so even a "standard" ham transmitter
at the 100 watt level is a further uplift of 13 dB even without ERP
boost from a decent antenna."

We'll have more information next week from K6TU regarding WSPR and

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 October 21 through 27 were 34, 34, 43, 57, 57,
74, and 53, with a mean of 50.3. 10.7 cm flux was 83.5, 82.2, 84.3,
82.1, 86.2, 86.1 and 87.6 with a mean of 84.6. Estimated planetary A
indices were 3, 6, 23, 14, 6, 8 and 4 with a mean of 9.1. Estimated
mid-latitude A indices were 1, 4, 16, 10, 4, 6 and 3 with a mean of


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