Long delayed echoes

The following discussion about the long delayed echoes (LDE's) on the EME signals took place in the Moon-Net reflector. I found the subject so interesting that I decided to put together all the messages in this page.

The page is sorted chronologically, from oldest to newest contributions.

On 8-Apr-1998 EA5GIY wrote:
Hi Joan-Miquel EA3ADW and Rich NJ1A!

I have posted the answers to your questions on this reflector because I'm sure that other eme fellows have had the same experience and it would be very interesting to hear them.

Computer was running AF9Y FFTDSP at that time. I should have looked at the screen to see signal strength and Doppler. I didn't. I was so surprised that I just sat back for a moment, looking at my transceiver with wide opened eyes, trying to figure out what had happened! Then I choosed a clear frequency and tried for a while to get the same echos.
No way!

On 8-Apr-1998 KV6J wrote:
Aloha All

     I decided not to say anything.  When it happened I was all caught up in the contest and dismissed it as wierd and didn't even make a note.

    Eric's comments sounded so exact.  The same thing happened to me about two hours later.  It was the first time that session that I'd heard an echo but I heard two of them.  I heard k k  k k.  The first k was partial and there was a slight pause between two and three.  I checked and my Tx delay will not let me hear k k k k even if I sent four (I'm sure that I didn't).  The only difference is that my 'second echo' was barely louder than the first.

     Now that I've stirred up some old brain cells wasn't there something in QST, 30-40 years ago about long delay echos on HF?

On 8-Apr-1998 Ken Arck wrote:
I remember seeing an article about LDE's too way back when. As I remember, they tried to show a causal relationship to multiple trips around the world as the source.

Now, figuring roughly 2.5 seconds to tranverse ~500K miles to the moon and back versus how many trips around the earth to cause even a longer delay... I'd be REAL interested in how to reduce loss over THAT kind of TE propogation :)

On 10-Apr-1998 PE1OGF wrote:
About the long delayed echoes.. If you were answereing a CQ couldn't it be possible you were together with another station answering at the same time. In these days we have very acurate clocks so TX Sequencing of you and the other station could be the same perhaps half a second delay.. If he also sended  K K on the end you copied his and your echo.. what about that?? I don't belive in the long delayed echoes like on shortwave bands.. this is VHF !!!

On 10-Apr-1998 EA5GIY wrote:
Since what happened during Dubus, I have been trying to find references of similar experiences. I just found the following:

In G3SEK "VHF/UHF Book" (a very very good book!), page 2-63, Ian says:

" Rare but well-documented cases of echoes being heard with much longer delays than the 2,5 second earth-moon-earth path have been recorded by stations carrying out EME tests....As far as I am aware, no credible explanation has yet been put forward for long-delayed echoes on VHF/UHF."

Interesting enough, is that it happened to Bill and myself with a 2 hours interval...

On 10-Apr-1998 EA5GIY wrote:
G3SEK, in his "VHF/UHF Book", refers to a paper written by OZ9CR: "Ghost Echoes on the Earth-moon Path" - Nature, september 4, 1975, page 36.

On 10-Apr-1998 GM4JJJ wrote:
Is it possible that what was being heard was another station that was testing or sending on the same frequency?

On 10-Apr-1998 EA5GIY wrote:
It is of course possible. but the 2 dits had a long separation between them, and I received them EXACTLY as they were sent.

On 10-Apr-1998 GM4JJJ wrote:
It struck me that what you might have heard is just someone doing the normal thing of sending dit dit back to you at the end of the QSO.

The KK KK that Graham reports does sound exactly like another QSO going on, particularly since you both said that these LDE were louder than you own normal echoes, which you had hardly been hearing at all.

I think the coincidence that we got two reports around the same time is not too surprising given that there was a contest going on and there were at times a number of stations calling on the same frequency.

We need some more evidence (ie a recording) that we can analyse to see what the real delay was and what the doppler was.

I'm sorry but 2 dots can sound pretty much like any other 2 dots...

On 10-Apr-1998 G3SEK wrote:
Actually it was Geoff, G3NAQ who wrote that chapter. The reference he cites from OZ9CR is very persuasive. This was on 1.3GHz, way back in 1975, so the   possibility of another station being involved seems even less likely than a LDE.

On 10-Apr-1998 GM4JJJ wrote:
These new fangled DSP filters have a lot to answer for - their processing delay times can be quite long :-)

On 10-Apr-1998 K3PGP wrote:
I have a very well documented case of this that occurred to me back in the 70's. on 432 MHz.  I observed this event more than once and just happened to be set up for it when it occurred again.  In my case QRM from another station was ruled out as it was heard more than once over a period of several days.  Similar events were observed several more times over a period of years.

At one time I had a strip chart recording of one of the events, plus an audio tape.   The strip chart was published in QST and the K2UYH Newsletter along with a description of the event.  Unfortunately that was over 20 years ago and I don't know exactly where all that stuff is today but I'll look around for it as I think it's something that would make interesting reading on my web site.  I know I still have this stuff somewhere!

Here's what I remember of the event:

Both the normal EME echo plus the LDE could be heard on the tape. However, the 'normal' echo was weaker than usual and the LDE was stronger than the 'normal' (first) echo!   The second echo had more doppler shift than the first echo (in the same direction) and more delay than the first echo.  I don't remember at this point if they were exactly double or not. If someone can find the QST article (let me know the issue!) they could derive the exact delay then use their computer to calculate what the
delay for an EME signal should have been at that time.  Unfortunately computers weren't as easy to come by back then so I never did this.  To be honest about it I completely forgot about this until this subject came up here!  The article also had info on the measured doppler of the LDE and should be accurate to 1 Hz or so as I used an audio oscillator and frequency counter to derive this.  The strip chart was done using a narrow band filter tuned to the LDE frequency which reduced (but did NOT eliminate) the outgoing signal (Rx was NOT muted).  The Rx was never completely muted to allow an accurate reference to be recorded on the tape for doppler measurements.   I don't believe the first echo was visible on the strip chart after going through the filter.

I sent all the data off to Stanford University.  No one ever determined the exact cause of this LDE but several interesting theories were proposed.  After studying the data for several months they offered several explanations or perhaps 'best guess' as to what I observed, some of which were plausible, others of which were way out there so to speak!

Summary of letter from Stanford Unv. as I remember it:

You could be hearing a second lunar echo.  You are running enough ERP that is it not out of the question to hear BOTH the first echo off the moon plus a second echo which would be the result of the first echo hitting the earth then bouncing back from the moon.   (This is common at Arecibo, but with a 24 foot dish???)  If this is the case the second echo would have exactly twice the doppler shift and exactly twice the delay of the first echo.  Someone needs to find the QST article then run their
computer program to find out if the doppler and delay are exactly double or not.

Another explanation was a plasma cloud located either behind the moon (but large enough to still be visible from earth) or to one side of the moon but still within the beamwidth of my 24 foot dish running on 432 MHz.  Although somewhat rare these do occur from time to time especially during periods of sunspot activity.  These can be generated when the sun ejects matter toward earth.  There were (and are) several large sun spots being observed over the past couple of weeks along with auroral activity, similar to conditions  when I observed this event back in the 70's.

As far as the 'way out there' explanation, Stanford offered this:  There may be a cosmic repeater  in orbit around the moon placed there by an alien civilization.   In attempt to make it's presence known it picks up whatever radio signal it hears and retransmits them back on the same frequency.  I'll have to admit I don't buy this one, and I was surprised the people at Stanford even mentioned it.  I guess they were trying to come up with any and all explanations and I guess this one was just as
good as any other!

Although it's possible these recent observation could be the result of QRM from other stations, this isn't the first time signals like this have been reported.  To those of you that don't believe in LDE's, you just haven't been in the right place at the right time, as I can assure you that they do exist even on EME circuits and at frequencies at least as high as 432 MHz.  They can be caused by one or more naturally occurring events.  To me the most plausible explanation for someone running EME is the plasma cloud.  Conditions seem very similar to what they were back in the 70's as far as auroral activity and sunspot activity is concerned and I believe what was observed in both cases was most likely caused by a plasma cloud.  Anyone have any tape recordings or exact  observations (doppler and delay) of these recent events?

On 10-Apr-1998 GM4JJJ wrote:
I could buy this plasma cloud idea if there was more than just 2 dots heard by 2 QRP operators, but where are the reports from everyone else who should hear F3VS LDE's all the time?

On 10-Apr-1998 SM5BSZ wrote:
I try to keep a tape recorder running during contest operation so I can listen afterwards. These recordings are nowadays made with a DAT recorder in a bandwidth of about 20kHz. The recording is in stereo and retains full information about all signals and their polarisation.

Because of the discussion about the long delayed echos (?!!) heard by EA5GIY I decided to check if there perhaps was something on my tapes.

Of course there was only about a 50% probability that I was not transmitting myself at the critical moment, Further 144.031 could have been outside my pass band.

BUT the sequence is there AND everything you might like to hear!!

Those of you who are curious, look at: http://sk7do.te.hik.se/homepage/sm5bsz/longecho/signal.htm
There is a spectrum graph and a narrow band audio recording there.

On 10-Apr-1998 GM4JJJ wrote:
Brilliant Leif!

        For those who haven't heard/seen this, the end of the QSO with EA5GIY sending goes exactly as he described, with ..._._ . . then there is a 4.5 second gap before . . by WB5LBT who then goes on to call CQ.

The .. by LBT has a different gap between the two dots to that sent by GIY. 350mS v 550mS

So in _this case_ it looks like the LDE was the other station echoing the final dits back to the sender.

Note:- I still have an open mind on the other LDEs which have been reported over the years and would very much like to see the article that K3PGP wrote in the 70s QST - Does anyone have the reference yet?

There was also so HF LDE article in Radcom recently by G3PLX on Hellschreiber echoes..

On 10-Apr-1998 K2LME wrote:

http://www.arrl.org/tis/bibs/eme.html shows an article

"June QST,  p. 36      Long Delayed Echoes on EME Circuit (TC) 1 page"  in 1976.

On 10-Apr-1998 K3PGP wrote:
I'm in total agreement with this! Especially with a contest going on.   I think I must have missed the original post as I thought more was heard than two dits...  With the help of SM5BSZ I think this mystery may have already been solved.   Tnx Leif!

In my case there was no contest and it was heard more than once.  It definately was my own signal coming back TWICE and at other times once with the wrong delay.    (Around 5 seconds +)  Also QRM wasn't much of a problem back then as there weren't that many EME stations on!  Just to make sure, one time I even remember doing a quick QSY and the weird echo was still there...  I also did a LOT of echo testing on odd ball frequencies like 430.8, 433.6,  or anything other than 432.0 to 432.2 to avoid causing local QRM.

I'd really be interested in any comments once someone locates the original QST article and calculates what the doppler and delay (for one and TWO bounce EME!)  should have been for the day in question..  It should be in the Technical Correspondence section sometime back in the 70's.  Unfortunately my CDROM collection starts in the 80's and my old paper issues are scattered all over the house...  The index I have is useless as it doesn't give any details of the info in the Tech. Corr.
column.  I'm still looking for the letter from Stanford Univ, the original strip chart recording and the cassette tape.  They're buried someplace in 40 + years of collecting junk!!!

PS - I just made a trip outside to inspect the concrete base where the dish was mounted.   Inscribed in the concrete is Oct. 15, 1975 so it had to be after that date.  I also observed this on 144 MHz as well but I believe the case documented in QST was on 432 and occured sometime before 1980.  ?????

On 10-Apr-1998 N7LQ wrote:
I would be interested to know if these LDE are ever heard by the rcving station during an EME QSO as well as the sending station.

On 11-Apr-1998 EA5GIY wrote:
Leif, you are extraordinary!
You have developped fantastic tools for weak signal communications. I was TOTALLY sure I had recognized my 2 dits and, without your recording, I would have been sure of it for the rest of my life! hi! Now I think that the very unusual strenght of the echo (it saturated my audio system) has confused my perception of timing.
I was wrong, and the doubts of David GM4JJJ were right, but my mistake had the merit to open a very interesting debate on this reflector. John K3PGP, I am anxious to read your article!

On 11-Apr-1998 G8MBI wrote:
everytime I read anything on this reflector I seem to get another echoe.

The first is a true reproduction of those things I post.

The second seems to frequently be on the same subject, but is delayed by the time difference between South West France and Hawaii.

Leif, do have a recording..??

David are you sceptical..??

Still it's clearer than shouting "Hello Jimmy" in a Glasgow Pub....and safer..:-)

The second long delay seems to be Mr. gates implimenting 'drag and drop' ..last I heard he was roaming from room to room with his automated 'tracking' tele system frantically trying to follow his progress, switching tele-tubbies on and off as he entered and excited various rooms muttering "how do they do that stuff"..

73 Graham...MAC rules ok.

P.S. I am a real believer in 'LDE' having heard it myself, and also other very strange short 'MS style' pings when monitoring stations at great distance....the first, I dunno....the second I have always put down to random and very rapid transits of sat's in the common volume...

On 11-Apr-1998 GM4JJJ wrote:

The other reference I have found on my ARRL QST CDROM set:-

MAY 1978 p 37-38 Technical Corresponence John Yurek: "Echoes: An Amateur Observation and a Professional Reply"

I can send the .pdf to John if he likes. Just going to print it out.

On 11-Apr-1998 W7GJ wrote:
I realize it has nothing to due with LONG delayed echoes, but I have heard SHORT delayed echoes several times on 2m EME as the moon passed through a section of sky.    These appear to be reflections from large relatively geostationary satellites, and aboviously vary depending on the orientation of the solar panels, size of the satellite, etc.  I would think these would be even more apparent on the higher frequencies, where the antennas are generally sharper and higher gain.

The propagation I observed was more of a "backscatter" phenomenon, since stations on the earth would both have to be reasonably close to each other to notice this by accident as the moon appears to pass through the same apparent place of sky behind an orbiting object.  However, if stations we actually INTENDING to utilize this type of propagation, I would think that quite distant contacts could be made.  To my knowledge, however, stations have not INTENTIONALLY capitalized on the vast amount of reflective junk orbiting the earth.

The main reason I mention this phenomenon at this time, is to remind stations hearing extraneous echoes that it is very important to carefully time all the echoes (and record them, too, if possible).  Not all non-moon echoes are LDE's.  I often wonder how many times we hear such things on VHF bands and attribute the propagation to some "natural" phenomenon such as meteors, Es,

On 11-Apr-1998 W5UN wrote:
I have been hearing and reading about long delayed echoes from time to time, by various hams, in various circumstances, over the years. The longest delayed echo I've ever been able to measure has been about 2.8 seconds (and it was my own).

After 46 years of intensive CW activity on the Ham Bands, including the last 18 years on 2 meter eme, put me in the "Oh Ye Of Little Faith" category (read SKEPTIC).

On 11-Apr-1998 GM4JJJ wrote:
Please note the format of the files in ARRL CDROM is not .pdf but .tif (Black and White single bit TIF) They are scanned images of the pages in these old pre-DTP QSTs.

On 11-Apr-1998 K3PGP wrote:
Thanks to the help from people on this reflector I was able to locate most of the material that I was looking for.  The only thing I have NOT located is the original audio cassette.  I'll continue to look.  If I find it I'll upload the audio file.

For those of you that don't have access to the original material I have posted all that I have located so far on my web site (http://www.qsl.net/k3pgp) in the Notebook section.

I was also a skeptic of LDEs (especially on an EME circuit!) until it happened to me.   In over 40+ years of operating on all bands from VLF through laser it only happened to me during a vary narrow time slot between 1976 and 1978.  I never heard anything like this before or after those years.  During that time frame other EME operators reported hearing similar signals but like I said, until it happened to me I simply wrote it off to other explanations such as QRM from other stations, etc...

I present the original data on my web site for further analysis.  Perhaps in the past twenty years there maybe some new ideas on what was going on. So far the plasma cloud seems to be the most logical explanation...

On 11-Apr-1998 GM4JJJ wrote:
I think that the tape would have so much' print through' by now that there would be multiple echoes on it by now John!

On 11-Apr-1998 GM4JJJ wrote:
A search through 1950 - 1979 QST CDROMs with my own MacQST Database found the following references to Long Delay Echoes.

Please don't as me for copies of these! - they are Copyright ARRL.

Title,Column,Last Name,FirstName,Callsign,Year,Month

"More on Echoes","Correspondence","Trombly","Larry","W0DCB","1952","12"
"Radio Echoes","Correspondence","Dyner","Benjamin","W3KBD","1953","1"
"Radio Echoes","Correspondence","Hartley","Margaret","W6JPI","1953","1"
"""long delayed echo"" phnomenon","Strays","Holcomb","Maj Bill","W9SDP","1956","7"
"Long-Delay Echoes","Technical Correspondence","Josephson","Louis A.","K4APE","1957","7"
"Mammoth Echo Chamber","Correspondence","Wiggins","Brown","W6ONY","1962","3"
"Long-Delayed Echoes...Radio's ""Flying Saucer""Effect","","Graf","C.R.","W5LFM","1969","5"
"Long-Delayed Echoes...Radio's ""Flying Saucer""Effect","","Lomasney","J.M.","WA6NIL","1969","5"
"Long-Delayed Echoes...Radio's ""Flying Saucer"" Effect","","Villard,Jr.","O.G.","W6QYT","1969","5"
"Long-Delayed Echoes...Radio's ""Flying Saucer"" Effect (May 1969 QST)","Feedback","","","","1969","6"
"""Echo"" Transmitting Facilities","Technical Correspondence","Tamchin","Arnold","W2HCW","1969","10"
"Echo Signals Analyzed","Technical Correspondence","Gold","Nathan","K1MIA","1969","10"
"Morse Radio Signal Echoes","Technical Correspondence","Frazier","Larry M.","WA3LHG","1969","10"
"Radio Signal Echoes","Technical Correspondence","Geiger","John M.","WA0TVZ","1969","10"
"Long-Delayed Echo AR, A","","Graf","C.R.","W5LFM","1970","2"
"Long-Delayed Echo AR, A","","Lomasney","J.M.","WA6NIL","1970","2"
"Long-Delayed Echo AR, A","","Villard, Jr.","O.G.","W6QYT","1970","2"
"Long Delay Echoes","Correspondence","Graf","Calvin","W5LFM","1973","2"
"Ghost Echoes on 1296 MHz","Technical Correspondence","Rasmussen","Hans","OZ9CR","1976","6"
"Long-Delayed Echoes on EME Circuit","Technical Correspondence","Lorenzen","Howard","W3BLC","1976","6"
"More Ghost Echoes","Technical Correspondence","Goodacre","Alan","VE2AEJ","1976","6"
"Ghost Echoes, Phase 2","Technical Correspondence","Garibaldi","Antone","W6NWO","1976","9"
"Two-Meter Echoes--Or Magnetic-Tape Print-Through?","Technical Correspondence","Eickerman","Curtis","WB6PUS/7","1976","9"
"Ghost Echoes Again...Echoes Again","Technical Correspondence","Fletcher","Don","K4KCK","1977","3"
"Long-Delayed Echo Revisited, A","","Cohen","Nathaniel","N1IR","1978","2"
"Long-Delayed Echo Revisited, A","","Davis","Franklin","WA1TCK","1978","2"
"Long-Delayed Echo Revisited, A","","Davis","Jonathan","WA1TCL","1978","2"
"Echoes: An Amateur Observation and a Professional Reply","Technical Correspondence","Frank","Victor","K6FV","1978","5"
"Echoes: An Amateur Observation and a Professional Reply","Technical Correspondence","Lomansney","James","WA6NIL","1978","5"
"Echoes: An Amateur Observation and a Professional Reply","Technical Correspondence","Villard, Jr","Oswald","W6QYT","1978","5"
"Echoes: An Amateur Observation and a Professional Reply","Technical Correspondence","Yurek","John","K3PGP","1978","5"
"LDE Hoax","Correspondence","Villard, Jr.","O.G.","W6QYT","1970","5"
"LDE Hoax","Correspondence","Hubbell","Eugene","W7DI","1970","5"
"LDEs, Hoaxes, and the Cosmic Repeater Hypothesis","","Cassam","R.P.","","1971","5"
"LDEs, Hoaxes, and the Cosmic Repeater Hypothesis","","Fraser-Smith","A.C.","","1971","5"
"LDEs, Hoaxes, and the Cosmic Repeater Hypothesis","","Villard, Jr.","O.G.","","1971","5"
"Two Possible Explanations for LDEs","","Clark","C.R.","WB4OBZ","1971","11"
"More Reflections on LDEs","","Simpson","Richard","W6JTH","1978","2"
"Out-of-this-World Explanation of LDEs","Technical Correspondence","Burke","Forrest","K4SK","1978","2"
"Solar Wind a Cause of LDEs?","Technical Correspondence","Wolking","Henry","W4BNF","1978","10"

On 12-Apr-1998 G8MBI wrote:
lance wrote:-

>I realize it has nothing to due with LONG delayed echoes, but I have heard
>SHORT delayed echoes several times on 2m EME as the moon passed through a
>section of sky.    These appear to be reflections from large relatively
>geostationary satellites, and aboviously vary depending on the orientation of
>the solar panels, size of the satellite, etc.  I would think these would be
>even more apparent on the higher frequencies, where the antennas are
>generally sharper and higher gain.

yep, thats why I threw the comment on the table as well Lance...I think this is much more common..

I had/have always been told that satellites represented a too small reflection area to have this happen...BUT I also remember the experiments (and apparent partial success) many years ago between Chris G4DGU and SMxxxx (sri forgot call)

with 4 (5?) ASTRA satellites now in the same spot in the sky in europe to supply direct broadcast Tv and several others within the same beamwidth of many stations as well..is there enough volume of material now available..??..anyone tried..??...any mathmeticians tried a budget calc..??

this might not (would not) get found by accident as the moon rarely , perhaps even never, passes behind this spot except maybe at very low dec. dare you to try for echoes.....sm5frh, f3vs, i2fak for example..

how is DBS progressing in the US...do you yet have tight groupings like this..?? maybe Dave UN and a few others might give it a go also...

CARE needed...I frequently hear what appear to be these short reflections and have often then found a europe based station on the same frequency on the same tx period ...ie a second station that was not immediately heard via eme generating real MS reflections..

On 12-Apr-1998 K3PGP wrote:
After going through some old correspondence concerning my LDE experience I think I finally figured out how one station might experience an LDE when the station he is working hears only normal EME signals.

The info is at: http://www.qsl.net/k3pgp/Notebook/Lde/ldepath.htm

If there is something wrong with the above path (type) just go to the web site and follow the links from the Notebook section.

It is based on the plasma cloud theory which  has been observed by some of the commercial radio telescope and interplanetary radar setups...  Of course it's only one of perhaps many explanations.  I'm hoping someone can offer some other views on this subject and perhaps other theories.

PS - I appreciate the offer of people trying to send me copies of my original article in QST.  However, as I have located most of my original material plus the issue of QST where the article appeared I do NOT need this.  That info is now on my web for those of you that don't have the original article.  Thanks !!!

I am still going through my collection of old tapes.  I have located a collection of stuff from 1978 through 1982 that exists in three different formats.  Cheap audio cassettes, VHS Hi-Fi 17 Khz spectrum recordings, and experimental digital audio on CPM 8080 S-100 disks which I can no longer load unless I put one of the old S-100 systems back together!

The spectral recordings are similar to what Leif is doing.  I took the IF of the Rx, ran it through a 17 Khz wide 10.7 Khz filter, then into a product detector.  The resulting 0 to 17 Khz spectrum went into one of the Hi-Fi inputs of a VHS tape machine.   On the other channel is the 'normal' audio of what the Rx was tuned to at the time.   Back then I used to play these tapes back into the Rx using a VLF converter tuning from 0 to 17 Khz.  The actual useable bandwidth ran up to 95 Khz as this machine
did NOT have low pass filters on the inputs like current machines do!

This is still a very cheap way to do spectral recording and that is why I mention it here.   VHS Hi-Fi machines are very common today (around $150) and have the advantage that you can put 6 hours on a $2.00 cassette! (The Hi-Fi audio response is unaffected by tape speed as it is recorded on 1.4 and 1.7 MHz FM carriers with the rotating heads.)  My machine was modified so I can record separate audio on the linear audio track giving me two 20 Khz audio channels plus a low bandwidth audio channel suitable for 'normal' audio.   The original tapes  appear to play back just fine on current machines even though they are approx. 20 years old.  However, those tapes that were recorded using frequencies above 17 Khz show very reduced (but useable!) output above approx. 15 Khz when played back on modern equipment (due to the low pass filters).  I suppose one could jumper these out for wider bandwidth spectral recording.

I ran across some rather interesting recordings of the WA6LET tests and some early Oscar translator stuff.  The WA6LET tape was done just before and during moon set on the east coast.  The tape is quite an earful even when listening to it broadband by ear as everyone on the east coast was calling WA6LET at the same time as the moon set.   There is no problem hearing WA6LET directly off the tape although the 'beat' note is a LOT higher than what one is used to listening to!

I'm going to see what I can do to get some of this stuff into digital audio files...   Hopefully the LDE tape is in this collection somewhere.....

On 12-Apr-1998 PE1ECM wrote:
On his webpage John mentioned possible relationship between (lunar) lde's and solar flares, aurorae, radio blackouts etc.

I would emphasize that in this enumeration different causes of disturbances are involved. This distinction could possibly help a bit understanding plasma cloud theories on lde.

So, does information exist on relationships between lde's and, on the one hand, ionospheric disturbances  by x-rays, extreme uv, gammarays, protonflares and, on the other hand,  interplanetary/geomagnetic field disturbances  by coronal mass ejections and coronal hole disturbances on the other ?

On 13-Apr-1998 JA9BOH wrote:
I had been a skeptic of LDEs like others .On 11th  JH7SIA and JA7AGL who are active on 144 EME  visited my shack. Talking on the bad condx in the Dubus /Ref contest , JH7SIA told me about his strange experiences on april 5th moonset .
Though he did not remember it correctly , he received strong LDE s . He also received echoes of F3VS  skewed direction from the moon . Was there another reflecting objects in the sky . There might happen  unusual propagations on 144MHz on april 5th .

On 13-Apr-1998 K3PGP wrote:
I received the following Email over the weekend and it jogged my memory about some VLF recordings I have of LDEs.

On Sun, 12 Apr 1998 11:25:23 -0700 (PDT) dbcntcas@teleport.com (Dave
Bernhardt) writes:
>John: I have not been following the LDE thread that closely,
>but thought I would inject my 2-cents worth.
>I have personally seen LDE on 6M in the earlier 70's.
>On ELF (RF at audio frequencies) one can hear at times LDE from
>natural sources.  These sound like whistles!  I forget the address, but
>can download .WAV recordings of these sounds.  The way this happens is
>RF generated by lightning is ducted thru the magnetosphere (which
>WAY out there.)  Thus, I can conceive that some of our RF could also be
>ducted in a similar fashion.
>        CUL de Dave, N7DB (CN85)
>Dave Bernhardt                   Internet: dbcntcas@teleport.com
>Boring, OR

I recorded a whistler / LDE event several years ago.   If you've never heard a whistler or an LDE, here are examples of radio signals generated by mother nature.   These signals are NOT man made.  What is so unusual about it is you can hear the main event then a ghostly echo a few seconds later.

When I first heard this I wasn't sure if I actually heard the the echo or not as I never heard anything like this before.  (Never heard one since, either!)  I don't know if this has any relation to LDEs on an EME circuit as we may be dealing with more than one cause and effect here but it's worth a listen.  If LDEs occur in nature then I see no reason why they can't occur on man made signals.

It's at: http://www.qsl.net/k3pgp/Notebook/Vlf/vlf.htm

The file is approx. 80 k.  As usual, if I managed to mistype the above, just go to the web site and check in the Notebook section under VLF.

This recording was done by connecting my 80 meter dipole to the input of an audio amp.   Nothing special in the way of hardware or antennas !!!  I used an audio transformer to isolate the input otherwise the hum was extremely high.

PS - I also just received Email mentioning LDEs on 40 meters that occurred just recently.   I'll see if I can reproduce them here.  Normally this would have nothing to do with EME, but I'm open to ALL possibilities.  I've been watching the sun over the past couple of months and there are some HUGE spots visible.  At least one was visible to the naked eye at sunset.  There have also been some HF blackouts and aurora.

On 13-Apr-1998 KV6J wrote:
     The reference material on LDE makes fascinating reading.  Since I'm new on www I didn't realise how difficult it was to keep track of 'where you've been'.  During the last week I read a reference to Arecibo's (and perhaps others') reception of E M E M E or double echo.  Can anyone help me find that (or another) reference on this subject.

On 14-Apr-1998 CT1DMK wrote:
My 2 cents... (my... 2 long... long....cents)

Some years ago I discovered some reports of the LDE fenomena along with the most common attempts of explanation. I have no personal observation, at least a defenitive and conclusive one (only some abnormal echoes on 2m some time ago... but too short time to be sure of anything).

Just by accident, while trying to find something else, I found on a plasma phisics book, a very intersting plasma phenomena. But before ... Let me make just a few commets about two of the comon heard explanations:

-The EMEME path is on the 300dB's range... !!!!!  I Dont take this one... (at arcibo reports state that  the second echo was week...)
- The plasma cloud behind the moon at greater distance... doesnt fit the elementar plasma phisics at all. (If an LDE was present on 1296MHz for 10 seconds, 2m  QSO's from US to VK would be done for hours with hand-helds hi.)

Could our IONOSFERE be the source of the LDE ?!

<< I will try to write as simple as I can... so I will commit some inaccuracies... Phisic folks... please forgive-me >>

An electromagnetic wave can interact with a plasma and create an "plasma wave" by exciting the plasma particles with their energy. If the electrons are excited we may end with one of several modes of propagation of an electromagnetic wave. But if the heavier particles are excited, the ions, we will get a ion wave that can be an acoustic wave ("mechanical movment") beeing electrostatic nature (i.e. cyclotron movement)  or electromagnetic nature (such as Alfven waves and Magnetosonic waves).
The Ion waves are orders of magnitude slower than electromagnetics waves, since the ions are heavy.

This kind of waves (depending on the exact type) will decay along its propagation (as we would expect...) But there are a kind of decay, the "Landau damping" wich does not involve any dissipation of energy could therefore be a reversible process if the same conditions appear in the reverse order. ( see what I mean ? hi !!!)

Consider a plasma wave is exited w/  frequency F1 and at the same plasma stream another plasma wave is excited w/ frequency F2. At some distance from this points, so a few time after, if a frontear condition is imposed to the plasma wave an electromagnetic wave with a frequency (F1-F2) (yes... as a mixer) will be radiated. If at this second place the F2 signal was still strong and exciting a plasma wave we may well recover (F1-F2)+F2  that is F1 itself. This wave may just  travled a few Kilometers and be delayed by 2 or 3 seconds. However there are some restrictions on the frequencies and their relation. (they both must excite the plasma and etc...) Depending how the wave propagates and what energy the wave may gain, this process can even present amplification.

This fenomena was studied and demostrated in laboratorial experiments, and repeated and as mayny times as wanted...

This is called "Plasma Echo" and the Theory behind is "Parametric instabilities".

Did you realize that I just described a natural parametric amplifier (or parametric converter) ?

Do you think this is behind some of the ghost receptions of short wave and low-VHF misplaced broadcasts, and or short strange VHF bursts, non meteor-scatter related ?!

For an EME LDE to occour we would need a matching frequency for the pumping (parametric amplifier terminology) well foe 2m we may need something on 432MHz... or  1296MHz so... (harmonic relation was widely used in parametric aplification).

Could be that an LDE is rare not only because of the correct plasma interactions to occour but also the need of a matched pumping frequency, Key Down during the LDE event ?!

No LDE's up to date have contrary evidence to the above theory, but neither forward...

I dont know if I buy this one also... I will be among the ones waiting for more...

Please make your comments...
(If you dont, I will presume you didnt reach this point hi...)

On 14-Apr-1998 W8MQW wrote:
  Was talking with Steve K1FO last night on 3865. He and Frank (NC1I) have both heard long delayed echos on 432, but only 4-5 times in 20+ years.

On 15-Apr-1998 CT1DMK wrote:
Thing are getting worst and worst to be found here hi...(LDF ?!   L. D. finding hi hi hi)

For those interested...The references for the "plasma echos" and "parametric instabilities" are:

Book refering the articles.

Original articles:

I never succeded to get the original experiment articles. If you find them... I would appreciate a copy.

On 26-Feb-1999 DK9ZY wrote:
I had a nice random QSO yesterday night with UA4API.
I received him twice."Both" signals were peaking 319,strong QSB, and had similar tone hight.
The second signal appeared at the same time with an additional delay of approx. 2-3 sec.

I have observed similar occurence some years ago on signals from SM4IVE and VE7BQH.Both are (were) big guns.

Any explanation on that kind of Long Delayed Echoes ?

On 26-Feb-1999 GM4JJJ wrote:

I wonder? - Do you have a tape recording of any of this for analysis?

I have to say I am sceptical. Chances are that what you were hearing was another station on same frequency calling. In the QSB it is sometimes difficult to tell that it isn't another station.

On 26-Feb-1999 DK9ZY wrote:

It was easy to verify that both signals belonged to UA4API,because he uses obviously a nonelectronic keyer,pretty slow speed and some frequency "chirp".
At one end of his sequence i heard both times his call, time-delayed.Very similar to double receiving of a tropo and eme signal. It was interesting to hear that both signals had different QSB,but similar fieldstrength.From time to time you could hear one of the two signals and some times both at the same time.

I could not record the signal(s).

On 26-Feb-1999 GM4JJJ wrote:
Hi Wolf,
         Interesting! - Pity no recording of it though. Why dont you all leave a tape recorder running when on EME? - It would be real nice to hear some of these signals.

We don't know if what you were hearing was a LONG delayed echo or a direct signal (somehow) followed by the EME delayed echo.

On 26-Feb-1999 W7GJ wrote:
Certainly something to consider is that there was a signal being reflected off something relatively close (meteor, satellite, airplane, etc.) which was being heard first, then followed by the EME signal.  I heard this phenomenon 15 or 20 years ago on VE7BQH, and the dual echoes persisted for several transmitting sequences (until the moon moved from the same spot in the sky as the object causing the faster echo). 

On 27-Feb-1999 N7WS wrote:
I experienced something similar when working W5UN many years ago.

The moon was very nearly set for him (looking west) and not a great deal above the horizon for me (in Arizona).

I was copying him fairly well, when I heard what I thought was another station, slightly off frequency.  It was confusing at first, before I realized that I was hearing Dave both off the moon and via what I believe to be tropo backscatter.  There was a lot of doppler and of course the difference in time delay.

I don't know whether this is possible on the path you were working, but it makes sense to me for our path.

On 27-Feb-1999 K3PGP wrote:
Very important information:

Did both signals have the same audio frequency or was one lower or higher than the other?   If they were different which signal was higher pitched and were you listening in the USB or LSB position???  If the two signals were of slightly different pitch can you estimate what the frequency difference was?
Was the moon rising or setting at your QTH at the time of the event.  If you can provide the time and date I can punch it into a tracking program.

This information is very helpful in determining the origination of the other signal.   As others have suggested a tape recording would be extremely helpful but it's too late for that!

To read about a well documented (but very old!) LDE on EME see my web site in the Notebook section.  This one was heard on and off for about a month and by more than one station.  Unfortunately there weren't as many EME stations on the air back then.

John - K3PGP

PS - How far apart are you two geographically and in what direction is the other station from you?  I know I could look this up but you can save me the trouble!

On 28-Feb-1999 DJ5RE wrote:
Hallo to all,
here another comment to the phenomenon with UA4API. I had sked with him some weeks ago, and he was moving in QRG very quick. I followed his signal for about 1 kHz of drift, about 200Hz /period. Suddenly he was back where I got him the first time, but starting drift up again...Sometimes he made really jumps, it was a really hard QSO although signal was good....May be another reason.....

This is the contribution I got from W4BZZ on 18-May-2004. Thanks John!
Although it has been more than a decade since I was an active ham (still licensed, however, as W4BZZ with intentions of returning to the air in the next year or so), I have long remembered my own encounters with the LDE phenomenon in the HF bands (primarily 15 meters). When I happened upon your Web Site earlier today, it occurred to me to wonder if an old idea initiated at Oak Ridge National Laboratory by my colleagues and me might have been offered as a possible explanation for the LDE effect. A quick perusal of on-line resources suggests that something very similar has indeed been suggested (CT1DMK).

Our idea is somewhat simpler, in that it does not require the presence of two RF signals at the plasma cloud or, better, duct. In brief, it is at least conceivable that, at the lateral boundary of an ionispheric plasma duct, there is sufficient non-linearity to lead to conversion of an incident RF signal into a longitudinal plasma wave that would propagate through the duct as a magnetoacoustic wave. At the opposite side of the duct, the same non-linearity may be sufficient to transform a portion of the magnetoacoustic wave back into a rough facsimile of the original RF signal. The conversion process, of course, would be highly non-linear and one would expect any modulation of the incident RF signal to be extremely distorted in the "reconstituted" signal.

This is at least not inconsistent with those reception reports with which I am familiar (by no means all of them!) and with my own experience. When my colleagues and I were toying with this idea (25 or so years ago now), we made rough calculations of the expected delay for ducts of plausible dimensions. If memory serves, the calculated mean value was in the neighborhood of 20 seconds.

If it were to be concluded that the mechanism we propose is even approximately correct, it should be possible to undertake a concerted, amateur-led effort to verify it. If LDEs are the result of natural processes in or near the earth's ionosphere (the notion of "alien probes" I shall leave to others!), it is not unreasonable to suppose that the instances that have been observed are only the strongest of what may be a generally occurring, but usually much weaker, phenomenon. A planet-wide, GPS synchronized system of receivers tuned to cover a (large) predetermined set of terrestrial "beacons" would provide, via the Internet, a continuous stream of data to a collection of desktop computers (in the general manner of SETI@Home). The goal would be to analyze the data (after suitable preprocessing and selection for optimum path intersections) over a broad range of time delays. Suitable algorithms, algorithms easily within the capabilities of modern desktop computers, already exist by which the LDE signature could be extracted from these data if the effect is real.

Should there be sufficient interest in the development of an LDE detection project, I would be happy to participate.

This is the contribution I got from James Rosa on 8-September-2004. Thanks!
I am a licensed commercial radio operator, previously a first class over 20 years, then grandfathered into the newer general radio operator license. I was never able to get my "ham" ticket due to an inability to decifer morse code.

The obvservance of the above phenomenon was discussed on the Art Bell radio show over KFI-AM. I had an opportunity to actually hear voice copy resulting from this phenomenon. Art claimed a 24 second delay, occuring at a frequency of about 38 mhz, Interestingly enough noize rejection was about relative to a 4db s/n. Given a test signal to compare with a level of about -137dbv could provide such a voice response. I am referencing to signal into the RX.

Going by the delay, some 4.4 million miles of effective path would have to be involved. The usual relationship of q/dsq would result in about -440dbv getting back home. This is fairly hard to detect, even for big radiotelescopes.

On the other hand, I have had several personal experiences with some fairly disruptive RF anomolies called ducted path phenomenon. One such occurance at about 163 mhz, nbfm mode, 1 watt TX, whip antenna, portable, hand held caused direct rf level interferrence about 130 miles away, cross open dessert terratory, cross a mountain range and onto an urban area. This condition occurred one day in 1964, and lasted about 3 months, then quit as suddnly as it started. The effect was one of signal ampification with a phase shift acting on the side bands, as if the modulation index was shifted at the TX end. The RX's at both ends were commercial communications grade nbfm, actualy nbpm, operating at about -128 dbv for -20dbq. The units at this urban area were desensitized to about -116.5dbv for 10db s/n, making most of the fleet unusable when the distant QSO was in progress. As it was, I Was in charge of the comm. at the distant site, and had similar business at the interupted site.

This was an encounter with a ducted path. The phenomenon appears to act like a geo specific magnetic/ionic waveguide with a one way direction, similar to a directional coupler. Allowing for natural parametric amplification within a floating shape waveguide, potentialy a wide range of frequencies could be accomodated. The idea of unidirectional would follow , since the exciting enregy field is from the TX toward the RX at the other end. These things don't seem to operate the other way when the TX is operated from that other end. This brings us to the relavent question of the LDE phenomenon. 

Allow for a geospecific DP to form between point "A" and point "B", where point "B" is the geospecific area of point "A". At the time of rf energy entering the DP at "A" / "B" the entry point is selected from that choice. This configures the path and the key down segment is "plasmicly contained" and electromagnetically transported through a negative impedance path withought loss in that unidirectional DP. When the DP was formed it was a loop, unlike others which were arc like. This formation has path loss due to less than perfect magnetic/ionic system provision, as well as the co field intermodulation occuring when the bend in the path comes to a net 360 degrees. For the LDE of Art Bell a net path throughput of about -183 dbv would have to have been experienced. Supposing a TX of 1 Kwpep, about 47 dbv. A DP gain of about 277 dbv above q/d squared path loss of 440 dbv would be required to output the -183 dbv. The effective length of path would remain about 4.4 million miles; however, it's geospecific shape would probably be along the lines of a vortex compressed into a much smaller physical space.

These are the contributions I got from D.B. Muldrew. Thanks!

(DISCLAIMER: The two above articles have been placed for downloading here with the express permission of D.B. Muldrew.)

This is the contribution I got from Sverre, LA3ZA

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2 user comments

#2 - G8SHE - 11/17/2011 - 21:44
A very prosaic explanation, which would make it more difficult to recognise true LDEs (at least the VHF/UHF ones) would require some answers from NASA and the other agencies which put up satellites in the days before brick-wall digital filters. Namely:
1) Which satellites have used linear store-and-forward systems?
2) Are they, even occasionally, alive? (think of the longevity of some amateur birds...)
3) Did they have passbands close to amateur bands?
4) What were the shape factors of the filters?
5) What was the store-and-forward delay?
6) (Ideally) What are the Keps?

With this information, it should be possible to see if any L-band store-and-forward satellites with, say, only 60 dB of rejection of 1296.01, could be storing and forwarding messages, especially if they were designed for low-level inputs.

Even if the Keps are not forthcoming, some intelligent guesswork, working back from current keps as monitored by CelesTrak should enable correlation with known events as recorded in this reflector.

Unfortunately I'm not at all clever enough to do either this or the final bit of analysis/detective work: correlating these guessed keps with the observed Doppler shifts, especially when every calculation would have to be done twice, one allowing for EME (nence lunar doppler) plus store-and-forward and one for store-and-forward only. If the doppler works out close to an observed doppler, this would indicate a "man-made" LDE.

Terestial store-and-forward systems could be relatively easily eliminated because there wouldn't be any doppler, but any frequency discrepancy between receive and transmit could give a false doppler reading - a 300 Hz Rx/Tx error could be mistaken for a 300 Hz doppler; only with a measurement duration of at least hundreds of milliseconds, could the two effects be separated. Also, a hightly elliptical satellite has very little doppler at apogee. This could cause a true, i.e., natural, LDE to be ruled out incorrectly. Perhaps someone cleverer than me can suggest a way to eliminate these false results.

I hope someone is able to tell me that there is a flaw in my reasoning, as I'd much rather believe that there is new science in LDEs, not just old space-junk!

Store and forward would have been a very useful technology in Cold War days - which is why I suspect that some agencies might be reluctant to give details of (albeit obsolete) technology which may have been, and perhaps still is, used for communicating with agents overseas. Without their co-operation, the problem of recognising what is a real LDE will be that much more difficult.

#1 - Olaf - 09/16/2011 - 07:07
Sadly, this subject appears to have ceased to interest people some time ago. It is still of great relevance to a new theory which would also find experimental evidence relating to LDEs. For this purpose I need some data re longer delays and including location and EXACT times of the phenomenon as this would relate to the likely cause. Would appreciate any emails with data re this or ideas where I could find such exact data.

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