How Cordless Telephones Work

GE cordless phone, including handset and base unit

Inside the Phone Base

To illustrate the parts of a cordless telephone, we will show you the inside of this one from General Electric (GE). It was made in 1993 and operated in the 43-50 MHz range.

As mentioned above, all cordless phones have a base and a handset. Let's look at these parts individually.

Base - The base unit of the cordless phone is plugged into the telephone jack on your wall. If you open up the base and expose the circuit board, you see several components that carry out the functions of the base:

Phone line interface - receives and sends telephone signals through the phone line Radio  - amplifies signals to and from phone-line interface, user controls and speaker phone (if present) and broadcasts and receives radio signals to and from the handset Power - supplies low voltage power to the circuits and recharges the battery of the handset

How Cordless Telephones Work

Circuit board in the base of the GE cordless phone

Phone Line Interface

Phone line interface components do two things. First, they send the ringer signal to the bell (if it's on the base) or to the radio components for broadcast to the handset. This lets you know that you have an incoming call. Second, they receive and send small changes in the phone line's electrical current to and from the radio components of the base. When you talk, you cause small changes in the electrical current of the phone line, and these changes get sent to your caller. The same happens when the caller talks to you.

Radio Components

The radio components receive the electrical signals from the phone line interface and user controls (keypads, buttons). The radio components convert the signals to radio waves and broadcast them via the antenna. Radio components use quartz crystals to set the radio frequencies for sending and receiving. There are two quartz crystals, one for sending signals and one for receiving signals. Remember that the base and handset operate on a frequency pair that allows you to talk and listen at the same time (duplex). The radio components include an audio amplifier that increases the strength of the incoming electrical signals.

Power Components

A DC power cube transformer supplies the low voltage required by the electrical components on the circuit board. The power components on the circuit board work with the power cube to supply electrical current to re-charge the battery of the handset.

In addition to the above components, some bases also have audio amplifiers to drive speakers for speaker phone features, keypads for dialing, liquid crystal displays (LCDs) for caller ID, light-emitting diodes (LEDs) for power/charging indicators, and solid state memory for answering machine or call-back features.

Take a look inside the handset next.