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The K7RA Solar Update

11/21/2008

The latest sunspot appearance lasted eight days; the spot passed from view after Monday, November 17. Geomagnetic indices have remained nice and quiet. If you look here for recent geomagnetic data, you will notice certain times which were extremely quiet with many zeroes in the K index. One of those periods is the days after November 16. 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.

Sunspot numbers for November 13-19 were 16, 12, 11, 11, 11, 0 and 0 with a mean of 8.7. The 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. The estimated planetary A indices were 1, 1, 6, 8, 2, 1 and 1 with a mean of 2.9. The estimated mid-latitude A indices were 2, 1, 3, 7, 2, 0 and 1 with a mean of 2.3.

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, "The first Es opening of the winter season was 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 six meters.

Bill also commented on some advantages of higher frequency operation mentioned in the last week's bulletin and points out the factor of height above ground in wavelengths: "To reduce the effect of phase-canceling ground reflections and get a low angle of radiation suitable for working maximum-path-length stations (such as 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 tall 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!

"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 tri-band 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, those with the 200 foot tall 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 kilowatt (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-sized 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 10 deep and I can run three QSOs 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, Jose!"

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.

Amateur solar observer Tad Cook, K7RA, of Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version appears in The ARRL Letter. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.



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