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Spring 2009 Issue |
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Was It E Skip or Tropo? |
Computer propagation
sites have all but replaced 10-meter band-opening alerts. |
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At the SEA-PAC convention in Seaside, Oregon in June, several 6-meter operators were recounting their recent tropo contacts with KH7Y in Hawaii. “I have never heard the tropo between Oregon and Hawaii as strong as it was over this 2500-mile path. At one point, Hawaii was coming in well over S9 for about 10 minutes,” commented an Extra Class ham, obviously mistaking the double-hop E skip band condition for the summertime California to Hawaii tropo openings. “I live just north of Dallas, and the Florida FM 2-meter repeater gave us a skip opening that lasted for a solid day!” remembered another ham, mistaking a likely tropo opening for short-lived summertime E skip. Yet another ham commented, “It was like a rollercoaster. The signal was strong, then would take a momentary deep fade, and then the tropo would build back up again, cycling this way, over and over.” Nope, not tropo.
Ken Neubeck, WB2AMU, author of the book Six
Meters, A Guide to the Magic Band, describes E skip as regularly cycling
strong to near disappearing signals within a 30-second time frame, and
tropospheric ducting as moderately strong signals with gradual build-up
and decay for hours on end. Sometimes tropo conditions will lead to
moderately strong signals for days on end! Good news! Sporadic-E skip occurs twice a year, no matter where we are in the 11-year solar cycle. As we just begin the climb of solar Cycle 24, sporadic-E VHF/UHF excitement may be just as strong now as it will be six years from now.
The E-layer of the ionosphere energizes every
day at about 50 miles up. Sporadic-E VHF/UHF propagation takes place when
radio signals reflect off drifting clouds of highly ionized E-layer
particles, slowly moving from west to east. The reflections on VHF and UHF
frequencies may be so “spot” intense that you may hear a station 1400
miles away, but your friend 10 miles away hears nothing! A few minutes
later, you may hear your friend working sky-wave stations, and this time
you hear nothing! Welcome to E-skip! |
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