United States In the United States, seven
frequency bands have been allocated by the
Federal Communications Commission for uses that include cordless phones. These are: • 1.7 MHz (1.665–1.770 MHz, narrow-band FM) Cordless phones manufactured after October 1, 1984, are not allowed to use this band and were required to use the newer (higher) 43-50 MHz frequencies, although older telephones, on the older frequency pairs, could still be used. • 27 MHz, near the Citizens Band (CB) Radio service with some frequencies being 26.010, 26.050, 26.380, 26.419 and 27.095 MHz. These were initially paired with the 1.7 MHz frequencies, then, later, with the 49 MHz frequencies. Signals were
FM - frequency modulation. • 43–50 MHz (Base: 43.72–46.97 MHz, Handset: 48.76–49.99 MHz, FM) Allocated in December 1983, and approved for use in mid-1984 for 10 channels. 15 additional channels allocated April 5, 1995. • 900 MHz (902–928 MHz, allocated in 1993) • 1.9 GHz (1920–1930 MHz, developed in 1993 and allocated in October 2005, especially with
DECT 6.0) •
2.4 GHz (2400–2500 MHz, allocated in 1998) • 5.8 GHz (5725–5875 MHz, allocated in 2003 due to crowding on the 2.4 GHz band) Over-crowding of earlier frequency allocations led users to discontinue using telephone equipment that operated on those frequencies, leaving those bands relatively clear. Radio hobbyists monitor usage of the older equipment with telephone activity in the US AM broadcast band, some 27 MHz frequencies and most older 43-50 MHz frequencies. 1.7 MHz cordless phones were the earliest models available at retailers, and are generally identifiable by their large metal telescoping antennas. Channels just above the
AM broadcast band were selected manually by the user. Some of the frequencies used are now part of the expanded AM radio band, and can be heard by anyone with an AM radio. There are reports of people still using these phones, and using them as makeshift AM radio stations that can be heard for a couple of city blocks. These models became obsolete because they are susceptible to eavesdropping, and interference from fluorescent lighting and automobile ignition systems. However, under ideal conditions they could have or more range. 43–50 MHz cordless phones had a large installed base by the early 1990s, and featured shorter flexible antennas and automatic channel selection. Due to their popularity, an overcrowding of the band led to an allocation of additional frequencies; thus manufacturers were able to sell models with 25 channels instead of just 10 channels. Although less susceptible to interference than previous AM units, these models are no longer in production and are considered obsolete because their frequencies are easily heard on practically any radio scanner. Advanced models began to use
voice inversion as a basic form of scrambling to help limit unauthorized
eavesdropping. These phones share the 49.8 MHz band (49.830 - 49.890) with some wireless
baby monitors. 900 MHz cordless phones are rarely sold but have a huge installed base. Features include even shorter antennas, up to 30 auto selecting channels, and higher resistance to interference. Available in several varieties; analog, analog spread spectrum (100 kHz bandwidth), digital, and digital spread spectrum, most being sold today are low-cost analog models, which are still susceptible to eavesdropping. Digital variants can still be scanned, but are received as a digital hiss and therefore are difficult to eavesdrop upon. Digital transmission is immune to static interference but can experience signal fade (brief silence) as the phone goes out of range of the base. Newer Digital Spread Spectrum (DSS) variants spread their signal over a range of frequencies, providing more resistance to signal fade. This technology enabled the digital information to spread in pieces among several frequencies between the receiver and the base, thereby making it almost impossible to eavesdrop on the cordless conversation. The FCC only allows DSS model phones to transmit at the full power of 1 watt, which allows increased range over older analog and digital models. Virtually all new cordless phones sold in the US use
DECT 6.0 on the 1.9 GHz band, though legacy phones can remain in use on the older 900 MHz, 2.4 GHz and 5.8 GHz bands. There is no specific requirement for any particular transmission mode on the older bands, but in practice many legacy phones also have digital features such as
DSSS and
FHSS. Some cordless phones formerly advertised as 5.8 GHz actually transmit from base to phone on 5.8 GHz and transmit from phone to base on 2.4 GHz or 900 MHz, to conserve battery life. The 1.9 GHz band is used by the
DECT 6.0 phone standard and is considered more secure than the other shared frequencies. The vast majority of new cordless phone devices sold in North America, whether connected by
landline or to mobile phones (usually via
Bluetooth), now use DECT 6.0. However, DECT 6.0's late start compared to DECT elsewhere has led to a large installed base of legacy cordless phones using other frequencies, many of which remain in use today despite increasingly common interference with the ever growing use of
Wi-Fi, Bluetooth and other unlicensed digital radio standards, especially at 2.4 GHz and 5.8 GHz.
Outside the United States In Europe, the 1.9 GHz (1880–1900 MHz) band was set aside for the
DECT phone standard from its inception. DECT, on its European band & related frequencies, has largely displaced all other cordless phone standards worldwide except for North America. == Performance ==