Friday, November 27, 2009

Around the world in milli-seconds

Today, I was listening to ST2AR (Sudan) on 17 meters at 1600 UTC, working a nice pileup.

Something was weird about his signal, though. At first I thought it was flutter, but that's ridiculous - the path is 080 short path. Then I thought someone was intentionally interfering. But it was simultaneous; started as son as he started, and ended immediately after he ended. Fast CW, no way it was intentional interferece...too closely timed.

Then it hit me; I was receiving short path AND long path AT THE SAME TIME! Never would happen with a directional antenna, but I was using the off-center-fed dipole at 64 feet. I was hearing BOTH signals at the same time, the long-path one just barely delayed and sounding like interference!

5798 miles short path, long pah 15782 miles. I listened for a few minutes and was fascinated! I had never heard this before, at least not that I could recall!

At about 1615 UTC, the short path took over and the interfering long path signal decreased quickly until it was gone.

Using some quick calculations, the time to trave short path is 31.2 msec. Long path is 84.5 msec. That would explain the noticeable overlap.

Wow, propagation never ceases to amaze me.

73 and good DX!

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