Testing my telephone line.

Discussion in 'General Electronics Chat' started by jmoffat, Oct 11, 2016.

  1. jmoffat

    Thread Starter Member

    Jul 18, 2012
    Currently my house is not connected to a telephone network. I want to test all of my telephone circuits. I guess I need to send a audible tone on the wires plus some voltage to power the phone. So what voltage do I need to power a modern ( not rotary dial ) phone? I do not necessarily need to ring the the phone. I can simply plug in the phone and listen.
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Won't a simple resistance test do? Open/short at one end; check using DMM on Ohm's range at the other end.
  3. crutschow


    Mar 14, 2008
    Yes, all you need is a continuity test if you are just testing the wires.
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    A simple 12v psu adapter ( walwart) on the incoming cable terminals will do, then measure the voltage at each telephone socket.
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    Rotary or dial, they are all designed for the standard land line standards. Normal audio is -13 dbM at 600 ohms. The DC voltage is -48

    Sorry about that....fat fingers. P:)
    Last edited: Oct 12, 2016
  6. jmoffat

    Thread Starter Member

    Jul 18, 2012

    Thanks to Alec_t, crutschow, Dodgydave and KL7AJ for your replies. Yes I didn't really think it through. Trying to get voltage readings from a modular outlet is difficult. that's why I wanted to just plug in a phone. This morning I put together a 24v power supply a small relay and a Zip-Link module. The relay is wired as a buzzer and the Zip-Link provides screw terminal access to a modular outlet. Plug in a phone and the buzzing can be heard from the receiver. An RJ-12 jumper plugged into any modular outlet in the system will allow me to check the other branches. I used these materials because I have this stuff readily available at work. The whole thing is mounted to a scrap of Din rail. I will take my contraption home tonight and bring it back in the morning.
  7. dl324

    AAC Fanatic!

    Mar 30, 2015
    Phone companies in the US don't like you messing with things like that. Make sure you disconnect your network interface box from the phone line drop to your house.

    Even if the phone line is "disconnected", it could still be live. I have a second line at my house that was paid for by my previous company. It was "disconnected" over 10 years ago, but the line still works.
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
    Did you see his first post?

  9. dl324

    AAC Fanatic!

    Mar 30, 2015
    I did, but I had sufficient doubt about what he meant to post about disconnecting the network interface box.

    Better to be safe than sorry when applying power to phone lines.
  10. ian field

    AAC Fanatic!

    Oct 27, 2012
    Not quite - telephones are capacitively coupled, on hook - they only respond to AC such as the ring tone.

    Off hook, they draw a bias current - originally for the carbon granule mic, nowadays some simple circuitry around an electret mic. There's almost always at least a dialler chip and a simple regulator that can be as simple as a Zener and resistor.

    The exchange usually puts about 48V on the line.

    Over the years there have been a few magazine projects for phone test set boxes.