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ARRL Propagation Bulletin ARLP034 (2008)

ARLP034 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 34  ARLP034
From Tad Cook, K7RA
Seattle, WA  August 15, 2008
To all radio amateurs 

ARLP034 Propagation de K7RA

Thanks to Carl Luetzelschwab, K9LA for writing the excellent
bulletin last week.  If you missed it, be sure to check because it is full
of useful information.

Our sun is still not producing any sunspots.  As mentioned in
previous bulletins, the peak of the last cycle was a double peak, so
perhaps we are in the midst of an extended bottom.

Roger Lapthorn, G3XBM reported six-meter observations.

''Following on from comments in the Aug 8th propagation bulletin, I'd
like to mention Aug 6th when, here in the UK on just a small VHF
collinear, I heard both D4C and K1TOL on 6m CW. The Cape Verde
station was working a string of EU stations and peaked at 539 with
me. Lefty, K1TOL (who I worked last year on 6m with just 2.5W!) was
569 and a solid signal for 15 minutes. A little later I was able to
work N2MM on 10m SSB with just 10W and a halo antenna.

My summary is that 6m (and 10m) truly is a magic band if one can
hear such DX on such a simple antenna ...and at sunspot minimum.
Last year's experience of working K1TOL confirmed that it is
possible to work such DX too with a bit of luck and decent

The following is from Scott Bidstrup, WA7UZO, and is so interesting
I thought I should include it in its entirety.

''I live in Costa Rica (EK70rc), and at this low latitude,
propagation is significantly different than in the States.  I have
been having a lot of fun exploring those differences, and recently
downloaded and installed BeaconSee to watch propagation from the
NCDXF/IARU beacon network.  And I have noticed something you might
find to be quite interesting.

While monitoring the NOAA space weather page at I discovered that when a
boundary crossing occurs, there seems to be a mode switch in the
propagation I see here in Costa Rica.

If the Bz component is strongly positive, on 20m. and 15m., I see
fairly strong signals from the 4U1UN beacon in New York, and
moderately strong signals from the OA4B beacon in Peru. I can also
see a weak signal from W6WX and occasionally KH6WO, and in the early
morning from the ZS6 and 5Z4 beacons as well. When a boundary
crossing occurs, it's like someone throws a switch - over three or
four minutes, 4U1UN fades, the W6 and KH6 beacons disappear, and
OA4B booms in.  The bands will get somewhat noisy until the Bz
becomes settled in the decidedly negative, at which point the noise
will subside and the OA4B beacon will become so strong I can even
hear it in the 100mw mode. But I can hear practically nothing else
on the band, and see the 4U1UN beacon only very weakly.  When the
bands are in this mode, 10m. is open to South America, but only to
stations in an arc across the middle of the continent from Santiago
to a range from Buenos Aires to Sao Paulo - no other stations need

This bimodality seems to be inversely correlated to solar wind
speed. the higher the wind speed, the smaller the effect.  It seems
to be positively correlated with the proton density - the stronger
the proton flux, the stronger the signals from South America''.

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

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

Sunspot numbers for August 7 through 13 were 0, 0, 0, 0, 0, 0, and 0
with a mean of 0.  10.7 cm flux was 66.1, 65.5, 65.5, 65.6, 65.7,
65.2, and 65.3 with a mean of 65.6.  Estimated planetary A indices
were 4, 4, 18, 13, 7, 6 and 5 with a mean of 8.1.  Estimated
mid-latitude A indices were 3, 3, 16, 9, 6, 6 and 3 with a mean of


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