Modem Communication without telephone?

[glenjoy]

Maybe some of you may react with crazy comments, but before that, may I say that I am not the proponent of this, I just want to ask your point of view.

So what do you think? Is it possible to connect two modem directly by wire not through the PSTN, and make them communicate?

 

[bobcat1]

Hi

The answer is YES and i have done it befor 8O

You have to emulate the PSTN network for the modem to think it's connected

You will need to use a 24-48 V DC supply and a ring generator

All the best

Bobi

 

[glenjoy]

So how to dial on the other party?

 

[Guest]

Hi

You don't have to dail - only good for the PSTN use AT command

and the ring generator to start the modem working

All the best


Bobi

 

[glenjoy]

how about the dial tone?

Added after 2 minutes:

Btw, if the mods can move this thread to the microcontrollers section, because I think this proposal is not a joke anymore.

Thanks.

 

[klug]

Moved from "General" section.

There is a special mode to communicate two modems through direct line, or as it called "dedicated line". It is point-to-point connection without any PSTN.

You need to read mannual to find AT commands to switch yor modems in this mode. No ring generator or 60V supply is needed.

For example there is a string for Courier modem:

AT&B1&S2&H1&L1&W

You see &L1 command is mean - take line after modem power on, and reconnect after every disconnection.

So, you see - modem will not dial at all and no ring generator will need.

Also you need to set one modem as master - it will call, and other as slave - it will reply. There is a switch for this setting in Courier modems.

I do not know if your modem has this feature - read mannual.

Added after 4 minutes:

There is a FAQ for this mode:
https://www.usr.com/support/doc-popup-template.asp?url=faqs/analog/leaseline.html

 

[glenjoy]

Thanks fot moving the thread, but why here at PC interfacing, I am planning to interface it to microcontroller.

Btw, how many meters do you think it can support withput PSTN.

 

[klug]

You need to use twisted-pair cable for long distance connection. Maximal distance will be near 30-60 km in 19.200 kB/s, it will depend of line quality.

 

[glenjoy]

You need to use twisted-pair cable for long distance connection. Maximal distance will be near 30-60 km in 19.200 kB/s, it will depend of line quality.

30 to 60 km? Man, that is a very long distance, I think the modems cannot drive signal that long.

Btw, my modem does not support the said tech note by US Robotics, as modems now have no DIP switches.

My distance target is MAX of 10km.