06-27-2023, 02:55 PM
(06-27-2023, 02:34 PM)Sagebrushdan Wrote: Or actually maybe you are right, I guess phone are powered off the phone jack itself.
There's 48VDC on the voice circuit (red and green wires) when the phone is off the hook. Very old phones from the 1800s had big dry batteries. Later, the exchange would send the 48VDC over the phone lines to every station.
The signal that rings the bell is 20Hz AC at 90V. It moves an electromagnetic hammer back and forth between two bells 20 times a second. Except the Princess ringer only had one bell on account of its size. That's why it sounds thin compared to the standard 500 series phones most people had.
The same 90VAC signal is still used to ring a remote station, even though it's converted to an electronic noise from a low-voltage chip in modern phones.
On a rotary dial, the number was sent by disconnecting and reconnecting the voice circuit from 1 to 10 times within a fixed interval, depending on the digit dialed. A governor on the dial made it take the same amount of time to dial any digit, regardless of how far the dial had to rotate. The pulses sent down the wire would move electromagnetic switches at the exchange to connect a route to the receiving end.
All of these signals were added at various times as technology developed. It's really quite amazing, considering this all happened before electronics existed. It's also cool that the same antiquated signalling system continued to be used as first analog and then digital electronics replaced the old electromechanical systems.
