Modulation/Signaling scheme for transfering information over an acoustic channel

On 11/10/2011 4:52 PM, Fred Marshall wrote:
> On 11/9/2011 4:07 PM, Rune Allnor wrote:
>> On 10 Nov, 00:00, Fred Marshall<fmarshallxremove_th...@acm.org>
>> wrote:
>>> On 11/9/2011 12:28 PM, Rune Allnor wrote:
>>
>>>> On 9 Nov, 21:26, Jerry Avins<j...@ieee.org> wrote:
>>
>>>>> How do you classify acoustic modems?
>>>
>>>> As an acoustic interface to an EM comm channel.
>>>
>>>> Rune
>>>
>>> Reminds me somewhat of the term: "external locus of control".... :-)
>>>
>>> I think the "acoustic interface" is an acoustic communication channel
>>> pure and simple. What else can it be?
>>
>> An minor acoustic component in an otherwise totally EM system?
>> In the EM case the modem would hardly be considered a major
>> part of the propagation channel, but rather a component in
>> the interface between the source of the signal, and
>> the waveform that propagates as EM waves from the antenna.
>>
>> Rune
>
> Rune,
>
> Well, if it were just a "transducer" then I'd likely agree. But it
> isn't. It includes a modem (modulator-demodulator), a selected coding
> scheme, a transmit encoder and transducer, a receive transducer and
> decoder (the transducers each have both roles), etc. etc. The physical
> length of the channel, the fact that it's relatively "tightly coupled",
> the physical size of the components on a comparative basis, minor vs.
> major, etc. etc. aren't the issue.
>
> WHAT EM waves? WHAT antenna? Such things are peripheral to the
> discussion at hand.

Don't you mean completely extraneous? Acoustic couplers were used to 
adapt voice telephone to digital communication.

Jerry
-- 
Engineering is the art of making what you want from things you can get.

Jerry Avins <jya@ieee.org> wrote:

(snip)
>> Hmm.  Remembering the Chile mine rescue, they first drilled a
>> small enough hole to be sure someone was alive, 

(snip)
>> But that only takes one bit.

> They lowered a note and the miners sent one up. Fortunately, 
> they knew how to read.

Hopefully they lowered a light, too.  

I remember at the time wondering how they felt in the time
between the collapse and the hole coming through.  Not knowing
if there would be any rescue attempt.  Wondering how long they
had in food, water, and air, and how slow they should use
them up.

-- glen