What time is it on the radio? What channel does Xiaomi and boss Artu tell jokes on?

* The earliest form of sound broadcasting was wireless telegraph at sea. It uses a switch to control whether to emit continuous waves, so as to generate intermittent sound signals at the receiving end, that is, Morse code.

* AM broadcasting can spread music and sound. AM broadcasting adopts amplitude modulation technology, that is, the greater the volume received by the microphone, the greater the energy emitted by the radio station. This signal is susceptible to interference such as lightning or other interference sources.

* Compared with AM broadcasting, FM broadcasting can spread music and sound with higher fidelity. For frequency modulation, the greater the volume received by the microphone, the higher the frequency of the transmitted signal. FM broadcasting works at a very high frequency (VHF). The higher the frequency band, the wider the frequency bandwidth it has, so it can accommodate more radio stations. At the same time, the shorter the wavelength, the closer the propagation of radio waves is to the linear propagation of light waves.

* The sideband of FM broadcasting can be used to spread digital signals, such as logo, program name introduction, website, stock market information, etc. In some countries, FM radio can automatically find the original channel according to the sideband information after moving to a new area.

VHF AM technology is applied to voice stations used in navigation and aviation. This makes it possible to use light antennas on airplanes and ships.

* Government, fire fighting, police and commercial radio stations usually use narrowband FM technology on dedicated frequency bands. These applications usually use a bandwidth of 5KHz. Compared with the 16KHz bandwidth of FM radio or TV sound, fidelity is sacrificed.

:: Civil or military high-frequency voice services use short waves to communicate between ships, planes or isolated locations. In most cases, single sideband technology is used, which can save half of the frequency band and use the transmission power more effectively compared with amplitude modulation technology.

* Terrestial Trunked Radio (TETRA) is a digital trunked telephone system designed for special departments such as military, police and first aid.

telephone

* Mobile phone or mobile phone is the most widely used wireless communication method at present. The coverage area of a cellular phone is usually divided into multiple cells. Each cell is covered by a base station transmitter. Theoretically, the shape of the cell phone battery is a honeycomb hexagon, which is also the source of the cell phone name. At present, the widely used mobile phone system standards include GSM, CDMA and TDMA. Operators have started to provide the next generation 3G mobile communication services, and the leading standards are UMTS and CDMA2000.

* There are two types of satellite phones: Inmarsat and Iridium system. Both systems provide global coverage services. INMARSAT uses geosynchronous satellites and needs directional high-gain antennas. Iridium is a low-orbit satellite system, which directly uses mobile phone antenna.

TV

* Usually, analog TV signals are transmitted in the same signal through amplitude modulation, audio modulation and synthesis.

* Digital TV adopts MPEG-2 image compression technology, which only needs about half the bandwidth of analog TV signal.

Emergency radio communication service

* Emergency position indicating radio beacon, emergency positioning transmitter or personal positioning beacon is a small radio transmitter, which is used for positioning or measuring by satellite in an emergency. Its function is to provide rescuers with the exact location of the target, so as to provide timely rescue.

data transmission

* Digital microwave transmission equipment, satellites, etc. Quadrature amplitude modulation (QAM) is usually used. QAM modulation uses the amplitude and phase of the signal to load information. In this way, more data can be transmitted on the same bandwidth.

* IEEE 802. 1 1 is the current WLAN standard. Using 2GHz or 5GHz frequency band, the data transmission rate is 1 1 Mbps or 54 Mbps.

* Bluetooth is a short-range wireless communication technology.

identify

* Active and passive radios can be used to identify and indicate the identity of objects. (See Radio Frequency Identification)

other

* Amateur radio is radio communication in which radio enthusiasts participate. Amateur radio stations can use many open frequency bands in the whole spectrum. Fans use different coding methods and techniques. Some later commercial technologies, such as frequency modulation, single sideband amplitude modulation, digital packet radio and satellite signal transponder, were first applied by amateurs.