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Old 04-06-2014, 03:57 PM   #201
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As Nords pointed out, many critters make all sorts of sounds in the ocean, some audible to humans others beyond our range of hearing.

My experience from long ago when aboard an Oceanographic resaerch ship, is cacaphony of sounds all over the spectrum. Some are known which species the noise originates from some not. We used to drag along hydrophone (underwater microphone) strings which were nearly a mile long for specific sonar listening purpose. They were very wide band, could identify a few hertz, to well beyond 50 Khz. The recorders were tuned and and filtered for specific frequencies.

At times we deployed sonobuoys, which are floating radio transmitters, with hydrophones dangling deep down. The range of sounds were somewhat different from the towed array. Especially if dangling below the thermocline.

We had the capability to route the hydrophone output to an amp and loudspeaker. At times we would turn it on just for amusement. Therange of sounds varied from regions ie. North Atlantic, Pacific, Indian Ocean or off Antarctica. The variety also changed by the time of day, so much that without looking out one could tell roughly morning, mid day, evening, late evening or midnight.

Our precision depth recorde also would show trends of mini critters migrating to near the surface in the evening and disappear in the morning.

Anotherwords what they thought they heard could have been anything. Many of the critters communicate by very short squeaks, whales tend to have long moans among other sounds. They can be heard for hundreds of miles.

As the old Ginzu knife commercals used to say, and there is more, a lot more.
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Old 04-07-2014, 12:23 AM   #202
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More sounds were heard, consistent with black box pings (1 second apart, for extended periods - 2 hours, 15 minutes). Looks like they finally found the haystack! Good job, to the crew of the Australian ship.
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Old 04-07-2014, 09:34 AM   #203
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These signals picked up by Ocean Shield seem to be more than just random underwater "noise". It appears to me that this is the first new hard evidence of the fate of MH370 since the satellite pings were announced many weeks ago. We'll see if they find anything in this location.

Interestingly enough, the map of the area where the contact was made is relatively far to the east. If the plane really did fly far enough west to avoid Indonesian airspace, it would have had to have been flying roughly SSE in order to end up where it did. I'm not sure if it means anything, but the plane could very possibly have been heading almost directly towards Perth, Australia.
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Old 04-07-2014, 09:48 AM   #204
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I'm still getting my mind over the fact that just as things looked like the whereabouts of what happened seemed lost, in the last days of battery life, suddenly pings are discovered. Lucky? Or some inside information?

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After thousands of man-hours spent searching the ocean he has a point, could a Chinese vessel just have gotten lucky and happened upon the site? The Haixun 01 picked up the first ‘ping’ at 25 south latitude and 101 east longitude, about 1,000 miles northwest of Perth, Australia, on the same frequency used by the black box recorders, 37.5Hz. They were using a hand-held device called a hydrophone. Mounted on the end of a pole it was held over the side of a very small Chinese boat.

Experts have said that discovering the wreckage with this method is not entirely impossible but is extremely unlikely.
http://www.infowars.com/do-the-chine...-flight-mh370/
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Old 04-07-2014, 10:35 AM   #205
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I bet the signal was detected by a nuclear sub but it was decided to let a surface ship *find* the signal for some reason.
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Old 04-07-2014, 10:40 AM   #206
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I bet the signal was detected by a nuclear sub but it was decided to let a surface ship *find* the signal for some reason.
My thoughts exactly.
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Old 04-07-2014, 11:01 AM   #207
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Hopefully the sub will locate the aircraft and let the surface ship claim the find.
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Old 04-07-2014, 12:36 PM   #208
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My thoughts exactly.
Ah...

MH370: missing Malaysia Airlines plane - live - Telegraph

Mentions there is a British nuclear sub in the area helping with the search. So we can pretty safely assume there are "some" America nuclear subs in the area too.

P.S. This is also apropos to reading non-US news sites...
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Old 04-07-2014, 01:13 PM   #209
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For the life of me I don't understand why someone in the cockpit is able to turn off that tracking signal.
If you're talking about the transponder, it's to avoid ID conflicts and cluttering ATC's radar with ground traffic.

The transponder gets programmed with a 4-digit number assigned by ATC when you call in for your initial clearance. You dial in the code they give you, and turn it "ON" right before you take off. A new code is assigned to you each time you start up the plane and call ATC for departure clearance.

If the transponder were simply on all the time, with no capability to turn it off, then there's a risk that the code already in your transponder (left there from your last flight hours/days/weeks ago) could happen to be assigned to another flight already in the air today. So as soon as you turn on your electronics, you'd pop up on their radar as a duplicate of another flight they're trying to guide, and they'd have no way of knowing which radar return was the ACTUAL Air Canada flight 5788 or whatever.

(Well, they do, by asking the real AC5788 to "squawk ident," which causes their radar return to blink on their radar screens temporarily, but if this confusion popped up at a critical phase of flight, say during vectoring to avoid a collision, or short final, it adds unnecessary risk to an already dangerous ordeal).
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Old 04-07-2014, 03:00 PM   #210
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Finally a local Chicago radio show got it right. They specifically said that the beacon is rated for a minimum 30 day battery life, and that the average life was reported to be 45 days.

The 45 day number makes sense to me. These things need to get certified, there are a lot of variables, and a designer would need to design in some safety margin. They would need to achieve a 30 day life even if the battery was due for replacement (that would be one of the things that determine the battery replacement cycle). Throw in a bunch of other variables, and by the time you stack them up, it would be pretty rare to have them all on the edge to provide only a few days beyond the minimum.

Wiki says there was a case where the beacon was accidentally triggered at some point, so the battery was dead before the crash.

https://en.wikipedia.org/wiki/Underwater_locator_beacon

http://rjeint.com/pdf/DK120.PDF

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FAA & CAA approved under TSO-C121, the rugged and durable construction of the DK120 insures its survival even under high-impact shock. Once activated, the DK120 will operate in water depths to 20,000 feet (6000m). Using a 6 year user-replaceable battery, the DK120 continuously sends out an acoustic signal for a minimum of 30 days.
-ERD50
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Old 04-07-2014, 03:16 PM   #211
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Perhaps when an airplane crashes in water it should start a timer on the beacon where it does not activate for 10 days. This would give ships time to get to the search area and would extend the search time to 55 days on average instead of 45 days.

It is very unlikely there will be sonar searching ships on site in the first few days after a crash, so the beacon pulse is wasted. It also is not likely there would be survivors at the bottom of the ocean.
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Old 04-07-2014, 04:17 PM   #212
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I agree. For the life of me I don't understand why someone in the cockpit is able to turn off that tracking signal.
If something is powered by electricity it can catch fire or cause electrical problems for other equipment. If something electrical can catch fire, it's not unreasonable that the crew be able to turn off the power to that device. A fire on an airplane is about the scariest and most dire situation there is--rivaled only by a fire in a sub. In both cases there's nowhere to run--you are in the can with the fire.

Let's try to keep this whole thing in perspective. Cases like this just don't happen that often.
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Old 04-07-2014, 04:41 PM   #213
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I was in the Navy and until you experience the size and scope of our oceans, especially the Indian Ocean, it is a miracle we can find anything that crashed into it. I am sceptic all about the under water pinging signals being detected. I pray that we can find the missing plane, but this should be a wake up that even though we have an NSA that can track you phone calls and satilies capable of reading a news paper print; our world is still a huge area to search. I feel so sad for all the families living in limbo, not knowing what to think?
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Old 04-07-2014, 08:13 PM   #214
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If its at the bottom of the drink at 15,000 feet undersea (and very dark down there), the next big trick will be getting to it. Then there is another bag of tricks needed if they do.
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Old 04-08-2014, 08:30 AM   #215
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In a high density traffic area, such as the terminal area or on the ground, the IFF equipment can add to the clutter on the radar and pilots have been ask to go standby on the equipment. In general just about every piece of electrical equipment can be isolated in an emergency, I.e. Fire. While I don't know but it would not surprise me that the black box's power supply could not e isolated.

My guess is that there have been far more fires on board air craft than pilots hijacking them.
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Old 04-08-2014, 11:15 AM   #216
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As much of the media keeps talking about "hearing" the pinger, and the pinger transmitting at 37.5 Kilohertz, which is inaudible to humans, might wonder how to make it audible.

The process is called heterodyning. Which is locally generating a frequency and mixing it with the expected pinger frequency. Thus if locally we generate say a 30 Khz frequency and running it through mixer and the other input to the mixer is the pinger's 37.5 khz the resulting output will be the sum and the difference of the two signals. Thus the output will contain the sum 67.5 Khz and difference of 7.5 Khz.

Filtering out 67.5 Khz which is of no immediate use, and amplifying the 7.5 Khz which is audible, passing it to aloudspeaker or headphone makes it human useable.

As some media noted the actual pinger frequency found was at 33 Khz, using the above method the audible frequency would be correpondingly lower.

In the detecting equipment they usually have a spectrum analyzer, which would show the received pinger signal as pip on a scope output.

Currently they have not picked up anymore signals, or if did, are keeping mum.
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Old 04-08-2014, 11:47 AM   #217
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As much of the media keeps talking about "hearing" the pinger, and the pinger transmitting at 37.5 Kilohertz, which is inaudible to humans, might wonder how to make it audible.

The process is called heterodyning. ...
Hetrodyning is certainly one way to do it, and might be what they are doing. But I'd think with today's technology, they'd use some digital filtering and attempt to accumulate the signal, which can effectively increase the signal/noise ratio.

My earlier link says the 'ping' is 10 mSec duration. So the signal repeats 375 times in just one 'ping'. And they might be able to accumulate the pulses from the next ping a second later. If they can accumulate just 200 cyles, that raises the power level by 20db above the noise, every additional ping would add another 3db (or maybe 40 and 6, not sure this applies to voltage or power in this application - hmmm, actually less I think, it is the difference between the correlated signal and non-correlated noise, but that is the concept). It only works with a signal that repeats.

I was surprised to see some refs saying one signal they picked up was 33Khz, and they thought that was a reasonable amount of drift. Even my linked spec sheet says +/- 1KHz, which is very loose with today's technology. I would think they would go crystal controlled, which even the cheapest ones non-temperature compensated, get you to about 200 ppm, so about +/- 10 hertz (going by memory here on the 200 ppm figure). It would be easier to detect if a more exact frequency was known. I was thinking that maybe a xtal osc would draw more battery current, but heck, that is what we have in digital wrist watches, and those go over a year on a very small cell.

Non-technical explanation of above 'accumulation': Imagine someone writes the letter "A" on a piece of paper that is covered with dots and lines (noise), but writes so lightly, or just puts a few dots down at a time, that it is not discernible as a letter "A" at all. Now imagine they repeat that 200 times - the "A" will start to appear from out of the background of dots and lines. That is what accumulating a signal does.

-ERD50
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Old 04-08-2014, 01:15 PM   #218
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It would be nice to find the actual pinger circuit. My guess it is using the KISS formula, the simplest RC stuff with precision resistors. Which would explain the huge frequency drift.

Maybe even a Piezo disc gated by relaxation oscillator. My SWAG.
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Old 04-08-2014, 01:37 PM   #219
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Here is a description from Teledyne Benthos:


"Theory of Operation

The printed circuit board assembly generates all the necessary logic functions
to produce a pulse with the desired char
acteristics. The pulse is then
transformed from a CMOS level square wave to a much larger 37.5 kHz
sinusoidal pulse by a transformer. T
he output of the transformer drives the
urethane-encapsulated transducer, whic
h propagates through the housing in
the form of a tuned 37.5 kHz acoustic signal."
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Old 04-08-2014, 02:34 PM   #220
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Non-technical explanation of above 'accumulation': Imagine someone writes the letter "A" on a piece of paper that is covered with dots and lines (noise), but writes so lightly, or just puts a few dots down at a time, that it is not discernible as a letter "A" at all. Now imagine they repeat that 200 times - the "A" will start to appear from out of the background of dots and lines. That is what accumulating a signal does.

-ERD50
Thanks, ERD50 for the explanation. I've been following this thread (or, at least trying to follow the thread) and sometimes I get a bit lost.
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