du4@mace.cc.purdue.edu (Ted Goldstein) (11/01/90)
Hello all,
I am trying to build an external acoustic coupler for a direct
connect modem so it can be used with a foriegn phone system and I need
some phone gurus to tell me if my idea is possible or not. Basically
my setup is as follows:
_____ _____
| | | |----------\ To phone line
| __| |__ |----------/
| | | |
________ ________ | | | |
| | | | | |__ __| |
| PC | - - -|Modem |---------------| | | |
| | | |---- --------| A | | B |
-------- -------- | | ----- -----
+9V Two phones taped
mic to speaker.
The idea is that the tones the modem puts out are converted to
acoustic by american phone 'A' and then converted back into phone line
signals by foriegn phone 'B'. The end goal is to use an American modem
in France.
I have tried this setup, and the modem does hear the dial tone, and
will attempt dialling, but can't hear the carrier from the answering
modem.
I am using el'cheapo (tm) phones for my tests, maybe they are
distorting the tones(?). Before I try again with better phones, I was
wondering if my theory is sound (no pun intended). Should this work?
I have also heard such a commercial device exists to accomplish this
task. Any leads on this would also be welcome.
Any information, thoughts, ideas or product leads would be greatly
appreciated!
Ted Goldstein E-mail: du4@mace.cc.purdue.edu
Network and Systems Admninistrator Phone : (317) 494-9070
Purdue University School of Technology Office: Knoy Hall, Rm G009julian@bongo.uucp (Julian Macassey) (11/05/90)
In article <14218@accuvax.nwu.edu>, du4@mace.cc.purdue.edu (Ted Goldstein) writes: > I am trying to build an external acoustic coupler for a direct > connect modem so it can be used with a foriegn phone system and I need > some phone gurus to tell me if my idea is possible or not. Drawing deleted >Two phones taped mic to speaker. > The idea is that the tones the modem puts out are converted to > acoustic by american phone 'A' and then converted back into phone line > signals by foriegn phone 'B'. The end goal is to use an American modem > in France. > I have tried this setup, and the modem does hear the dial tone, and > will attempt dialling, but can't hear the carrier from the answering > modem. More stuff deleted >Any leads on this would also be welcome. The "How do I connect my U.S. Modem to overseas phone lines FAQ" has reared its head again. First let me address the Acoustic Coupler thing. Basically, acoustic couplers are an "Okie fix". They are a chickenshit solution to the "Don't you dare connect anything to our equipment" bullying from telcos in the pre deregulation days. Before that starts a flamefest, I said deregulation, not divestiture. Acoustic couplers work some of the time with 300 baud FSK modems (Bell 103). They work every now and again with 1200 baud modems(Bell 212A, CCITT V22). How well they work depends on the angle at which you hold the handset when using carbon transmitters. Yes, using an electret transmitter works better with an acoustic coupler. It also depends on the level at which you transmit the tones into the transmitter and how well you detect them. The coupler should also shield out room noise, etc. This is all a tremendous pain in the arse and can be avoided with the solution presented below. But if anyone really wants to know how to build an acoustic coupler, I could tell them. I could even ship them a modem or two with the damn things built in. They are gathering dust in the garage/telco warehouse. The best way to couple a modem to the phone line is wire the damn thing to the phone line. This can be done to any phone anywhere in the world, despite what the superstitious natives may tell you. If you have a U.S. type phone, answering machine, dialer, modem or what have you, this is what you do: You need a line cord with a modular plug on one end and spade lugs on the other. Radio Shack part number 279-391 for the twelve foot jobbie. Ignore or remove the two outer wires and lugs. These may be a yellow and black wire. The two inner conductors carry the telephone signal and voltage. For extra versatility, you may want to buy a pair of Radio Shack Alligator clips, Part Number 270-346. These are also known as crocodile clips or roach clips depending on whether you consort with colonials or dopers. They have a screw terminal on them so you can screw the line cord spade lugs on to them. Yes, you will need to know how to use a screwdriver. When in foreign lands, locate the jack or terminal block that the phone is connected to. Disassemble and using either a screwdriver to loosen screws and insert spade lugs or the clips to attach to exposed metal, make the phone connection. If you get dialtone, you have done it correctly. You may find that carrying a sleezoid one piece phone as a test set helps. Before you plug your equipment into the electrical socket check the voltage. Don't forget that in different lands they have different line voltages. The U.S. Gummint printing office has a nifty book on voltage levels and plugs. The book is Electric Current Abroad from the U.S. Dept of Commerce. I paid $2.50 for mine at the U.S. Gummint printing office, the parking was $6.00. Julian Macassey, n6are julian@bongo.info.com ucla-an!denwa!bongo!julian N6ARE@K6IYK (Packet Radio) n6are.ampr.org [44.16.0.81] voice (213) 653-4495