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

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.

On 11/10/2011 4:23 PM, glen herrmannsfeldt wrote:
> Rune Allnor<allnor@tele.ntnu.no>  wrote:
>
> (snip, someone wrote)
>>>> it would be really rewarding for someone to develop an
>>>> emergency comm system for miners trapped underground...
>
> (snip)
>> You might want to take a long and hard look at the prioirities,
>> what functionality is actually *needed* and what is merely
>> *convenient*?
>
>> The *necessary* properties are simple. The system needs to
>
>> 1) Communicate that somebody is still alive in the mine.
>> 2) Be used for locating where the transmission originates from.
>
> So, either direction finding (hard at low frequencies) or enough
> bits of information and a map.
>
> Should be low enough cost that it can be used in poor countries.
>
>> Anything else, even acknowledgemnts of messages recieved, are
>> mere conveniences that kan be skipped with no *essential* loss.
>
> Hmm.  Remembering the Chile mine rescue, they first drilled a
> small enough hole to be sure someone was alive, get food and
> water down.  It might have been nice to notify the miners
> that help was coming.  That is, so they don't get discouraged.
>
> But that only takes one bit.

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

> It would seem that more power would be available on the surface,
> though also one could build more sensitive receivers, and use bigger
> antennae.
>
>> If one limits the scope of the system to the two items above,
>> one all of a sudden can make efficient systems at least on
>> the workstation / squad level; maybe even personal systems.
>
> -- glen


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

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.

Fred

Rune Allnor <allnor@tele.ntnu.no> wrote:

(snip, someone wrote)
>> >it would be really rewarding for someone to develop an 
>> > emergency comm system for miners trapped underground...

(snip)
> You might want to take a long and hard look at the prioirities,
> what functionality is actually *needed* and what is merely
> *convenient*?

> The *necessary* properties are simple. The system needs to

> 1) Communicate that somebody is still alive in the mine.
> 2) Be used for locating where the transmission originates from.

So, either direction finding (hard at low frequencies) or enough
bits of information and a map.

Should be low enough cost that it can be used in poor countries.

> Anything else, even acknowledgemnts of messages recieved, are
> mere conveniences that kan be skipped with no *essential* loss.

Hmm.  Remembering the Chile mine rescue, they first drilled a
small enough hole to be sure someone was alive, get food and
water down.  It might have been nice to notify the miners
that help was coming.  That is, so they don't get discouraged.

But that only takes one bit.

It would seem that more power would be available on the surface,
though also one could build more sensitive receivers, and use bigger
antennae.

> If one limits the scope of the system to the two items above,
> one all of a sudden can make efficient systems at least on
> the workstation / squad level; maybe even personal systems.

-- glen

On 11/10/2011 2:25 PM, glen herrmannsfeldt wrote:

   ...

> So, no 7Hz transmitters?  That was the story I remembered.

Maybe that came later

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

On Thu, 10 Nov 2011 11:03:56 -0600, Tim Wescott <tim@seemywebsite.com>
wrote:

>On Thu, 10 Nov 2011 00:07:01 +0000, Eric Jacobsen wrote:
>
>> On Wed, 9 Nov 2011 18:49:19 -0500, "MarkK" <makolber@yahoo.com> wrote:
>> 
>> 
>>>
>>>> The OP could state just how "open air" it needs to be?  I suspect you
>>>> could do a lot better if the user was expected to hold the phone up to
>>>> the speaker than if it had to work from across the room.
>>>
>>>
>>>speaking of difficult channels
>>>
>>>it would be really rewarding for someone to develop an emergency comm
>>>system for miners trapped underground...
>>>
>>>Mark
>> 
>> There are standards for such things, and products that meet the
>> standards.   I don't know how well any of them work in practice, but
>> some seem to be pretty useful.
>> 
>> We did some consulting for these guys several years ago for some early
>> work on a magnetically-coupled system:
>> 
>> http://www.kuttaradios.com/
>> 
>> The idea is to use magnetic coupling to existing infrastructure, pipes,
>> rail, cables, whatever.  Naturally, if such infrastructure isn't in
>> place or gets disconnected in an event, it won't be useful.
>> 
>> There are other approaches as well, some using traditional radio
>> techniques, but it's a difficult proposition to make something that will
>> work in all cases.   The through-the-ground stuff is probably not
>> practical, either.
>> 
>> Over the years and especially lately I've spent a fair amount of time in
>> an extensive tunnel network in a silver mine.  Recently I took some FRS
>> radios in there with me, keeping my fingers crossed that the tunnels
>> would provide some degree of waveguide or power concentration effect,
>> but the range of the radios was about the same range as just shouting at
>> each other, so it didn't work well at all.   I have some ideas of how to
>> make that better, especially around corners, but haven't had a chance to
>> try anything yet.
>> 
>> It is a difficult and interesting problem.   I'm hoping to use the
>> access to the tunnels for some experiments, but won't be back in there
>> until next year.
>> 
>> 
>> Eric Jacobsen
>> Anchor Hill Communications
>> www.anchorhill.com
>
>If it works well and you commercialize it, you'll need to change your 
>name to "Under Hill Communications"

The name "Anchor Hill" comes from the historic location of an
underground gold mine, coincidentally.  ;)

The other day I found out that a client is entering the underground
(mining) comm business.   I told them I have a test facility available
if they're interested.   I'm hoping that works out.  ;)


Eric Jacobsen
Anchor Hill Communications
www.anchorhill.com

On 10 Nov, 01:07, eric.jacob...@ieee.org (Eric Jacobsen) wrote:
> On Wed, 9 Nov 2011 18:49:19 -0500, "MarkK" <makol...@yahoo.com> wrote:
>
> >> The OP could state just how "open air" it needs to be? &#4294967295;I suspect you
> >> could do a lot better if the user was expected to hold the phone up to
> >> the speaker than if it had to work from across the room.
>
> >speaking of difficult channels
>
> >it would be really rewarding for someone to develop an emergency comm system
> >for miners trapped underground...
>
> >Mark
>
> There are standards for such things, and products that meet the
> standards. &#4294967295; I don't know how well any of them work in practice, but
> some seem to be pretty useful.
...
> It is a difficult and interesting problem. &#4294967295; I'm hoping to use the
> access to the tunnels for some experiments, but won't be back in there
> until next year.

You might want to take a long and hard look at the prioirities,
what functionality is actually *needed* and what is merely
*convenient*?

The *necessary* properties are simple. The system needs to

1) Communicate that somebody is still alive in the mine.
2) Be used for locating where the transmission originates from.

Anything else, even acknowledgemnts of messages recieved, are
mere conveniences that kan be skipped with no *essential* loss.

If one limits the scope of the system to the two items above,
one all of a sudden can make efficient systems at least on
the workstation / squad level; maybe even personal systems.

The basic principle is simple, although implementation might
require some work. The key is to think in the correct terms,
focus on the essentials, and otehrwise keep the relevant
perspective.

Rune

Jerry Avins <jya@ieee.org> wrote:

(snip in submarine radio)

> Not merely a dielectric, but a very lossy one. Actually, 
> a fairly good conductor.

(snip)
>   ...

> The US navy's ELF carrier frequency was 67 Hz. (Not a typo.) The 
> Russians' was higher: 82 Hz. The US antenna (at Clam Lake, Wisconsin?) 
> was only 32 miles long. There was a dedicated power plant to power it, 
> and in the end it radiated only a few watts.

> The names "Sanguine" and "Seafarer" come to mind.

I wonder how much 60Hz there is down there.  I would have thought
that 67Hz wouldn't be a good choice in a 60Hz world, but maybe not
so bad in a 50Hz world.

I remember one homework problem with a submarine and long wire
antenna at 15kHz, using 9 for the index of refraction (sqrt(80)).
For that, the submarine has to come close to the surface, but
not actually above the surface.

So, no 7Hz transmitters?  That was the story I remembered.

-- glen

On Thu, 10 Nov 2011 00:07:01 +0000, Eric Jacobsen wrote:

> On Wed, 9 Nov 2011 18:49:19 -0500, "MarkK" <makolber@yahoo.com> wrote:
> 
> 
>>
>>> The OP could state just how "open air" it needs to be?  I suspect you
>>> could do a lot better if the user was expected to hold the phone up to
>>> the speaker than if it had to work from across the room.
>>
>>
>>speaking of difficult channels
>>
>>it would be really rewarding for someone to develop an emergency comm
>>system for miners trapped underground...
>>
>>Mark
> 
> There are standards for such things, and products that meet the
> standards.   I don't know how well any of them work in practice, but
> some seem to be pretty useful.
> 
> We did some consulting for these guys several years ago for some early
> work on a magnetically-coupled system:
> 
> http://www.kuttaradios.com/
> 
> The idea is to use magnetic coupling to existing infrastructure, pipes,
> rail, cables, whatever.  Naturally, if such infrastructure isn't in
> place or gets disconnected in an event, it won't be useful.
> 
> There are other approaches as well, some using traditional radio
> techniques, but it's a difficult proposition to make something that will
> work in all cases.   The through-the-ground stuff is probably not
> practical, either.
> 
> Over the years and especially lately I've spent a fair amount of time in
> an extensive tunnel network in a silver mine.  Recently I took some FRS
> radios in there with me, keeping my fingers crossed that the tunnels
> would provide some degree of waveguide or power concentration effect,
> but the range of the radios was about the same range as just shouting at
> each other, so it didn't work well at all.   I have some ideas of how to
> make that better, especially around corners, but haven't had a chance to
> try anything yet.
> 
> It is a difficult and interesting problem.   I'm hoping to use the
> access to the tunnels for some experiments, but won't be back in there
> until next year.
> 
> 
> Eric Jacobsen
> Anchor Hill Communications
> www.anchorhill.com

If it works well and you commercialize it, you'll need to change your 
name to "Under Hill Communications"

-- 
www.wescottdesign.com