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Monday, July 9, 2007

more long-delayed echo e-mail

This week’s Surfin about long-delayed echoes has generated additional interesting e-mail today.

David Burger, VK2CZ, wrote:
I enjoyed your summary of LDE info, including the Oslo summary too... I've been licensed here in Australia since 1974 and have encountered LDE's around 1977 / 1978 on the 15m band during my degree course. In more recent times, I currently use a 'very very ' large 10m antenna array and have encountered LDE's on some DX stations (VE2 and western EU) from here over the past 6 years or so... ie not my own echo's, but delays between the DX main signal and then replications of their signals.. These type of signals were last heard in Dec'06 during the ARRL 10m contest I did -->> [ note: I didn't describe the signals however, but you can see what I've done]

Being an engineer (PE) with a very pragmatic & practical bent... I simply put this down to the effects of signal progression in a waveguide - where it is possible to have a signal moving through a waveguide down to 1% to 2% of the speed of light or less... These are all classical worked examples in microwave handbooks... where the signal frequency is near the cut-off frequency limit for a waveguide...

But I am very very confident the ionosphere can 'fabricate' a sizable waveguide style duct over short periods... and while this would and could explain a single signal delay, some discontinuity in the 'ionospheric waveguide' could generate return loss blips... hence echo's. I've no way to 'test' this idea.. but maybe info from ionosondes might help explore it..

Anyway, I figured I'd share my idea with you... as I sort of took this for granted for the past 25 years that every engineering student who studied microwaves could see this effect if practice on HF.

The idea of unknown aliens or X-Files may appeal to some, but after being immersed in engineering forensics for many years, most things can be explained.. anyway - it makes sense to me..

Sverre Holm, LA3ZA, responded to David and carbon-copied me:
Thanks for your interesting info on possible LDE's. I have never heard any myself, except for the echoes I describe on

Here I have recorded JA3YBK coming in simultaneously over three different paths which most likely are short-path, long-path, and short-path w/ extra trip around the earth. Of course this is not an LDE, but rather short-delayed echoes, but they are still interesting.

Terry Glagowski, W1TR, also e-mailed me today with the following:
I had the experience of an LDE back in the mid 1990's maybe about 1994 or 1995…

I was located in Spokane, WA and it was late evening, not quite midnight…

I was talking to some W6 and W7 stations in CA, OR, WA on 160 meters and I heard the LDE echo on my own transmission… about 1/3 second.

I also tried it on 75 meters and the same thing happened!

The other stations I was talking to could not hear anything on my signal or theirs...

This went on for about an hour, and then dissappeared altogether and I have never observed it since !

I wrote a letter / email to ARRL describing this (tech dept) and several possible explanations were given from different articles available at the time… The most likely, that my signal followed a discontinuity in the magnetic flux lines down to the southern hemisphere and bounced back from there.

That would explain the time of 1/3 second, but I didn't do sufficiently precise or formal recordings / documentation of the phenomenon to go any further with it… too bad! There was no perceptable doppler shift that I could discern.

Finally, Whitey Doherty, K1VV, wrote:
Another excellent posting... We have experienced LDEs in several contests ... our sigs on CW coming around 1/7 of a second later ... confused me the first time I heard it ... we have worked some DX during contests that the same thing happened ... it seemed like their CW sign was coming from several directions at once...with delays .. almost impossible to copy the CW ...

I remember hearing about an LDE incident many years ago ... must be at least 40 years ago ... when TV channels went off the air at midnight .. Some one ... don't recall where it said a program showed up on the screen .. snowy picture ... but it was a broadcast from 6 years previously lasted several minutes ... can't recall where or exactly when I heard that or read it.

I replied to Whitey that I thought I had read about it in one of Frank Edward's Stranger Than... books.

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