The K7RA Solar Update
Sunspots returned this week, or rather, one did, but it is an old Solar Cycle 23 spot. Sunspot 1012 has been visible the last couple of days, February 11-12. It is down near the Sun's equator, typical for spots from a previous cycle. It's nice to have a sunspot, but it doesn't indicate activity from the new Solar Cycle 24, which has been so eerily quiet. Sunspot numbers for February 5-11 were 0, 0, 0, 0, 0, 0 and 11 with a mean of 1.6. The 10.7 cm flux was 70.1, 70.1, 71.1, 71.2, 70.7, 67.6 and 70.3 with a mean of 70.2. The estimated planetary A indices were 7, 2, 3, 4, 4, 3 and 5 with a mean of 4. The estimated mid-latitude A indices were 6, 1, 1, 0, 0, 0 and 2 with a mean of 1.4.
We saw a few days this week when the geomagnetic activity was very, very low. Look here and note all the zeroes from February 8-10 in both the middle latitude and high latitude numbers. We could see some geomagnetic activity this weekend due to energy from a solar wind stream. The predicted planetary A index from NOAA for February 13-19 is 5, 10, 15, 10, 5, 5 and 5. Geophysical Institute Prague sees slightly earlier activity, with quiet on February 13, unsettled February 14, quiet to unsettled February 15 and quiet February 16-19.
If we get at least a few days that have a sunspot number of 11 (the minimum non-zero sunspot number), it makes a difference in the MUF of many paths. For instance, with no sunspots, the projected path from Philadelphia to France for today shows MUF values every half hour from 1500-1900 UTC as 17.7, 18.2, 18.5, 18.6, 18.5, 18.4, 17.4, 16.5 and 15.4 MHz. With a sunspot number of 11 for several days, the MUF values change to 19.4, 20, 20.1, 20.1, 20, 19.5, 18.3, 17.3 and 16.2 MHz.
Over the same path (with no sunspots over the same time period), the odds of communication on 17 meters would be 25-50 percent at 1500 UTC, 50-75 percent at 1530-1730 UTC, 25-50 percent at 1800 UTC and less than 25 percent at 1830-1900 UTC. With a sunspot number of 11 for several days, the same Philadelphia to France path would have odds of success on 17 meters of 75-100 percent from 1500-1700 UTC, 50-75 percent at 1730-1800 UTC, 25-50 percent at 1830 UTC, and less than 25 percent at 1900 UTC.
Last week's Solar Update contained a comment about 10 meter propagation, and that Great Britain used a system operating from 30-50 MHz in the World War II era for over-the-horizon radar, known as Chain Home. This brought an interesting e-mail from Brett Graham, VR2BG, about Chain Home, and later HF OTH radar systems. Brett says Chain Home operated on 20-30 MHz. For images of Chain Home antenna towers, look at here, here and here. You can watch an online video of Brett explaining the history of OTH radar and modern uses at a multimedia messaging server, mms://max-server.net/2008_vr2bg. Just click on that link, or paste it into your Web browser's URL field without the usual http:// at the front. This was recorded at the 2008 Asia-Pacific DX Convention in November in Osaka, Japan.
Many of us recall the Russian Woodpecker OTH system of past years and the huge amount of QRM it generated all over the HF spectrum. Check out some photos of those systems here, here and here. I believe at least one of those images is from inside the Chernobyl exclusion zone. Brett comments on the video that it took a lot of electrical power to drive those huge arrays. On the video, Brett gives a great deal of information concerning current HF OTH systems operated by different countries and the type of threat they present to HF communications.
Joe Schroeder, W9JUV, of Glenview, Illinois, sent this memory of Chain Home signals after World War II: "N6TP's comment on Chain Home radar really brought back memories! I was a newly minted ham in 1946 and when 10 meters (the only HF band the military had released for ham use!) opened to Europe in the fall, we used the Chain Home buzz on the high end of the band to judge band conditions to Europe. I was using a homemade 2-element Yagi roped to the top of the chimney and 50 W to an 807. When the FCC gave us the 27 Mc band, we'd sometimes work Europe duplex by calling CQ continuously on 11 meters and announcing 'Tuning 28.3 to 28.4 for any calls.' My 807 and I had 52 countries worked when I finally went high power with a rebuilt pre-WWII amp running a pair of TZ-40s. Heady days for a young high school kid!"
Richard Weil, KW0U, of St Paul, Minnesota, wrote to tell us about working DX with a modest station. He has a half-wave 20 meter dipole in the attic of his condo and runs around 100 W. He wrote, "On January 31 at 2310 UTC, I was listening on 14.247 when BX5AA, Jimmy in Taiwan, came in clear. We had a solid two minute QSO. Checking later, I realized we were right on the grey line -- my sunset time matched his sunrise (years ago, I did just the reverse to nail Marion Island). Watching for conditions like this can sometimes be surprising -- and rewarding!" You can see a photo of Richard and more of his comments at here.
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.