Cordless Telephone Frequencies
A cordless telephone is a portable telephone invented in 1965 by Jazz musician Teri Pall although the first person to be awarded a patent in 1969 was a US Army radio operator named George H. Sweigert. The cordless telephone is differentiated from a mobile phone by its base station which is connected to a fixed telephone line the same way a corded telephone is. The cordless telephone is made up of a wireless handset that communicates via radio waves and a base station. The differentiation between the corded and cordless phone is in the fact that the cordless telephone’s base is powered by (AC) electricity and its handset is powered by batteries.
How a cordless telephone works
- The base station is attached to the phone jack through a standard phone wire connection.
- The base receives the incoming call as an electrical signal through the phone line, which is converted to an FM radio signal and broadcasted to the handset.
- The handset receives the radio signal from the base, converts it to an electrical signal and sends that signal to the speaker which comes out as an audible sound.
- In conversation the handset broadcasts the sounds through a second FM radio signal back to the base.
- The base receives the voice signal, which is converted to an electrical signal and sent through phone line to the other party.
Analog vs. digital cordless telephones – Apart from transmitting sound on a designated radio frequency, the cordless phone also transmit in analog or digital format, depending on the model. Analog phones transmit using electronic pulses whilst digital transmission uses binary codes. Digital cordless phones provide a stronger, clearer signal with enhanced security as they are less prone to static and interference.
Frequencies used for cordless telephones
The cordless telephone operates on several radio frequencies. The base and handset operate on a frequency pair that allows persons to talk and listen at the same time, this is called duplex frequency. The range between the handset and base of the cordless telephone is dependent on the frequency available, that is, the functionality and call quality of the phone is dependent on the frequency or frequencies used.
The first set of cordless phones on the market was analogue using a frequency range of 27-30 megahertz (MHz); later models used 43-50 MHz which could be picked up on radio scanners and were therefore insecure.
The frequency range of 900 MHz was introduced in 1990 when the 43-50 MHz range became overcrowded. The 900 MHz frequency improved call quality, gave a longer call range and increased channels. This higher frequency is currently the most common frequency used for cordless telephones.
Digital cordless phones were introduced in 1994, and with the introduction of digital spread spectrum (DSS) in 1995 and the 2.4 GHz range in 1998, users were able have secured phone conversations over greater distances. Currently the highest ranges are 2.4 GHz and 5.8 GHz which minimize static caused by objects and interference by other electrical signals. Each frequency range is further divided into channels ranging from 1 to 100 depending on the band.
In earlier days cordless phones were quite expensive. Now a cordless phone can be bought for as low as US $30; the higher the frequency band range the higher the price will be.
