Tuesday, November 27, 2007
ARLP049 Propagation de K7RA
This is an off-schedule post-Thanksgiving bulletin. Because ARRL headquarters was closed on Friday, the day this bulletin is normally released, and the last Propagation Forecast Bulletin ARLP048 was written before the end of our reporting week (which is Thursday through Wednesday), the sunspot, solar flux and geophysical numbers normally at the end of the bulletin are in this bulletin, but were not a part of ARLP048. Friday, November 30 will find us back on the regular schedule with Propagation Forecast Bulletin ARLP050.
The last propagation bulletin reported a brief return of sunspots on November 16-17, when sunspot group 974 emerged, and the sunspot number was 13 on both days. There were six more days of no spots, then November 24 saw the emergence of group 975, with a sunspot number of 15. The next day the sunspot number declined to 12, and the area it covered was about half the area on the previous day.
A solar wind stream on November 20 caused the most active recent geomagnetic day, with the planetary A index rising to 28, and Alaska's high-latitude college A index going to 48. Geomagnetic indices were somewhat unsettled over the last weekend (November 24-25), but are quieting down now, with the expected planetary A index at 10 for today, November 26, and then 5 until December 11. The planetary A index over November 22-25 was 13, 10, 12, and 11. The numbers for the seven days previous to that are listed below.
Unexpected bottom-of-the-cycle propagation still crops up. On November 21, a number of Northeast United States stations reported working Central and South America on 10 meters. W1RM worked Mozambique on 12 meters and Ecuador on 10 meters.
In Propagation Forecast Bulletin ARLP047 on November 16 we mentioned briefly some unusual daylight DX on 75 meters. Note that most of these stations had what many of us would consider monster directional antenna arrays for 75 meters, such as 2-3 element Yagis anywhere from 100-165 feet.
Glenn Rattmann, K6NA of Valley Center, California wrote, "I have been a serious DXer on 75/80m for more than 35 years, and we observed something there on November 10 that hasn't been seen much before, at least among the west coast 75m morning longpath DX crowd. A number of folks here worked a group of ZS stations on 3795 kHz under unusual circumstances."
He continues, "As you know, working into the Middle East, Diego Garcia, and Europe on 75m longpath from the west coast is a fairly routine occurrence during the period November through February. Northeast Africa would also be commonly worked on this grayline path, but for the lack of activity in places like SU, J28, ET3."
He goes on to say, "However, historically there has not been propagation to the southern part of Africa during the west coast sunrise-grayline window, because the position of the grayline is not favorable. Although we in the northern hemisphere are moving into shorter and shorter days (later sunrise too), in the southern latitudes they are moving into more and more daylight. It is possible that a far northwestern station in Seattle, or VE7 land, with the latest sunrise time, has worked a 5R8. Speaking personally, I have never heard of someone working a ZS--even further west than 5R8--on this path. The other significant item is that normally the most easterly and southerly stations in California (that would be San Diego, where I am) have the earliest sunrise, and therefore tend to lose the band earlier than others north and west of us. Typically one hears long path signals fading completely by about 25 minutes after local sunrise on our end."
Glenn continues, "The short story regarding why we don't hear ZS stations on the longpath on 75m is: Sunrise occurs on the west coast 'too soon,' in conjunction with the sunset period occurring 'too late' in South Africa (southern latitudes), even for stations in WA or BC. However, on November 10th such an opening did occur to ZS."
He goes on to say, "I came to the band a bit late that morning, and immediately heard K7ZV and W6KW working a ZS. I listened a while, and they worked several ZS stations in a roundtable. I called in at 1555Z--already one hour and forty minutes after my sunrise!--and logged ZS4TX who gave me a 59 plus report. He was true S-7 on my S-meter. The other California stations received similar reports for the most part. I copied perfectly several other ZS stations but didn't bother to work them; some were using low power and low dipole antennas. All said they had never worked a US west coast station prior to this. I heard ZS4TX say that his sunset would be 'after 1700Z sometime.' So all stations on both ends of the path were in full daylight with significant overlap, although of course much of the path had to be in darkness or something approaching grayline."
He continues, "Note, there were no "regular" longpath signals, i.e. those from Zone 15-16-20-21, audible at all during this opening."
Glenn continues with, "A brief timeline: San Diego sunrise Nov. 10th: 1414Z. K6NA QSO (San Diego): 1555Z. K6NA left the shack, with ZS4TX still copiable: 1625Z. ZS4TX sunset: after 1700Z."
Glenn mentions the antennas used at each location:
K6NA San Diego: 2 el wire Yagi horizontal flat-top at 128 feet oriented SW for longpath.
W6KW Redding: 3 el rotatable Yagi at 165 feet.
K7ZV Oregon: 3 el rotatable Yagi at 130 feet.
W6OG-Oroville, CA and ZS6CCY-400 miles north of Cape Town: 4-square vertical arrays.
ZS4TX: 2 EL rotatable Yagi at 100 feet.
He goes on to say, "ZS6HA may have had a horizontal rotary also. All other ZS who commented said they had dipoles or low dipoles. K6NA, W6KW and K7ZV received 9+ reports from ZS4TX, while W6OG received S7 to S8. A couple of Californians with average-height dipoles successfully made contacts."
Glenn closes by saying, "This little extended opening on 75m longpath was very interesting to experience for the first time. Although I can't explain the mechanism, due to my long-time activity on 75/80m I can state that this was an extremely rare event and thought you might find it of interest."
Peter Dalton, W6KW commented, "The first ZS/West Coast QSO long path took place 3 years ago between ZS6CCY who answered my CQ at approximately 1435 one October, and continued to build in Strength for the next 20 minutes. ZS6CCY worked only one other West Coast station that day, N7UA. We have had several other openings to ZS since then, but NONE the likes of this past one on November 10."
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For more information concerning radio propagation, see the ARRL Technical Information Service 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/.
Sunspot numbers for November 15 through 21 were 0, 13, 13, 0, 0, 0 and 0 with a mean of 3.7. 10.7 cm flux was 69.2, 70.6, 69.8, 68.8, 69.5, 69.7, and 69.1 with a mean of 69.5. Estimated planetary A indices were 5, 6, 5, 2, 3, 28 and 13 with a mean of 8.9 Estimated mid-latitude A indices were 5, 5, 5, 1, 2, 10 and 9, with a mean of 5.3.