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SB PROP @ ARL $ARLP048
ARLP048 Propagation de K7RA
ZCZC AP48
QST de W1AW
Propagation Forecast Bulletin 48 ARLP048
>From Tad Cook, K7RA
Seattle, WA November 21, 2008
To all radio amateurs
SB PROP ARL ARLP048
ARLP048 Propagation de K7RA
The latest sunspot appearance lasted eight days, and the spot passed
from view after November 17. Geomagnetic indices have remained nice
and quiet. If you look at
http://www.swpc.noaa.gov/ftpdir/indices/quar_DGD.txt for recent
geomagnetic data, you will notice certain times which were extremely
quiet, with many 0s in the K index. The days since November 16 is
one of those periods. You won't see quiet conditions like this once
we get greater solar activity.
The next time we see unsettled geomagnetic conditions should be
November 25.
Summer is when we see the most sporadic-E skip, but there is another
less pronounced period in the late Fall. Bill Van Alstyne, W5WVO of
Rio Rancho, New Mexico says, "First Es opening of the Winter season
this past week! It was a fairly short opening of moderate strength
between AZ/NM and OR/WA. Hoping for a better Winter Es season this
year than we've had in the past couple, which have been pretty poor
by comparison to earlier years in this decade."
I believe he is talking about E-skip on 6 meters.
Bill also commented on some advantages of higher frequency operation
mentioned in last week's Propagation Forecast Bulletin ARLP047, and
points out the factor of height above ground in wavelengths.
Bill says, "To reduce the effect of phase-canceling ground
reflections and get a low angle of radiation suitable for working
maximum-path-length stations (i.e., long-haul DX), you need to get a
Yagi up around 3 wavelengths above average terrain, at least. Higher
is better. At 20 meters, this is (gasp) about 200 feet! Stacking
Yagis also helps focus the radiated energy at a low angle by nulling
out waves that are radiating at ineffective angles (up and down).
Though there are quite a few Big Guns who have 200-foot towers (and
even higher) with stacked 20-meter Yagis on them, most of us can
only mentally drool about such installations. At 10 meters, though,
3 wavelengths is around 100 feet -- still a pretty tall tower, but a
lot more doable. And, at 6 meters, 3 wavelengths is only around 60
feet!"
He continues, "As you go higher in frequency and shorter in
wavelength, antennas get smaller and more manageable, as you said --
not to mention cheaper! But they also work well closer to the
ground. If you have a triband Yagi at 65 feet, it is going to work
fairly competitively for long-haul DX on 10 meters when that band is
strongly open -- but on 20 meters, the Big Guns with the 200-foot
towers are still going to clean your clock. This is my favorite
reason for liking a higher MUF. And, it is also my favorite reason
for LOVING the 6-meter band. It's a LOT easier to become a Big Gun
on 6 meters than it is on 20 meters! On 6 meters, I run about a kW
(when I need it) into a pair of stacked 5-element Yagis up only
about 40 feet at the top. I'm not saying I'm a Big Battleship Gun
on 6, but I'm definitely a pretty decent Cruiser-size gun, and I can
work a lot of stuff that most other guys in my area can't hear. When
6 is strongly open with double-hop sporadic-E, stations in New
England pile up on me ten deep, and I can run three Qs a minute as
long as the Es holds up. Think I could do that on 20 meters with a
tri-bander at 40 feet? No way!"
Jim Borowski, K9TF of West Allis, Wisconsin wrote asking for info on
any propagation software that runs on the Apple Macintosh. Write to
us and we'll pass on suggestions in the next bulletin.
If you would like to make a comment or have a tip for our readers,
email the author at, k7ra@arrl.net.
For more information concerning radio propagation, see the ARRL
Technical Information Service web page at,
http://www.arrl.org/tis/info/propagation.html. For a detailed
explanation of the numbers used in this bulletin see,
http://www.arrl.org/tis/info/k9la-prop.html. An archive of past
propagation bulletins is at http://www.arrl.org/w1aw/prop/.
Monthly propagation charts between four USA regions and twelve
overseas locations are at http://www.arrl.org/qst/propcharts/.
Instructions for starting or ending email distribution of this
bulletin are at http://www.arrl.org/w1aw.html#email.
Sunspot numbers for November 13 through 19 were 16, 12, 11, 11, 11,
0, and 0 with a mean of 8.7. 10.7 cm flux was 69.1, 68.3, 68.2,
67.7, 67.7, 69.8, and 69.4 with a mean of 68.6. Estimated planetary
A indices were 1, 1, 6, 8, 2, 1 and 1 with a mean of 2.9. Estimated
mid-latitude A indices were 2, 1, 3, 7, 2, 0 and 1 with a mean of
2.3.
NNNN
/EX
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