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Long Delay Echo's

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Dave Robinson
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Hi Guys

Does anyone know of any serious study of the Long Delay Echo phenomena? I know about the original study undertaken in Norway just before the 1930's which Duncan Lunan was able to generate some very interesting results based on the interpretation of the echo's coming from a Bracewell Probe, and by fiddling the results slightly came to an interesting conclusion regarding it being a probe from the constellation of Bootes. I also know he later withdrew this conclusion. I have read about some amateur Radio guys in the late 1970's being able to demonstrate the effects, however from what I have read, their experimental technique was somewhat suspect (hope I am not doing them an injustice here) with some of the echos being interpreted as transmissions from other users being interpreted as echos.

I must admit some of the explanations of the effect always appeared to be a little contrived to me, and I wondered if anyone had recently had a go at repeating the experiments using modern DSP techniques; I had in mind transmitting true pseudo random sequences, and using autocorrelation to measure any echo, also accurately checking for Doppler effects etc. to truly characterize the return echo.

I am not actually suggesting that there is a Bracewell Probe in the Solar System, nor that the LDE echo phenomena is associated with such an entity, But I would hazard a guess that if there is such a probe, then it would echo a signal which ever frequency we used, and with a member of the quest having his own radio telescope and access to a DSP package like Baudline, it might be an interesting experiment in active SETI. I assume that the ATA is to busy to try.

Regards

Dave Robinson

sigblips
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The Long Delayed Echo

The Long Delayed Echo phenomena and Bracewell probes were both new to me so I did a little research.  Here are some links that others may find useful:

This is all fascinating stuff and very sci-fi. I particularly liked the numerous looping and reflecting explanations for the LDE phenomena.  The closest experiment that setiQuest has done is the L4 data collection and my analysis. Still many unanswered questions almost two years later.

I'll mention your suggestion to eb3frn when I see him on IRC. A potential problem is that the Bracewell probe experiment requires transmission capability.  The ATA and most amateur SETI researchers can't transmit. The next version of baudline I'm working on can currently do 16M point autocorrelation which would be very useful for this experiment. That's a limitation of my low-end development hardware (2009 Mac mini with 4 GB RAM). I'm investigating gigapoint+ FFTs for a future version.  Fun stuff ...

Dave Robinson
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Random thoughts on the LDE phenomena

I have been giving the LDE phenomena some thought and have come to what I think may be interesting conclusions.
 
If we assume that the phenomena is actually real, i.e. Long Delayed Echo's actually exist, and I think that the odds are that it does, we have at least 2 questions to answer

  1. Is the effect a purely natural one, e.g. plasma clouds at a Lagrange point (I guess the most probable option
  2. Is it artificial, e.g. the Bracewell Probe either at a Lagrange point, else in Solar Orbit (I guess a very low probability option)
     

I have been wondering if it would be possible to differentiate between these alternatives, and came to the conclusion that it might well be.
 
Let us firstly consider the Probe hypothesis; presumably it has been placed there by an alien race, perhaps many hundreds, maybe thousands of years ago. The chances of it having arrived recently is pretty small. In which case its echo signature must be broadband; the alien species doesn't know what communication band we will use, when (if) we eventually invent radio. So it must be capable of producing echo's on all of the possible wavelengths we eventually use. This, I believe may well contrast with a plasma reflector, which I would guess would have a well defined frequency distribution. I would also guess that there exists the mathematics to calculate how such a Plasma reflector, especially one containing loops would behave to different transmission frequencies.
 
A second thought is that a Bracewell Probe would need some form of threshold. It needs to be able to identify one of our signals from the background noise. It would be a complete waste of energy simply echoing the cosmic background radiation, for example. Therefore what we should see is that the echo response would not occur for very low amplitude signals, but would switch in after the signal strength reached its attention threshold. Whereas (sounds of guessing wildly!!) a Plasma reflector would probably reflect a signal of any strength. This suggests two experiments, one is that we could use a very low power (i.e. cheap) transmitter, and broadcast a known pseudo random sequence, whose length was relatively long, but shorter than the expected minimum echo period, so that the telescope could be switched from transmission to reception. I am thinking here of about 1 second burst. Using a matched filter during the reception phase would allow an echo to be identified even if it was way way below the ambient receiver noise. I would expect to be able to detect a Plasma reflection, but not a Bracewell Probe reflection. An alternative to this may well be possible, and that is undertake a correlation between a portion of background noise taken now, and one could expect that the Plasma cloud would have also received this sequence and echoed it, thus if there is any trace of an echo, then the effect is probably caused by a natural process. This is a DSP exercise that I guess Baudline could easily undertake on the Lagrange data set (or any other I guess) especially with the longer processing capabilities that Sigblips is now building in.
 
Any thoughts?
 
Regards
 
Dave Robinson

sigblips
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My thoughts: * The L4 and L5

My thoughts:

* The L4 and L5 points are about 93 million miles away (picture). So round-trip for the speed of light is about 16 minutes.  This seems far longer than the LDE phenomena duration.

* Let's ignore the multiple loops around the Earth explanation.  Expanding on my thought above. If we know the LDE delay duration and the speed of light  then we can draw a circle around the Earth of where the reflector is located. That would narrow it down.

* We could do the L4/L5 baudline-correlation experiment you mentioned but unfortunately the setiQuest L# datasets are too short in duration for a full round trip even if we correlated the head of the data with the tail. 

* Your LDE experiment sounds a lot like the planetary radar Arecibo engages in. By definition, a Bracewell probe should reflect a radar signal at an amplitude stronger than it was received.

Dave Robinson
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Earth - Moon system also has Lagrange points

You are certainly right about the Earth - Sun Lagrange points, the echos from them don't tally with the LDE results that I have seen, from memory they appear to be of the range 3 secs to several minutes, which certainly is a much too short timescale for a round trip to the L4 and L5 Earth - Sun points. However they are much more intune with a 'reflector' of which ever sort in one of the Earth - Moon Lagrange Points, perhaps a more logical place to place a Bracewell Probe, if you wanted to 'keep your eye' on planet Earth (you could of course bury it in the Tycho Crater on the moon;-).

Yes to a certain extent there is a similarity to what I am suggesting and the Arecibo planetary radar, except what I am suggesting is using a transmitter of a few watts, or less, not Kilowatts, something that should be within the affordability of an amateur radio enthusiast.

Of course there is the real major problem in trying my experiment, and that is government red tape, don't know if it is still a requirement of getting a tranmission licence - you used to have to learn Morse Code.

Regards

Dave Robinson

sigblips
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Here in the States the Morse

Here in the States the Morse Code requirement for a Ham license was removed several years ago. The problem is that Hams are only allowed to transmit on a handful of frequencies. What if a Bracewell Probe is programmed to only respond at one particular frequency? A Bracewell Probe experiment really requires a full scan of all frequencies from DC to daylight. As you say, the government red tape for this sort of experiment is going to be a real problem.