"Vangelis Pantazis" wrote in message ...
Hello everybody !
Can somebody tell me the technical difference between analog phone lines
(PSTN) versus digital ones (ISDN or aDSL) ?
Is there any way to distinguise them with an electronic device ?
I've heard of these digital phone line tester but I'm not sure if this is
the one I'm looking for to build.

Any ideas ? Many thanks, in advance

V.P.

I have such a device made by IBM called a Line Current Checker P/N
16F1621. They came out with the device about 15 years ago when laptop
computers and digital phone system were meeting in motel rooms. If
you plugged one of these early laptops into a digital line it would
blow up the modem. The analog line is current limited to 100ma and
the digital is not. The device is 5 1/2 inch long and 1/2 inch square
with a clip to wear in your shirt pocket. It has a RJ11 phone plug on
one end to plug into the line you want to test. It has three LEDs
that are powered by the phone line. The first light (green)is labeled
OK and indicates that current is limited to 100ma or less. The second
light (Red)indicates current not limited, over 100ma. The third light
(green) labeled REV indicates that the tip and ring wires are
reversed. This device does not indicate performance of the line but
lets you know what type line it is before you plug your laptop in.

Van Gardner