Will MJ work with old Western Electric phone?
Moderators: Bill Smith, Pilot
Will MJ work with old Western Electric phone?
I am thinking about getting a magicJack to use as a second phone line. Does it give enough power to ring the old-fashioned bells inside my Western Electric 500 set? Or, does anyone know the max ringer equivalence of the device? I know the rotary dial probably won't work; I will have to get a tone dialer to fix that problem.
As a retired telecom technician I would like to shed some light on the subject and history of the POTS (Plain Old Telephone Set) and MJ. Remember the MJ is marketed as a “multimedia” device not a telecommunication device. Therefore it is not subject to the technical or registration requirements by the FCC for devices connected to the PSTN (Public Switched Telephone Network).
The MJ attempts to emulate a telephone line from the CO (Central Office). This consists of two wires known as “tip” and “ring”. The terms are a holdover from years past when an operator would sit at a mechanical board and plug what looked like a phono plug into a hole or jack to complete the call circuit. The plug had a tip on the end then an insulator followed by a ring then another insulator followed by the remainder of the plug.
While the POTS is on-hook, across the two wires should be about 48VDC. During a ring signal the CO places a 20 cycle per second AC carrier (20Hz) on the wires which results in about 96VAC at 20Hz. You can get a good shock if you are holding the bare wires during a ring signal. The 20Hz is a holdover from years past when all Western Electric/Bell POTS had a mechanical ringer which usually consisted of two small bells and in between them was a mechanical arm or “clapper” that was driven by a coil transformer. During the ring signal the arm would move back and forth striking one bell then the other at…. you guessed it… 20 times a second. This resulted in the distinctive patented Western Electric Bell ring sound. Off-hook across the two wires should be about 7VDC.
In all fairness I must say I don’t own a MJ as of yet, but I find it improbable the MJ is able to produce those three voltages, on-hook 48VDC, ring signal 96VAC @ 20HZ and off-hook 7VDC while powered by a USB port. I can’t help think many users are having problems because they are not using a self powered, electronic ring telephone set such as a cordless. Also, for those trying to use the whole house wiring approach, this may work for a while but I would expect a hardware failure inside the MJ at some point due to impedance loading. The MJ web site recommends a line cord six feet at max.
If any tech types here have a digital volt meter with a freq counter it would be interesting to discover what the output of the MJ has for the three conditions. Be sure to use a high impedance digital volt meter if you want to test.
The MJ attempts to emulate a telephone line from the CO (Central Office). This consists of two wires known as “tip” and “ring”. The terms are a holdover from years past when an operator would sit at a mechanical board and plug what looked like a phono plug into a hole or jack to complete the call circuit. The plug had a tip on the end then an insulator followed by a ring then another insulator followed by the remainder of the plug.
While the POTS is on-hook, across the two wires should be about 48VDC. During a ring signal the CO places a 20 cycle per second AC carrier (20Hz) on the wires which results in about 96VAC at 20Hz. You can get a good shock if you are holding the bare wires during a ring signal. The 20Hz is a holdover from years past when all Western Electric/Bell POTS had a mechanical ringer which usually consisted of two small bells and in between them was a mechanical arm or “clapper” that was driven by a coil transformer. During the ring signal the arm would move back and forth striking one bell then the other at…. you guessed it… 20 times a second. This resulted in the distinctive patented Western Electric Bell ring sound. Off-hook across the two wires should be about 7VDC.
In all fairness I must say I don’t own a MJ as of yet, but I find it improbable the MJ is able to produce those three voltages, on-hook 48VDC, ring signal 96VAC @ 20HZ and off-hook 7VDC while powered by a USB port. I can’t help think many users are having problems because they are not using a self powered, electronic ring telephone set such as a cordless. Also, for those trying to use the whole house wiring approach, this may work for a while but I would expect a hardware failure inside the MJ at some point due to impedance loading. The MJ web site recommends a line cord six feet at max.
If any tech types here have a digital volt meter with a freq counter it would be interesting to discover what the output of the MJ has for the three conditions. Be sure to use a high impedance digital volt meter if you want to test.
Being an electrical engineer and knowing somewhat how old POTS phones work....
It would be impossible to have the MJ device produce 48 VDC off hook and 96 VAC at 20 Hz with enough current to ring a mechanical bell.
I've hooked up a couple of phone with mechanical bells and you can barely hear the clapper go back and forth. Most phones with electronic ringers (aka "bird chirp") work OK.
I don't have access to an O-scope anymore, but if I did I'd test the voltages just to see how much "jingle juice" that the MJ can provide. I know it can't be much.
It would be impossible to have the MJ device produce 48 VDC off hook and 96 VAC at 20 Hz with enough current to ring a mechanical bell.
I've hooked up a couple of phone with mechanical bells and you can barely hear the clapper go back and forth. Most phones with electronic ringers (aka "bird chirp") work OK.
I don't have access to an O-scope anymore, but if I did I'd test the voltages just to see how much "jingle juice" that the MJ can provide. I know it can't be much.