Ref. to (a) above - Anybody here heard 'round the world echo on 20 Meters ?
Often in the past, and several times recently. I even have some recordings of it around someplace, including SDR recordings that allow you to see it happening on multiple stations.
The most interesting echo or delay I have ever seen happened a couple of years ago on 80M. Conditions were extremely long and a few of us noticed very, very, heavy echos on each others transmissions, far heavier and longer than I have ever heard on 20M. Playing around I found that I could slap the desk mic switch making a very audible "crack" during a very short transmission. I could hear my own "crack" echoing back, like a radar pulse. At times I could hear multiple copies echoing back. Unfortunately I got no recordings of that, it would have been very interesting to measure the delay. I am convinced the delay was possibly more than the ~135 msec max of circling the Earth at the longest distance. While only a guess, as no measurements were taken, it felt closer to half a second.
Interesting observations ... I've only heard personally the phenom on 20 M some years back ...
This last winter 80 Meters got really, really long on a regular basis, the time station from S. America on 8410, as noted here, was easily heard:
http://www.hfunderground.com/board/index.php/topic,823.0.html... but no long distance echo effects were observed/heard.
On the subject of LDE (Long Duration Echoes), here's some info on Wikipedia I had not seen before and so I'll post a link (so I can come back later and do some deeper reading when I have time too):
http://en.wikipedia.org/wiki/Long_delayed_echoAnd another personal observation from an individual, with his own theories, perhaps a bit outside the 'mainstream' view, but hey, that's how science progresses (observe a phenomenon, propose a hypothesis, prove it or disprove it and possibly it becomes a theory):
http://www.eskimo.com/~nanook/radio/2006/12/long-delayed-echo-radio-phenomena.html
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