I heard a long-delayed echo in the 2001 CQWW SSB contest. I was
operating on 15 meters and was calling CQ with a three-high stack of
monoband yagis. I was calling a live CQ (not a DVK recording) and
heard the last seven syllables (approximately one and a half to two seconds
delay) of what I had just said echo back. It did not sound like it could have
been someone simply recording it and playing it back, as the echo was
already happening when I stopped transmitting. It wasn't weak - I was
so startled I didn't think to look at the S meter, but I'm guess it was
no weaker than S3. There was no obvious Doppler shift on the signal.
I only heard it once, and it has never happened again.
I have a lot of experience hearing backscatter echoes of my own
signal, and I have also had someone record my DVK message and replay it
on-air (which I agree is a weird and amusing experience.) The LDE I
heard was qualitatively different from those more commonplace events.
I was interested enough to look up what I could on the subject, and
found that there have actually been quite a few QST articles on the
subject of LDEs, especially from 1969-1980. The first QST article on the
subject appeared in August, 1934. I put together a brief presentation
for a local club meeting:
http://www.wm5r.org/presentations/lde/
(Yes, I know the images are broken.) I probably should have put
in footnotes on each slide, but I did include a bibliography at the end.
It's not a really stellar slide show, I admit.
My personal favorite theories are that (a) it's all in my head, (b)
the 138ms Periodicity Theory that a duct forms in which the signal
travels around and around the planet until it escapes back to earth, and
(c) inadvertent HF EME (although the lack of Doppler shift in my
experience makes it unlikely.)
On Wed, Jan 14, 2004 at 06:28:21AM -0600, W5PR wrote:
>
> I'll have to admit that I have done a LOT of work on 10 meters in the last
> 47 years, including many contests (W5PR, KZ5MM, KE5FI, WA5IHS, DL4FQ etc)
> and I have never heard an echo longer than about half a second. I HAVE had
> people record me and play it back. (Which is both weird and amusing.)
>
> Take heart though, if you are being "heckled" it means you are loud. It
> comes with the real-estate!
>
> Chuck W5PR
>
> >
> > OK, let's think about it. Radio waves travel at the speed of light,
> > and a 10 second delay would translate to about 1.86 billion miles
> > before it was again heard. That is approximately the distance to the
> > Planet Saturn, or assuming an Earth orbit, a complete round trip 7,410
> > times.
> >
> > You could assume a large dish antenna with 50 db of gain, and a loss
> > of 1 db per trip, and the signal would be in the mud on the 148th
> > trip. That would leave approximately
> > 7262 more trips around the Earth until it was received and heard. Not
> > to mention the vast improvements in receiver noise floor in over 40
> > years.
> >
> > Tape recorders have been around for a long time. So has elementary
> > math. Recorders change with time, math doesn't.
> >
> > In no way do I mean to doubt Zack's word about it, but it simply is
> > not possible as an LDE.
> >
> > On my own recollection of received LDEs the longest I ever heard was
> > the letter B of my call at about 35 wpm, and that was also on 10
> > meters.
> >
> > I leave it to someone else to figure the gain and power needed to
> > bounce a HF signal off Saturn, which is actually twice the distance.
> > Even our best orbiting telescopes are not capable of that.
> >
> > 73
> > Ed
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>
>
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--
----------------------------------------------------------------------------
Kenneth E. Harker "Vox Clamantis in Deserto" kharker@cs.utexas.edu
University of Texas at Austin Amateur Radio Callsign: WM5R
Department of the Computer Sciences Central Texas DX & Contest Club
Taylor Hall TAY 2.124 Maintainer of Linux on Laptops
Austin, TX 78712-1188 USA http://www.cs.utexas.edu/users/kharker/
----------------------------------------------------------------------------
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The world's top contesters battle it out in Finland!
THE OFFICIAL FILM of WRTC 2002 now on professional DVD and VHS!
http://home1.pacific.net.sg/~jamesb/
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