The average daily sunspot numbers declined 38 points to 106.7 this week, while the average daily solar flux declined nearly 18 points to 116.2. Sunspot numbers for April 26-May 2 were 117, 99, 118, 114, 104, 99 and 96, with a mean of 106.7. The 10.7 cm flux was 119.2, 117.9, 121.1, 116, 114.1, 109.9 and 115.5, with a mean of 116.2. The estimated planetary A indices were 17, 8, 5, 5, 3, 4 and 5, with a mean of 6.7. The estimated mid-latitude A indices were 17, 7, 5, 5, 2, 3 and 4, with a mean of 6.1

The predicted solar flux is 115 for May 4-6, 110 on May 7-10, 120 on May 11, 130 on May 12, 135 on May 13, 140 on May 14-17, 135 on May 18-21, going down to 130, 125, 120, 115 and 110 on May 22-26, and finally 105 on May 27-31. The predicted planetary A index is 5 on May 4-8, then 10, 10 and 8 on May 9-11, 5 on May 12-13, 8 on May 14-15, then 5, 8, 5, 8 and 10 on May 16-20, 15 on May 21-23, 8 on May 24, 5 on May 25-June 4, followed by 15 on June 5-6.

The NASA solar cycle prediction from the Marshall Space Flight Center changed over the past month. The predicted maximum smoothed international sunspot number declined slightly from 61 to 60, but it still is predicted for spring 2013. The date of the new prediction is May 1, 2012 and last month’s was on April 2, 2012. International sunspot numbers have much lower values than the sunspot numbers we use in this bulletin.

Sunspot numbers have generally declined from a peak during the fall of 2011. We look at a three month moving average every month, and now that we know the numbers for all of February through April, we know the average sunspot number centered on March, which was 71.2. The three month moving sunspot number averages centered on January, 2011-March 2012 are 35.3, 55.7, 72.3, 74.4, 65.9, 61.5, 63, 79.6, 98.6, 118.8, 118.6, 110, 83.3, 73.7 and 71.2. The three month moving average smoothes out the numbers so we can see a steady downward trend since October and November 2011, when the numbers were 118.8 and 118.6. But looking at the monthly averages, we can see a recent uptick. The monthly average sunspot numbers for October 2011-April 2012 are 123.6, 133.1, 106.4, 91.4, 50.1, 78 and 84.5. Note that the average sunspot number for the past week -- 106.7 -- is higher than any monthly average since December 2011.

There is an interesting article out of Cornell University, “The Science Behind Solar Storms.”

Bruce Clark, K0YW, of Ignacio, Colorado, offered the following comments about noise figure and preamplifiers: “At 6 meters and below, the employment of a pre-amp ahead of most modern transceivers is not likely to result in any noticeable improvement, as the ambient thermal noise from the Earth and sky background is high enough to readily overcome the sensitivity threshold of the existing receiver’s RF stage/s, especially if the myriads of local manmade noise sources are added in. It is this combination of factors that will establish the ‘noise floor’ that the radio sees. Even if the receiver’s sensitivity is improved by lowering its noise figure -- either at the receiver or with an external antenna mounted pre-amp -- it will not generally improve performance vs weak signals at or under the existing noise floor. Such pre-amps do a good job of making that noise louder along with the weak signal, resulting in no real signal-to-noise improvement. Depending on its gain, it can also seriously degrade the receiver’s dynamic range, increasing the likelihood of overload or cross modulation interference from strong, close-by stations that are off frequency.

“Pre-amps become effective if receive feedline loss is excessive, or if the receiver noise figure is poor. This condition is very rare at HF and 6 meters. It usually becomes a factor at frequencies in the UHF region and higher, especially where extreme feedline lengths or lossy coaxial feedlines are used. Every dB of feedline loss will be seen as an extra dB increase in the receiver’s noise figure. While this is a serious consideration at 432 and 1296 MHz and higher, it is of little concern at HF and 6 meters where pre-amplifier-equipped transceivers achieve noise figures in the 4-8 dB region. At 6 meters, these noise figures are very adequate to hear the weakest signals. Good feedline -- like LMR series, waterproof versions of 9913 or 1/2 Inch Heliax on short runs of less than 150 feet -- are a lot cheaper way to optimize performance on 6 meters than an expensive antenna mounted pre-amp.”

Rich Zwirko, K1HTV, sent in the following propagation report: “The HF bands were in pretty good shape when the 7O6T DXpedition to Yemen showed up on April 30 at 2104 with an S9+ signal on 15 meters. I was 7O6T’s second 15 meter CW QSO, easily working them simplex with my barefoot transceiver and 3-element tribander. They quickly went split and as soon as a DX Cluster post was made, the expected huge pileup began! In the next few days, I managed to work 7O6T on both CW and SSB on 20, 17 and 15 meters. We had an interesting late afternoon East Coast opening to the Yemen DXpedition on May 2. I contacted 7O6T at 2124 (0024 local Yemen Time) on 12 meter SSB, again with 100 W, using a wire antenna. Six meter E-s openings on the afternoon of May 2 provided FL31 and FL32 water grids to a number of stations up and down the East Coast. I worked UT1FG, who was operating maritime mobile southeast of the Bahamas, on 50.110 MHz. Yuri is captain of the cargo ship Mottler. With his 100 W and dipole, he has been having fun with E-skip, providing a number of new grids to ops on the Magic Band.”

All times listed are UTC, unless otherwise noted.

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 each Thursday in The ARRL Letter. You can find a guide to articles and programs concerning propagation here. Check here and 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.