How does a Phone Work?

Eric Tallberg

The essential electro-mechanical functions that make a phone work are fairly simple and straightforward. This explanation describes the processes that make a land-line phone work. The processes that make cell phones work and that allow Voice over Internet Protocol (VoIP) telephones to work, are a bit more complicated, necessitating radio waves and Internet Protocol (IP). The basic principles to make any phone work, however, are the same.

Businesses use phones every day.
Businesses use phones every day.

To make a landline phone work, two copper wires must transmit two things: signals and voice. The two wires, usually coated green and red, are the heart of the process that makes the phone work. While the telephone rests on the hook or in its cradle, a capacitor inside the phone cradle limits the amount of electrical current flowing to the ringer, actually a chip within a small speaker. The capacitor prevents a short circuit in the wires and the local telephone exchange equipment recognizes that the phone is hung up.

Satellite phones rely on a satellite network to transmit signals.
Satellite phones rely on a satellite network to transmit signals.

For proper phone operation, sound must be conveyed along the same wires that activate the ringer. The handset of all telephones contain a microphone that allows sound pulses to be transferred into electrical pulses. The other integral part of the handset, the receiver, converts the audibly modulated electrical current back into sound waves and the voice is heard. Transmission and reception of the voice, therefore, depends on both sound waves and electrical pulsation.

Telephone cables strung on telephone poles convey calls to the local exchange.
Telephone cables strung on telephone poles convey calls to the local exchange.

When the phone is in its cradle, only the ringer, the chip, is connected electrically. When the phone receives an incoming call, the local telephone exchange is sending a high voltage alternating current (AC) surge to the cradle switch. This surge overrides the capacitor and the cradle’s integrated circuitry (IC) causes the phone to ring. For telephones in the U.S., this surge is usually in the range of 20 hertz (Hz). The phone receiving the call is selected via the dial tone multi-frequency (DTMF) pulses, the buttons on the calling party’s telephone keypad. When transmitting and receiving handsets are picked up, the switch in the cradle transfers the electrical surges from alternating current to direct current (DC), allowing voice transmission over the two wires. The two cradle switches then energize resistance shorts across their respective wires, producing a dial tone at the transmitting end and activating the ringer at the receiving end.

The thelephone's primary wires run from phones to phone-jacks and to the entrance boxes at the home or building. From there, phone cables strung on the ubiquitous telephone poles along the street convey calls to the local exchange. From the local exchange, fiber-optic lines, radio transmission and, for long distance calls, satellite transmissions carry a call to its destination where it ends up back within the two copper wires.

Radio waves are used to make a cell phone work properly. Internet Protocols (IP), network digitizing and packet switching are utilized to make the VoIP telephone work.

Landline phones use copper wires to transmit signals and voice.
Landline phones use copper wires to transmit signals and voice.

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Discussion Comments

I can foresee a day when land line telephones will no longer be in service, but I would hate to see them go away completely. I remember a few times in recent years when my cellphone service was completely knocked out during a bad storm. The relay towers were damaged, too. The one thing that still worked was my land line phone, so I was able to check on relatives and let everyone know I was safe.

I remember when I was young, I took an old rotary telephone apart to see how it worked. I was surprised to find all of these pieces of black gravel in the mouthpiece. I found out later that the "gravel" was actually pieces of carbon, and they gave off an electrical charge whenever someone spoke into the mouthpiece. The vibrations from a voice would create variable pulses of electricity, and that's what went into the outgoing wire.

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