The working principle of cordless telephone
The cordless phone has the following questions: the limited scope of the sound quality difference due to the interference of the walls and home appliance to signal, causing the noise, static safety, because the channel limited number, it is easy to intercept signal from other cordless phone in 1986, the U.S. Federal Communications Commission (FCC) will allow 47-49MHz to provide the band cordless phone use, which not only improved the signal interference and their problems, but also reduce the power consumption. But these phones still have limited working distances and still have poor sound quality. With 43-50MHz's cordless phone band growing crowded, FCC offered 900MHz band in 1990. With this increase in frequency, cordless phones become clearer, spread farther, and more channels are available. But cordless phones are still very expensive and cost about $400. In 1994, a cordless cordless phone with 900MHz band was introduced. Digital signals improve the security of the phone and reduce the number of eavesdropping - eavesdropping on analog cordless phones is easy. In 1995, people began to apply digital spread spectrum (DSS) technology in cordless phones. This technique allows digital information to be transmitted across multiple frequency segments between the receiver and the landline, making it almost impossible for others to eavesdrop on the content of the cordless phone. In 1998, FCC opened the 2.4GHz band for cordless phones. This frequency not only increases the working distance of cordless phones, but also eliminates them from the frequency bands of most radio scanners, thus further improving the security.
When a handset receives a radio signal from a landline, it converts it to an electrical signal and sends it to the speaker, which is then converted by the speaker to the sound you hear. When you speak, your voice will hand opportunity through another FM radio signal propagation in the back plane; plane received voice signal after you will be converted into electric signals through the telephone line and sends the signals to each other. The frequency pairs used by landline and handset allow you to answer and answer calls simultaneously. This frequency is symmetrical for duplex frequency. Cordless phones first appeared around 1980. The earliest cordless phones work at a frequency of 27MHz.
Cordless phones are basically the product of a combination of telephone and radio transceiver (for more detailed information about these two technologies, see how the phone works and how it works). Cordless phones have two main parts: a landline and a handset. The landline is connected to the telephone jack via a standard telephone line connector. In the case of a telephone system, the landline is similar to an ordinary telephone. A landline receives incoming calls through telephone lines (in the form of electrical signals), converts them into FM radio signals, and then spreads the signals.
