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KP3FT
01-27-2006, 11:45 AM
Hi all,
# # Recently I've read about the LDE (Long Delay Echo) effect, and am wondering how many hams here have personally experienced this. #If so, when did it happen, how long was the delay and how strong was the signal?
# # There's a lot of info about it; it was first noticed around 1927 and there have been many reports since then. #It's basically hearing your own (or other's) transmissions echo back after you stop transmitting, anywhere from a couple seconds to many minutes of delay. #Many theories abound about it, including multiple long-path revolutions, and the radio wave "trapped" in atmoshpere layer and coming out later, and pranksters recording and re-transmitting (impossible in some cases), and the radio wave bouncing off a distant object in space like "plasma clouds" near the sun. #
73!
de Jeff KP3FT

AE4FA
01-27-2006, 12:11 PM
I've experienced it. Several years back, while calling a station in Mauritius, I heard my fist sending my call about 2 seconds after I sent it. Got the Mauritius station, by the way.

KI4NGN
01-27-2006, 12:59 PM
I have no doubt (seriously) that the phenomena exists, but it is so incredible to think about. Considering that an RF signal travels at the speed of light, that means for you to have received your code signal a couple of seconds after you sent it, it made a 372,000 mile round trip. Given that the circumference of the earth is ~25,000 miles, that is quite a feat! Amazing. http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

AG3Y
01-27-2006, 03:11 PM
With todays technology, and the number of hams using soundcards in their stations, it would be so very easy to make a quick recording of someone, and transmit it back to him a few seconds after he un-keyed his transmitter.

But I remember reading and hearing about LDE many years ago, long before such devices were even heard of, much less common !

Interesting phenomena, to say the least !

W5HTW
01-27-2006, 03:24 PM
LDEs are still unexplained, but the most likely cause is trophospheric ducting. In fact, tropho scatter is a sort of cousin of the LDE. I have heard one back in the 1960s, from a government station I was operating. I think I'll put the story on my web site, (in a few days!) since this subject keeps coming up.

The only serious investigation of them I have heard of was from the Physics Lab at Stanford University, in the 1960s. Because they are rare, and serve no known purpose, no money appears available for further study.

It is generally believed they are far more common, though, than originally thought, but simply aren't recognized as such when they occur.

To those of us who have heard one, they are a curiosity, a natural, but yet unexplained, phenomena. While most of us think in terms of ham radio, the one I experienced was on government HF radio, and I have heard of others in the HF frequencies, but not in ham bands.

Ed

WA9CWX
01-27-2006, 03:29 PM
I too heard an LDE, CW, either late 74 or up to 76.
( I remember the house I lived in, just not the DATE)

I am pretty sure 20 meters. The delay was VERY confusing to me, actually freaked me out a bit. It was about 2 or 3 seconds long, as I recall, no doppler shifting, just right on frequency, no 'worrble' or any other multi/long path type signs. Also fairly loud. I 'tested' it several times, YUP, it was ME, V E R Y strange.

Where 'WAS' it ?? And WHY and HOW did it come back.....?

ACTUALLY, there are so MANY unexplained things that have excellent documentation, IF you go looking for them, it really does seem that the predictable, orginized, law abiding physical world is more of a convention and convenience than a reality.

w8cbc
01-27-2006, 03:32 PM
I heard one in 17 metres last October, about 90 seconds delayed. A complete 30 sec. transmission of mine came back, fading down at the end. I think it was someone with a recording device.

That 751A sure sounds good though. http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif

KL7AJ
01-27-2006, 05:55 PM
The most plausible explanation for LDEs to date is plasma mode conversions. Electromagnetic waves are converted into ion acoustic waves in the ionosphere, and then back to electromagnetic waves. Ion acoustic waves travel at only a few times the speed of sound....a long path could easily show a delay of 10-20 seconds.

Although conditions necessary to create these dual mode conversions are rare in the ionosphere, they can be consistently reproduced in controlled plasma chambers.


eric

w8cbc
01-28-2006, 12:42 AM
That was the other possibility for mine - it may have been you who clued me in about plasma transduction - it's a fascinating concept!

w8wlc
01-28-2006, 01:27 AM
I heard my own fist via LDE back in 1976 on ten meters. At first I thought someone was messing around with me

G8ADD
01-30-2006, 01:12 PM
Back in the early 60's I was monitoring solar activity by making daily signal strength measurements of MSF (Rugby, UK, standard time and frequency service) and found that there were quite frequently at least one echo at a time delay of about a quarter of a second, and sometimes multiple echoes. The beep at minute intervals enabled me to determine that these echoes could occasionally be delayed by over a second.

I understand that a favoured theory for these shorter delayed echoes is that the signals follow the Earth's magnetic field and are reflected in the southern hemisphere and come back to near their starting point. This effect is best heard about 2.5 MHz. I have never heard very long delay echoes but people I respect claim to have heard them so I accept that they probably exist.

73

Brian G8ADD

WA5SWD
07-15-2010, 04:13 PM
I also have heard my own signal as a Long Delay Echo. I was in a SSB QSO
and turned it over to the other station with the word 'Over' and immediately
unkeyed the mike. I then heard my own voice say 'Over'. There was no
distortion on the signal, exactly on frequency but with normal atmospheric
background noise. The Rig I was using was a Drake TR4, not known for
extreme sensitivity, most likely about 5 uV as a minimum detectable signal.
I would estimate the echo was about 75 uV but that is a SWAG only.
I freaked out and instantly shut the rig down. I had never heard of LDE's
before and it frankly frightened me, with the normal adrenalin reaction. One
does not expect ones radio to start talking back in your own voice! It has
never happened again although I have operated VHF a lot more than HF over
the last few decades.

K0RGR
07-15-2010, 05:01 PM
Yes, O.G. Villard Jr., W6QYT a Stanford professor and founder of SRI, did a lot of work on LDE's.

I have heard the kind that may be explained by ducting in the magentosphere, where you hear the last part of a character you've sent - a delay of a few hundred milliseconds.

W4SUL
07-15-2010, 09:59 PM
This entire thread is a long delay echo :p

I have indeed heard myself come back when using full break-in cw a couple of times.

N0SYA
07-17-2010, 01:14 PM
so would this count for a contact in was or a ct or something??

AD5MB
07-17-2010, 01:52 PM
pranksters recording and re-transmitting

that would be the first thought that would pop into the head of a skeptic

on further thought, it's just silly. how many times would you have to do it before anybody noticed? how would you know? why would you care? what problem are you solving?

indicating that some ( many ) skeptics would benefit from a tuneup of their thought process.

K0MU
07-17-2010, 04:38 PM
Late 80s I think this occurred to me.

I was living in Duluth, MN at the time and had a contact with someone in Thunder Bay, ON. His signal pinned my meter. Thunder Bay is about 150 miles from Duluth.

Another person joined from Minneapolis, MN. He is about 150 miles south of Duluth. He also pinned the meter.

The Thunder Bay station and MPLS station were also pinning the meters to each other.

And this was on 20 meters! (really short skip for 20)

After the contact was over, I said 73, etc and then the echos began.

The delays were about 5 seconds. The echo was perfect and in tune. I thought there was a joker with a tape recorder but I moved my VFO slightly and transmitted a really short test. The echo came back perfectly in tune 5 seconds later. I repeated this several times and the echo came back perfectly in tune.

My conclusion was there was it was natural with the aforementioned "short skip on 20 meters" with the pinned meters and that no one could possibly track my VFO changes perfectly and operate a tape recorder.

It was just amazing.

The plasma acoustic wave theory mentioned earlier seems interesting

73 73 73 73 73 73 73

SV9OFO
07-18-2010, 12:02 AM
So, we can safely exclude all possibilities of the reflector being some asteroid being close to earth?

no QSB no doppler no tape no nothing, just the acoustic wave theory and the asteroid. The acoustic leaves to be proven, the asteroid would require several KWatts EIRP to pop.

An enormous fraction of the power emitted from an antenna always flees out of the ionosphere to space, This is definate. Who would run the free space equations for a signal path of one and the half million km's?

I did for 100W and 1,5Mil. KM's and an antenna of 15 dBi and I found some interesting results... s0 but audible running 100watts.

Still, the acoustic wave solves the problem of echoes of near 15 secs to 3 minutes.

NY7Q
07-18-2010, 12:41 AM
:eek:Back in the 50s(early) we experienced it aboard ship and often spoke to each other about it at the time.
It was weird.

W5HTW
07-18-2010, 01:07 AM
This old thread has popped up again, so I'll comment.

I have never heard LDEs on amateur radio, but I have seen many reports of them, with delays of a couple of seconds, a few seconds, even a minute.

My one experience was in government HF radio. We ran a CW tape, one minute long at 18 wpm, on our net control frequencies. Then we went on speaker monitor for one minute. Three receivers, all at high volume, so we could hear them while we were away from the operating position doing other things.

Our tape consisted of VVV VVV VVV DE CALL CALL CALL repeated three times, then ending with QSX information.

Two of us on duty, both of us away from the radios. The VVV had completed and there was nothing but noise on the three frequencies. Then suddenly I heard our call sign. It was repeated perhaps twice, then the VVV portion started. It did not finish. The whole thing lasted maybe 7 or 8 seconds.

I dashed to the operating position thinking someone was calling us. Then it dawned on me, I had heard the VVV part. Weird? It was not a complete transmission.

I monitored for a few minutes, but I let the tape continue to do its one minute thing. No further transmissions were heard.

It was on frequency, no Doppler. It had no fading. It started suddenly, stopped suddenly. Since we were monitoring three frequencies I can't say which one of them it was on. One was in the 6 mhz range, one in the 10 mhz range and one in the 13 mhz range. I'd guess it was on the 13 mhz, but that is only a guess. It was at our precise speed, no variation. It was indeed our signal coming back to us. I do not remember now if this was at night, but since only two of us were on duty, it was either an evening or a weekend, with minimum crew.

This was not in the USA. It was no prank, no one recording the signal.

The delay between the end of our automatic transmission and the start of the LDE was quite long, perhaps ten seconds, maybe a bit longer.

This is the only LDE I ever heard.

Later I responded to the Stanford U request for information on LDEs, and gave them my report. I never heard anything from them except a brief thank you.

There is a theory these are signals bounced off a passing asteroid. However, since there is no Doppler shift, that seems very unlikely. The signal I heard was dead on frequency and remained so. The delay was very long, too long for normal round-the-world echos.

The start, stop and duration suggests some natural phenomena we do not yet understand, and it doesn't occur often enough we can examine it. One theory is ducting around the planet, over and over, until the signal breaks out of the 'duct' and returns to earth. It did not 'fade in,' and it did not 'fade out.' It was as if a switch was thrown. It was turned on, then it was turned off.

The question that would arise in my mind is this. Is the signal being returned to earth continuously, but from a 'moving source' so that it is heard only briefly at any one point? In other words, the LDE I heard could have been heard somewhere else a half second later, and then still further around the world. Is the return so narrow it is heard in a range of only a mile or so? Then perhaps years later, heard in a different mile in a different location?

If only we could create the effect at will! There isn't enough interest in them, though, to make that happen. To my knowledge no one is studying them. They simply happen.

By the way, my LDE was in 1968, in the Far East.

Ed

...

SV9OFO
07-18-2010, 02:20 AM
ahem. Here, I must remind you that doppler shift is nearly inexistent in HF.

Check AO 07 Beacon (http://www.amsat.org/amsat-new/tools/predict/) at 29.502 and see what I am talking about.

(sigh. It works only while in daylight)

KU4GW
07-18-2010, 12:47 PM
I had this happen to me for the first time in 14 years on ham radio just recently on 30 meter CW on 10.120. It's been about 3 months ago, forget the exact date and time, but I was in QSO with another SKCC station and at first I thought someone was being a wise guy and sending on top of me. I was working full break-in and after a few seconds I realized the person whom I thought was sending on top of me was sending the exact same characters I was, but only a split second after I did. For example when I sent dit dah dit dit for the letter L I heard the echo by the time I sent the first 2 characters dit dah of the letter L and then heard them repeat everything I sent. Really weird experience, but like I said, it was the first time and the only time I've experienced it in 14 years. Also, the echo didn't last very long before it faded away.

KA4DPO
07-18-2010, 02:24 PM
We used to do loop back transmissions over satellites. It was fun to hear your voice come back to you with a half second delay.

WA9CWX
07-21-2010, 11:33 PM
:DAgain, I will re-state something that we all seem to forget.
The number of truely strange, 'non-typical' physical events out there that have been well documented is astounding.
What usually happens, howeer, is that they do not fit the basic physical landscape as understood by people in those fields, so they tend to NOT get press, so to speak. Still, any serious investigation will reveal a huge underground 'reality' filled with not-readily-explained phenomena.

I was amazed fairly recently to discover a huge number of seriously reported UFO sightings over a large expanse of the USA, from the late 1880's to early 1890's.

There are seeds from crops that seem to appear where no winds or other mechanisms for travel can explain their presence, animal remains, well documented, where they can not logically exist. Many such phenomena, Long delayed echos are just one more in line, waiting for the heavenly saddist to explain to us some day!!:D

KA4DPO
07-25-2010, 01:55 PM
:DAgain, I will re-state something that we all seem to forget.
The number of truely strange, 'non-typical' physical events out there that have been well documented is astounding.
What usually happens, howeer, is that they do not fit the basic physical landscape as understood by people in those fields, so they tend to NOT get press, so to speak. Still, any serious investigation will reveal a huge underground 'reality' filled with not-readily-explained phenomena.

I was amazed fairly recently to discover a huge number of seriously reported UFO sightings over a large expanse of the USA, from the late 1880's to early 1890's.

There are seeds from crops that seem to appear where no winds or other mechanisms for travel can explain their presence, animal remains, well documented, where they can not logically exist. Many such phenomena, Long delayed echos are just one more in line, waiting for the heavenly saddist to explain to us some day!!:D

Those were secret hot air balloon flights being conducted at area 49.:p:D

N0WYO
07-25-2010, 04:44 PM
Those were secret hot air balloon flights being conducted at area 49.:p:D


ALIENS....THEY'RE TALKING BACK TO US...:D

NL7W
07-25-2010, 06:42 PM
We used to do loop back transmissions over satellites. It was fun to hear your voice come back to you with a half second delay.

The round trip time for geo-sync satellite comms is approximately 530 milliseconds... no LDE there! :D

M0WAN
07-25-2010, 07:56 PM
I recall reading a book where amongst other dodgy goings-ons, long-delayed echoes were discussed - time delays of 30 seconds to several minutes were apparently well documented in the earlier days of radio.

One suggestion (besides magnetosphere ducting and others) was the remote possibility that maybe there was an ancient satellite in orbit placed there by an alien race, with the sole purpose of detecting when we became advanced enough to generate radio signals.

It was proposed the satellite(s) would then indicate its presence by receiving radio signals, delaying them by an unnatural amount then re-transmitting them. Humans would then search for the satellite and reap the technical wonders contained therein.

Of course, we are so full of ourselves and the belief that we know it all that the delays were never properly investigated, and now it is too late as the place is swamped with radio signals and the poor old delay probes can no longer function as designed.

OK, but what if this wasn't actually too wide of the mark?
Who are we to call this nonesense?
History is full of daft ideas that actually turned out to be correct.

W5HTW
07-25-2010, 09:23 PM
I recall reading a book where amongst other dodgy goings-ons, long-delayed echoes were discussed - time delays of 30 seconds to several minutes were apparently well documented in the earlier days of radio.

One suggestion (besides magnetosphere ducting and others) was the remote possibility that maybe there was an ancient satellite in orbit placed there by an alien race, with the sole purpose of detecting when we became advanced enough to generate radio signals.

It was proposed the satellite(s) would then indicate its presence by receiving radio signals, delaying them by an unnatural amount then re-transmitting them. Humans would then search for the satellite and reap the technical wonders contained therein.

Of course, we are so full of ourselves and the belief that we know it all that the delays were never properly investigated, and now it is too late as the place is swamped with radio signals and the poor old delay probes can no longer function as designed.

OK, but what if this wasn't actually too wide of the mark?
Who are we to call this nonesense?
History is full of daft ideas that actually turned out to be correct.



This was the theme of the original short story, "The Sentinel." That story was made into the movie, but it began as a pyramid type monument on our moon. It had been there for untold eons, waiting for someone or something to touch it. Astronauts did, and it then sent a signal back to its home civilization that it had been found. It was, of course, pure fiction.

Some of the books written about LDEs were of the Edgar Cayce variety, way out. Some of the stories allegedly found portions of radio broadcasts from 20 or 30 years earlier suddenly being heard again, from long-dead radio stations. That would have made good fiction, but there were never any substantiated reports of such.

The one I heard, described earlier in this thread, was a 'long delay.' When I heard the echo, I had left the radio monitor position, and had walked back to our TTY tape relay position, and had already started working there. So the delay had to be a minimum of 20 seconds before it started, and could have been up to 30 seconds.

But something occurs to me. We were making automated one minute transmissions, then on speaker monitor for one minute, until the next transmission started. Who is to say the echo I heard was not from an earlier transmission?! It could have been hours, or even days delay! But I accept it as being a 20 to 30 second delay.

We shall never know. What is puzzling is the returned echo had no fade. It did not 'fade in' and it did not 'fade out.' Suddenly it was there, steady and stable, and then suddenly it was gone. No signs of unusual atmospheric noise which may would result from some sort of ducting.

At that time, though, we were using tropo scatter operations for very reliable RTTY. Not on these transmitters, but on other systems. Troposphere scatter long range comm systems were in the low VHF range, though, and not HF. However, they could create a similar effect, I would think. We had no way of monitoring the scatter systems. What if there is an "HF scatter" that sends the waves along many multiple paths? I do not think we know everything about propagation yet.

ed

M0WAN
07-26-2010, 09:47 PM
I'm sure you are right - there is much to learn about the rarer modes of propagation, but 30 seconds delay or longer? Surely there would be audible artifacts present on such a well-travelled wave?

One problem I have with the Bracewell probe theory outlined in my previous post is that as the frequencies involved were HF or lower, surely the ionosphere would have blocked much of the signal, both to and from the probe?

I'd like a definitive explanation of the phenomenon, but I dare say no-one can really offer a water-tight theory, at least not yet.

W0IS
07-26-2010, 10:03 PM
One problem I have with the Bracewell probe theory outlined in my previous post is that as the frequencies involved were HF or lower, surely the ionosphere would have blocked much of the signal, both to and from the probe?

That problem is easily solved. The repeater is not located aboard a satellite. It's located at a terrestrial location, at one of the Secret Alien Bases.

KP4MD
08-23-2010, 01:17 AM
Long Delayed Echoes were heard today 22 Aug 2010 at 2120 UTC in my PSK31 transmissions with 9A5LO/P on 18.100 MHz (Sacramento, California to Croatia circuit). The propagation was just starting to open to Europe with much deep slow signal fading. 9A5LO/P was received about 30-40 Hz up from my transmitted frequency. I heard Long Delayed Echoes after 2-3 of my transmissions, delayed about 2-3 seconds and also shifted about 30-40 Hz higher than my transmitted frequency. My transmitter power was 40 watts to a base loaded vertical antenna. I remember hearing long delayed echoes on one other occasion about 20-30 years ago. de W6/KP4MD

WR8D
08-24-2010, 02:33 PM
Back in the early 80's Mike EA3OT in Spain recorded the delay between him working stations long path and direct path. Many of us working him then got to listen to the recordings he had made with sometimes several seconds of lag in the signals. 14.200 was his freq, we used him as a band barometer. If we heard Mike blasting in stateside we knew the band was open.

Legends lived in the 80's on amateur radio. Dang, what a time it was for radio!

--... ...-- WR8D

G0GQK
08-24-2010, 09:46 PM
I heard what I thought was my voice calling CQ in 1987, I couldn't believe I heard myself and I thought somebody was messing about.

G0GQK

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