Cordless Telephones
What Is A Cordless Telephone?
A cordless telephone consists of two parts
Base station:
The base station is connected to the land line socket/jack using standard telephone patch cord. The base receives the call signals and transmits to the handset over wireless using first radio frequency using FM (Frequency modulation) technique. The base station requires power from mains.
Handset
The handset receives the wireless signal from the base and converts the wireless signal to electrical voice signal which is sent to the earphone or speaker for listening. On the other hand the mouthpiece picks up the voice signal and the handset transmits the signals using second radio frequency using FM to base station for onward transmission to telephone line. The handset is powered by rechargeable batteries. The handset batteries gets recharged when it is put on the base cradle.
History Of Cordless Phones
The first cordless phone was invented by a jazz musician named Teri Pall in 1965. She could not market it. The patent for first cordless phone by George Sweigert was patented as "full duplex wireless communications apparatus" in 1966.
Frequencies for Cordless Telephones
The following frequency band allocated by Federal Communications Commission for cordless telephones are mostly used now a days:
- 900 MHz (902–928 MHz) (allocated in 1990)
- 1.9 GHz (1880–1900 MHz) (used for DECT communications outside the U.S.)
- 1.9 GHz (1920-1930 MHz) (allocated U.S. in October 2005)
- 2.4 GHz (allocated in 1998)
- 5.8 GHz (allocated in 2003 due to crowding on the 2.4 GHz band).
Major Features to look for while selecting phone
The main features to look for in cordless phones are:
Range:
The range is the distance that the handset can be from the base without affecting the quality of signal. The range depends on the frequency used, the number of channels and the analog or digital technology used. The lower frequencies and digital technology provide higher range. However, higher range is a security threat as the signal can be picked up by any one lese out side the premises where the phone is installed.
Sound Quality:
The sound quality depends on the technology as well as the wireless system used. The digital technology provides better quality.
Security:
The security feature of phone is important so that no outsider can eavesdrop on the conversation. Digital technology offers better security. The phones with digital spread spectrum (DSS) offer better security. DSS spread the digital information in parts over several frequencies between the receiver and the base, thereby making it very difficult to eavesdrop on cordless phone conversations.
Battery:
The rechargeable batteries used in cordless phones are Nickel-cadmium, nickel-metal hydride, lithium. The Ni Cd batteries have memory effect. The Nickel-metal hydride and lithium batteries have no memory effect and are superior to NiCd batteries.
