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2.4 GHz Phones
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A cordless telephone or portable telephone is a telephone with a wireless handset which communicates with a base station connected to a fixed telephone landline (POTS) via radio waves and can only be operated close to (typically less than 100 meters of) its base station, such as in and around the house. Unlike a standard telephone, a cordless telephone needs household mains electricity to power the base station. The cordless handset is powered by a battery which is recharged by the base station when the handset is connected to the base station when not in use.
Modern cordless telephone standards, like PHS and DECT, have blended the once clear-cut line between cordless and mobile telephones by supporting cell handover, various advanced features like data transfer and even, on a limited scale, international roaming. In these deployment models, base stations are maintained by a commercial mobile network operator and users subscribe to the service.
Frequencies
In the United States, there are seven frequency bands that have been allocated by the Federal Communications Commission for uses that include cordless phones. These are:
1.7 MHz (Up to 6 Channels, AM System);
27 MHz (allocated in 1980, Up to 10 Channels, FM System);
43–50 MHz (allocated in 1986, Up to 25 Channels, FM System);
900 MHz (902–928 MHz) (allocated in 1990);
1.9 GHz (1920-1930 MHz) (developed in 1993 and allocated U.S. in October 2005);
2.4 GHz (allocated in 1998);
5.8 GHz (allocated in 2003 due to crowding on the 2.4GHz band);
Virtually all telephones now sold in the US use the 900 MHz, 2.4 GHz, or 5.8 GHz bands, though some legacy phones remain in use on the 27 and 43-50 MHz bands. There is no specific requirement for any particular transmission mode on 900, 2.4, and 5.8, but in practice virtually all 900 MHz phones are inexpensive, bare-bones analog models; digital features such as DSSS and FHSS ae generally only available on the higher frequencies.
One must be very careful when looking to purchase 5.8 GHz phones. In actuality, only the high-end 5.8 GHz actually transmit completely on that frequency. Most so-called 5.8 GHz cordless phones transmit from base to phone on 2.4 GHz or 900 MHz, and then from phone to base on 5.8 GHz.
The recently allocated 1.9 GHz band is used by the popular DECT phone standard from Europe.
Performance
Communication companies usually advertise that higher frequency systems improve audio quality and range. However, in reality higher frequencies actually have worse propagation in the ideal case, as shown by the basic Friis transmission equation, and path loss tends to increase at higher frequencies as well. Other factors that determine quality and range are signal strength, antenna quality, and the method of modulation used.
Read more at Wikipedia.org
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