Acoustic couplers

[bellsystem]

I'm trying to find an acoustic coupler modem that can do higher than 300 bps.

Is there such a thing? From what I've picked up, people moved on from acoustic modems to electrical modem connections because of the speed restriction.

Are there any acoustic coupler modems that can do higher than 300bps? Or is there something about an acoustic coupler that prevents it from doing 300bps?

[TelePlay]

IIRC, Vadic and maybe AT&T made a 1200 Baud acoustic couplers but good luck finding this obsolete, '70s technology. The first direct connect modems started at 1200 Baud (I think I have one here somewhere) which quickly made the need for acoustic interfaces obsolete, unless you has a very poor copper phone line in some remote 3rd world country and were lucky to get a even 150 Baud.

The WE Data Phone was a 1200 baud direct connect device making acoustic, with all its issues and I used them, obsolete.

All this is readily available by way of a Google search, a great library to do your own research. Found this attached document with a single search of Google in just a few minutes.

I suppose you could really do some digging, find the schematic for a 1200 Baud acoustic  modem and tweak it to get a faster rate, if you really wanted one. The 300 baud boxes are readily available on eBay at times and could be refit with a circuit you designed to do a faster rate. I'm sure at some higher rate, you would end up with transmissions errors.

[Alex G. Bell]

IIRC, Vadic and maybe AT&T made a 1200 Baud acoustic couplers but good luck finding this obsolete, '70s technology. The first direct connect modems started at 1200 Baud (I think I have one here somewhere) which quickly made the need for acoustic interfaces obsolete, unless you has a very poor copper phone line in some remote 3rd world country and were lucky to get a even 150 Baud.

The WE Data Phone was a 1200 baud direct connect device making acoustic, with all its issues and I used them, obsolete.

All this is readily available by way of a Google search, a great library to do your own research. Found this attached document with a single search of Google in just a few minutes.

I suppose you could really do some digging, find the schematic for a 1200 Baud acoustic  modem and tweak it to get a faster rate, if you really wanted one. The 300 baud boxes are readily available on eBay at times and could be refit with a circuit you designed to do a faster rate. I'm sure at some higher rate, you would end up with transmissions errors.

As was discussed at some length back in some of BS's first threads about analog VS digital transmission methods, carbon transmitters inherently produce very high waveform distortion.  This ultimately limits the speed at which an acoustically coupled modem can operate because interfering harmonics of the signal frequencies applied to the reproducer in the coupler appear in the signal sent down the line.   

An acoustic coupler is essentially a kludge whose only valid use today probably would be at payphones.  It's a device which had no valid technical reason to ever exist other than the politics of the phone system monopoly.  With the elimination in the 1970s and '80s of the Bell System's monopoly position barring direct connection of customer owned modems to the telephone line virtually all acoustic couplers were in a single instant turned into junk. 

Other than impromptu data connections at public phones or nostalgia about the how screwed up things were before direct connection was permitted the only remaining valid application for them is in evaluating transmission performance of transmitters and receivers in handsets which fit them.

[bellsystem]

Thanks - I didn't know there were 1200b acoustic coupler modems,

Maybe I could go to the trouble of trying to engineering it faster.

A 1200b modem is probably plenty. Even a 300b modem is half-decent for text only transmission.

It's a device which had no valid technical reason to ever exist other than the politics of the phone system monopoly.

Well, I guess most people feel that way. Personally, I find the acoustic coupler a very ingenious contraption. It's certainly less complicated and easier to work with than modems connected electrically to a computer. And helpful for computers without Ethernet cards if you don't have an electrical/direct modem.

An acoustic coupler is essentially a kludge whose only valid use today probably would be at payphones.

[TelePlay]

Thanks - I didn't know there were 1200b acoustic coupler modems,

Maybe I could go to the trouble of trying to engineering it faster.

A 1200b modem is probably plenty. Even a 300b modem is half-decent for text only transmission.

Well, I guess most people feel that way. Personally, I find the acoustic coupler a very ingenious contraption. It's certainly less complicated and easier to work with than modems connected electrically to a computer. And helpful for computers without Ethernet cards if you don't have an electrical/direct modem.

1200 but not in full duplex mode as a 150 or 300 baud acoustic modem would be.

I don't see a distinction in that the acoustic modem converted the same data being sent electronically down telephone wire today into sound first using a speaker on one end and a receiver on the other ends to convert sound waves to electrical pulses. And, honestly, the higher the baud rate, the more likely the conversion won't be exact. Knowing the R&D process at production companies, the electronic modem was on the drawing board as soon as the acoustic modem was introduced, if not sooner. Your desire to utilize obsolete technology in this day and age, to re-invent obsolete equipment, mystifies me.

[bellsystem]

Might I remind you that the rotary telephone was invented long before the acoustic coupler. Funny people on this site don't call that obsolete.

[Alex G. Bell]

Might I remind you that the rotary telephone was invented long before the acoustic coupler. Funny people on this site don't call that obsolete.

The analogy does not work because rotary dial phones had a technological reason to exist at the time.  For the reasons I explained, acoustic couplers essentially did not have any technical justification.  They were a "techno-political" invention.

Odd that you have some kind of romantic attachment to acoustic couplers!

[Alex G. Bell]

Maybe I could go to the trouble of trying to engineering it faster.

Try?  Perhaps.  Succeed?  Very unlikely that someone who is not interested in anything beyond AC and DC circuits and does not understand or want to understand balanced and unbalanced circuits would be remotely capable of engineering much, let alone something this complex.

[Victor Laszlo]

Funny people on this site don't call that obsolete.

The rotary telephone is outdated.  It is replaced with better technology. People still use them.  It is not obsolete.

[Jim Stettler]

I received an acoustical coupler in the mail  today. This style is historically significant and are typically way overpriced. My example is cracked, but it was cheap and I always kinda wanted one.

http://www.ebay.com/itm/Vintage-Original-Carterfone-by-Carter-Electronics/253052298523


Jim S.

[bellsystem]

Hi Jim,
Cool find! But the link says Carterphone, is that also an acoustic coupler? Carterphones connect a phone to radio links.

[Alex G. Bell]

Hi Jim,
Cool find! But the link says Carterphone, is that also an acoustic coupler? Carterphones connect a phone to radio links.

Yes it's an acoustic coupler but for voice, not data.  The Carterfone is of great historical significance because it was the monkey wrench in the works which triggered the undoing of AT&T's monopoly.

AT&T prohibited the use of ANY KIND of ancillary device not provided by them with their telephone service.  This was stated in the front pages of the directory.  As absurd as it was, this included the use of telephone directory covers not provided by them, and in a very few cases they suspended peoples' service for such use.

AT&T's position was that if they did not offer the service, you could not have it: period.  In some parts of TX they did not provide mobile telephone service and some ranchers in these areas needed it.  Tom Carter designed, made and sold the Carterfone to satisfy this need by providing extension of phone calls out onto the range for these ranchers via private mobile radio.

AT&T's local operating company Southwestern Bell Tel. Co. took Carter to court and got an injunction against its sale.  Carter fought them to the highest courts and in 1969 The Carterfone Decision came down ordering AT&T to liberalize their policies by providing means for privately owned equipment to be connected to and used with their system.  The result is the free-market telephone industry we have today.   

Imagine if the electric company had required you to use their lamps and appliances, paying a monthly rent to have them, and you can understand the stifling effect AT&T's monopoly position had on the telecom infrastructure of the U.S.  Of course the computer industry had long been hampered by the requirement to use Bell System modems for high speed datacom beyond what could be accomplished with acoustic couplers, so there was a substantial body of evidence demonstrating the anti-competitive effects of AT&T's monopoly and prohibition on interconnection of customer owned equipment.

So unlike data acoustic couplers, the Carterfone is of great historical significance.  The ultimate irony of course is that when AT&T finally went bankrupt, what was SWBTCo. acquired the brand.  The AT&T of today is really SWBTCo AKA SBC.

[Jim Stettler]

Well stated Alex.


Jim S.

[Alex G. Bell]

Well stated Alex.


Jim S.

Thanks!

[TelePlay]

Alex, interesting. Knew of Carterphones but not the whole story.

Question, how did Ham radio guys get away with patching  telephone calls all over the world by way of shortwave radio? Was it because a home built radio was not a point source so not worth the expense of shutting one down when a guy down the block could do the same thing if need be?

Or something else?