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 Previous: The Novice License Helped Shape the '50s Ham Generation |  Next: Surfin': Covering Amateur Radio |
SEATTLE, WA, Jul 28, 2006--There wasn't much change from last week to this week, with average daily sunspot numbers down by less than five points to 14.6. This doesn't result in high enough MUF (maximum usable frequency) values to see much propagation on the highest HF bands, such as 10, 12 and 15 meters. But even with a low MUF, there is still occasional long-distance propagation on 10 and 6 meters.
Larry Godek, W0OGH, of Gilbert, Arizona, reports he monitors 6 and 10 meter FM all day. Larry scans many channels on both bands with multiple receivers. On 29.62 MHz, he's heard W1OJ in Boston and another repeater in Florida, although not so much recently. Lately he hears quite a bit of W5DFW in Dallas on 29.66 MHz. On Tuesday, July 25, Larry was hearing W5DFW alternating with a California station. On the same day he heard a repeater on 53.09 MHz, but didn't catch the ID. He suspects it was in Oklahoma or Texas. He also heard stations near Sacramento, California.
For parsing those mystery signals, Larry wishes he had a database of 6 and 10-meter FM repeaters that he could sort by frequency. Ideally, it would cover all of North America, so he wouldn't need to look through separate state lists.
Joe Alvin, KB1JVW, of White River, Vermont, wants to know how current sunspot numbers affect MUF. Generally speaking, the MUF is lower with lower sunspot numbers, but there is quite a bit of variation depending on where the two ends of the communication path are located. For instance, from Joe's location, the MUF recently (calculating from average sunspot numbers using a propagation prediction program) on a path to Germany would vary from 13.3 MHz at 0300 UTC to a peak above 17 MHz from 1500-1530 UTC and 1830-2030 UTC, and up to 17.4 MHz around 0000 UTC. But with the same sunspot number on the same date, the path from Dallas to Costa Rica would show an MUF that peaks above 24 MHz from 2330-0230 UTC and dips below the 20-meter band around 0900-0930 UTC.
A few years from now, if the sunspot number rises to around 100, that path from Dallas to Costa Rica would peak above 28 MHz from 1730-2200 UTC and around 0200 UTC.
Over the next week, don't expect any huge increase in sunspot numbers. We are near the bottom of the solar cycle and in the summer season, which is not as interesting as fall or spring for working long distances. But if the predictions are correct, a little more than a year from now the sunspot count should be heading higher than it is now, and the MUF will rise with it.
Dean Wilmoth, KC0SRM, of Sturgeon, Missouri, asks about trends over the next weeks and months. Sunspot numbers will still be low, and will head lower, but of course seasonal effects will change. For a path from his area to Central America, for instance, 20 meters will prove more reliable than 17 meters or higher. But move that out two months, and 20 meters will be closing earlier, and 17 meters will be more useful during the day than it is now. Also, with longer nights and less seasonal noise from thunderstorms both near and far, 80 and 40 meters will improve in the fall compared to summer.
Currently, early Friday, July 28, there is a strong solar wind stream hitting Earth, and the planetary K index is at 6. This should decline over the next couple of days, but then come back again on Tuesday. Lower geomagnetic indices generally mean better HF propagation, or at least not as poor as it is commonly when the K index is high. The predicted planetary A index for Friday through Tuesday, July 28 to August 1 is 15, 5, 5, 12 and 20.
For More Information
For more information concerning propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service Propagation page and the article "The Sun, the Earth, the Ionosphere: What the Numbers Mean, and Propagation Predictions," by Carl Luetzelschwab, K9LA. An archive of past bulletins is on the ARRL Web site.
Weekly Sunspot Numbers
Sunspot numbers for July 20 through 26 were 14, 12, 0, 21, 19, 16 and 20, with a mean of 14.6. 10.7 cm flux was 72.2, 72.6, 73.6, 76.5, 77, 75.5, and 74.7, with a mean of 74.6. Estimated planetary A indices were 3, 2, 4, 4, 4, 6 and 6, with a mean of 4.1. Estimated mid-latitude A indices were 2, 1, 3, 4, 7, 5 and 5, with a mean of 3.9.
Amateur solar observer Tad Cook, K7RA, 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. Readers may contact
the author via e-mail.
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