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Old 04-08-2014, 02:50 PM   #221
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Originally Posted by ls99 View Post
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."
You guys are giving me a headache. I'm in management. Understood all I needed to know when I heard the word 'pinger'.
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Old 04-08-2014, 03:03 PM   #222
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Quote:
Originally Posted by ls99 View Post
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."
Thanks, Is99 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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Old 04-08-2014, 03:53 PM   #223
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You guys are giving me a headache. I'm in management. Understood all I needed to know when I heard the word 'pinger'.
Eh, this is nothing. You should sit in on a discussion when Phds and engineers with masters degrees argue discuss a topic.. THAT gives headache.
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Old 04-08-2014, 07:52 PM   #224
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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.
Yes, since this has to withstand extreme environments, the KISS principal certainly applies. At first I was thinking that a xtal osc is so 'old school', that it would be plenty simple. But then, I'm pretty sure that a crystal is a relatively delicate device, less able to withstand the G-Forces of a crash than plain old Rs, Cs, and Ls. So maybe that's it.

BTW, I found a spec sheet for one of the 'ping' detectors, and it did appear to be a simple hetrodyne circuit. Maybe there are more advanced ones with digital filtering, I gotta believe the military uses these advanced systems, heck, a guy could probably cobble up one in an afternoon in a well equiped lab and a computer.


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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.
My pleasure. I learned long ago that the best way to test your understanding of something is whether you can explain it to someone to get them to understand it. Some of this stuff is getting fuzzy, so it's a good exercise for me.


BTW, this 'accumulation' technique is what GPS units use. The signals from those satellites are very, very weak by the time they reach a spot on Earth, and a handheld GPS has a small antenna that has to work in any orientation (omni-directional), instead of a big dish that can be pointed directly at a satellite (which makes a huge difference). So the GPS satellites send a repetitive signal that can be accumulated. There really isn't much info in those signals, the unit just has to lock on so it can get the timing. So repeating the same thing over and over again works for something like that. Wouldn't work for real-time radio broadcasts like we get on our car/home AM-FM radios.

-ERD50
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Old 04-09-2014, 08:27 AM   #225
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I also would have thought they'd just have a computer filtering out all by the 37.5 KHz, and beeping when it detected that, but I can see that the heterodyning has advantages, such as letting the human ear make the decisions. I wonder if what we're hearing in this video is heterodyned (using a Dukane Tester):

http://ac360.blogs.cnn.com/2014/03/2...ly-sound-like/

As for the signal being at 33 KHz instead of 37.5 kHz, perhaps they are figuring that as the battery voltage goes down, the frequency could change. I know that that is often not how things work, but perhaps when voltage is low, all bets are off. Easily tested.

In any case, although the members of the media have the intelligence of 12-year-olds when it comes to this stuff, we can be pretty confident that the submarine people, and the people on these ships know what they are doing. They've been highly motivated to do this audio analysis stuff for decades.

We just need a news service for engineer types.
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Old 04-09-2014, 10:37 AM   #226
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My latest theory. If reports of the route around Indonesia are right, then it looks like aircrew, I would venture the copilot, was in control. Whoever was headed for Perth. They failed to account for the increased fuel requirement of skirting Indonesia and ditched the aircraft. As it was such a rookie mistake, that is why I suspect the copilot. It could have been an intruders, but the lack of radio chatter or emergency squawk leads me to discount that.

So there is my today's speculation, and you did not have to watch CNN commercials to get it.
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Old 04-09-2014, 10:53 AM   #227
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I also would have thought they'd just have a computer filtering out all by the 37.5 KHz, and beeping when it detected that, but I can see that the heterodyning has advantages, such as letting the human ear make the decisions. I wonder if what we're hearing in this video is heterodyned (using a Dukane Tester):

What black box 'pings' really sound like – Anderson Cooper 360 - CNN.com Blogs

As for the signal being at 33 KHz instead of 37.5 kHz, perhaps they are figuring that as the battery voltage goes down, the frequency could change. I know that that is often not how things work, but perhaps when voltage is low, all bets are off. Easily tested.

In any case, although the members of the media have the intelligence of 12-year-olds when it comes to this stuff, we can be pretty confident that the submarine people, and the people on these ships know what they are doing. They've been highly motivated to do this audio analysis stuff for decades.

We just need a news service for engineer types.
Those receivers do appear to be hetrodyne circuits, simply 'mixing' the higher frequency down to a lower one.

That 33Khz signal sure seems awful far (12%) from the spec of 37.5KHz +/- 1% from the spec sheet I linked earlier. I don't think a low battery condition would affect frequency much, but maybe another engineer could chime in on this. It sounds like they use a simple R/C/L resonant circuit for the oscillator, and those components have near zero parameter changes over the voltages that would be used. Possibly the amplifier impedance changes with voltage, and that might 'pull' on the resonant circuit, but I'm thinking that would be a very minor effect (and accounted for in the +/- 1% spec).

Bottom line, I think 33KHz is suspicious.

HAh- real-time update - Just as I posted, they were interviewing a guy on the radio that said he contacted the company, and they said theses frequencies can 'wobble' as the battery dies. But I think that 33Khz signal was reported a while ago, when the battery should have still been good. I wonder how good the maintenance checks are? If they are lax, no one would know until something like this happens.

-ERD50
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Old 04-09-2014, 11:47 AM   #228
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The first reports of the signals were around that 30 day battery life timeline. So, the signal may started to wobble already. For lack of better explanation, I think it's plausible. I will take CNN's (their guests) word for it.

In the last 24 hours, they reported two more signal finding although weaker, and for shorter durations. I think they now have enough data to narrow down the haystack area.
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Old 04-09-2014, 12:26 PM   #229
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We just need a news service for engineer types.
For this type of thing, the specialized print media still rules. But, we have to wait, and until then, the broadcasters will fill the void.
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Old 04-09-2014, 03:15 PM   #230
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Bottom line, I think 33KHz is suspicious.
This is a case where I'd say that the experts know the answer. The reporters might be getting it wrong, but I'm sure that the sonar guys will know if a 33 KHz signal is kosher.

In any case, it would only take minutes to take some pingers drop the voltage, and see what happens to the frequency. Might be a handy way of estimating the remaining life in the 370 pingers.
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Old 04-09-2014, 04:41 PM   #231
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This is a case where I'd say that the experts know the answer. The reporters might be getting it wrong, but I'm sure that the sonar guys will know if a 33 KHz signal is kosher.

In any case, it would only take minutes to take some pingers drop the voltage, and see what happens to the frequency. Might be a handy way of estimating the remaining life in the 370 pingers.
Agreed, it is certainly 'knowable' by the right people, running the right experiments, calculations, computer simulations, etc.

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Old 07-17-2014, 11:17 AM   #232
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Now another missing Malaysian flight. Likely shot down though.
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Old 07-17-2014, 11:19 AM   #233
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Now another missing Malaysian flight. Likely shot down though.
Malasia Airlines has got to be the unluckiest airline in the world. I can't imagine what family of those on that flight are going through.
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Old 07-17-2014, 11:23 AM   #234
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Two in less than 6 months? What is going on?
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Old 07-17-2014, 12:20 PM   #235
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I don't see the Malaysian airlines link as significant, assuming it was shot down.

But it does make me realize, as Bob Schieffer said on the news last night, what a remarkable amount of turmoil there is in the world today. Crimea, Israel, ISIS, Egypt, Iran, North Korea, and Afghanistan.
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Old 07-17-2014, 12:36 PM   #236
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I don't see the Malaysian airlines link as significant, assuming it was shot down.

But it does make me realize, as Bob Schieffer said on the news last night, what a remarkable amount of turmoil there is in the world today. Crimea, Israel, ISIS, Egypt, Iran, North Korea, and Afghanistan.
Probably can toss China and Vietnam in there somewhere as they have been squabbling over territorial waters.
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Old 07-17-2014, 12:53 PM   #237
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Probably can toss China and Vietnam in there somewhere as they have been squabbling over territorial waters.
China has territory squabbles with just about every adjacent countries big and small.

Given a choice, should/would one pick Malaysian plane to fly or go with another airline even if it costs more. Bad break for Malaysian airline but something for would be passengers to think about.
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Old 07-17-2014, 07:23 PM   #238
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Given a choice, should/would one pick Malaysian plane to fly or go with another airline even if it costs more. Bad break for Malaysian airline but something for would be passengers to think about.
There are a handful that you would never catch me on.
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Old 07-17-2014, 08:12 PM   #239
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The news tonight said it only took about 30 seconds from from missile launch to striking the plane. Pretty crazy. The plane was up at 33,000 ft.
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Old 07-17-2014, 08:54 PM   #240
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I'm watching Australian TV (ABC) and their commentators are pointing at a Russian made BUK missile launcher. There are audio clips of pro Russian rebels talking "Were there any weapons on board?, Civilians?"

Reports of 150 Dutch on board?
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