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| It sounded more like Sporadic E than ducting. I've seen more ducting at night than by day from Iowa. One can get really great ducting over a large area that works up through the microwave bands (weather radars show long range echoes with very high intensities) under a large area high pressure dome. Truly weather induced propagation. The air is calm under the high pressure dome, so night time radiant cooling of the earth's surface cools the adjacent air but in the calm there's no circulation to mix it and that temperature inversion (warmer aloft than on the ground) causes greater than normal refraction of radio (and probably light waves leading to more UFO sightings) waves at VHF and higher frequencies. Ducts can form with tops and bottoms, once I had great contacts with NY and PA from IA but stations in Indiana couldn't hear the stations out east because they were under the duct. There is an ocean duct that forms nearly every year from southern CA to Hawaii. At the CA end the top of the duct is visible on the mountain faces.
Temperature inversions would form every night, strongest in the early morning if the lower atmosphere wasn't mixed by winds. Often VHF propagation is longer of early mornings anyway. Propagation is poorest when its windy to keep the lower atmosphere more uniform.
6M SSB was hopping, it will be hopping this afternoon whether there's good propagation or not from the ARRL June VHF contest that begins at 18Z and runs to 3Z Sunday. But we hope for good sporadic E or some ducts. My antenna is a dipole in the garage attic. I'll do better in the future.
Gerald J., K0CQ | |
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Radio anomaly...weather?
