Cordless phones first appeared around 1980. It wasn’t until 1994, however, that they became more affordable and reliable, using the 900-megahertz frequency. Cordless phones allow you to talk on the phone while moving freely about your house or in your yard. Basically, the cordless telephone is a combination telephone and radio transmitter/receiver.
There are two major parts: the base and the handset.The base is connected to the phone jack through a standard phone-wire connection and a power source. The base receives the incoming call as an electrical signal through the phone line, converts it to an FM radio signal, and then broadcasts that signal.
The handset receives that signal, converts it to an electrical signal and then sends that signal to the speaker, where it is converted into the sound you hear when the phone rings.
Talking into the receiver involves a second FM-radio signal being sent back to the base. The base reverses what it did originally, to send your voice to the calling party.
The base and handset operate on a frequency pair—called duplex frequency—that allows you to talk and listen at the same time.
Because cordless phones are a combination of a telephone and a radio transmitter/receiver, they are subject to similar problems as radio transmissions: range (the distance the handset can be from the base), sound quality, and security. Sound quality is related to range because the quality decreases the farther away from the base the handset travels. Security is a problem because the radio signals go over the open airways.
Cordless phones transmit their signals between the base and the handset wirelessly in two of the five available radio frequency bands using analog or digital technology (cordless phones use two closely related but separate frequencies within the band, so that you can talk and listen at the same time). These bands are set by the FCC (Federal Communications Commission) and are as follows:
1. The first cordless phones used a 43–50 megahertz band, and they are still available today in low-cost, low-range models. They generally have the poorest sound quality due to the low frequency and the interference from structures and appliances.
2. 900 megahertz is the most commonly used frequency and offers a good range. The problem with the 900-megahertz spectrum is that it is cluttered, which means interference problems can come from such other 900-megahertz products as baby monitors and radio scanners.
3. 2.4-gigahertz offers better clarity and security than 900-megahertz, but interference problems may occur from microwave ovens and wireless networking devices. Recent interference problems with 2.4-frequency analog phones have been eased somewhat by products that avoid portions of the 2.4 band used by wi-fi networks.
4. 5.8-gigahertz is used by the most advanced cordless phones. Generally, they will not interfere with wi-fi products, but be aware that some products billed as 5.8-gigahertz phones actually use both 5.8- and 2.4-gigahertz frequencies.
5. 1.9-gigahertz is used on DECT 6.0 devices and is becoming more and more popular as the 2.4 and 5.8 frequencies are increasingly overburdened. The 1.9 frequency has been used for many years in Europe but only recently approved in the United States. Because of the congestion of the other two frequencies, the 1.9 frequency is reserved for voice applications only. This was approved purposely to eliminate interference with wi-fi networks, the Bluetooth, baby monitors, and other wireless devices, and to increase clarity and security.
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