I have an adapter which on 1 side offers an RJ11 male plug, and on the other side and USB Type A female port, I also have another adapter which is similar but it offers and USB Type A male plug.

I would like to connect this to my computer and connect to the internet from there, removing the need for an external modem, anyone knows about how the drivers or the routing should be configured in this case ?


here is a picture of what I have


here are the other sides

enter image description here

of course this is the variant with the female USB, I have one with a Type A male plug as well.


If that truly is just a cable adapter, with no electronics hidden underneath that black overmolding, you're not going to be able to use it to connect to the analog telephone network.

USB uses its four wires for power, ground, and a differential signaling pair, all operating at 5 V DC.

POTS uses its four wires as two separate phone lines, with voltages up to 48 VDC. There's phantom power riding on those lines, and the audio signal is modulated on top of that voltage.

This vast difference between computer data signaling and analog phone signaling is the very reason we have analog telephone modems: they convert the signaling scheme from one format to the other, and vice versa.

If you use one of those adapters to plug a live analog telephone line into your computer, you're likely going to blow up the USB port.

The only reason those adapters exist is so you can transport USB over cheap wiring, especially existing wiring. They won't be any good for high-speed USB with most phone cable, and won't be good for much distance besides.

There are commercially-available USB analog telephone modems, compatible with Linux and OS X at least. You just plug them into the USB port and they appear as /dev/ttyUSB0 or /dev/ttyACM0 on Linux, meaning the OS sees them as USB-to-serial adapters. You configure them for PPP the same as you would any old-school RS-232 serial port, like /dev/ttyS0 on Linux.

  • I'm assuming that this is the same reason why you can't mix AC and DC ? – user2485710 May 9 '14 at 6:13
  • @user2485710: You can mix AC and DC. Analog telephone systems use DC for power, and AC for voice signaling and for the ring voltage. The ring voltage is fairly high AC, high because originally it had to drive the mechanical bell inside the telephone receiver. (Having been zapped by it a few times, I can tell you that it's high enough voltage to hurt!) The problem isn't mixing AC and DC. It's attempting to get a 5V USB port to put out the +/-48V needed by POTS, and getting it to not blow up when receiving that high voltage. It's apples and oranges, is what it is. – Warren Young May 9 '14 at 6:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.