The difference between a TV transmitter and a radio receiver works in the same way, the former having an audio signal. Radio and television developed with the foundation of electronic technology. In 1906, people used the wireless application to congratulate the people on Christmas, but this technology has been delayed for ten years to achieve practical purposes. In 1916, Sarnov, the United States, drafted a plan to receive music broadcasts from radio stations. This is the world's first radio station. After the radio broadcasts were continuously improved in 1935, it was basically perfect. At that time, there were 1,550 radio stations in the world.
Programs that use radio waves or wires to transmit sound and images to a wide area are collectively referred to as "broadcasts." The radio radio can be divided into a tube radio, a semiconductor radio, and a solid-state radio according to the structure; it can be divided into a floor type, a desktop type, a portable type, a pocket type, and a miniature type according to the volume; and can be divided into a medium wave, a medium short wave, a short wave, an ultra short wave according to the band, Long, medium and short wave, full band; according to the broadcast system can be divided into amplitude modulation, frequency modulation; according to the program specifications can be divided into special and first, second, third, and fourth; according to the use of power can be divided into AC, DC, AC and DC use.
According to special and multi-purpose, it can be divided into automobile use, amplitude modulation, transfer, frequency transfer, transfer, sound, record, dual use, and other multi-purpose. Regardless of how complex or difficult the radio receiver is, it consists of four basic parts. This is very useful for us to understand the radio principle. These four parts: antenna, ground system: it receives radio waves, and then reproduces the currents of various frequencies. Tuner: It selects the current of a station that needs to be supplied, and suppresses the current of those stations that are not needed.
What is the difference between a TV transmitter and a radio receiver?
Detector: It changes the current of the desired station to a useful form of speaker that can be converted into sound: the current from the detector is converted into a sound that can be heard by the human ear. These four parts must exist for all kinds of receivers, whether it is the simplest ore radio or a complex TV receiver, but the latter has been improved. The radio is able to distinguish between individual stations and the choice of different carrier frequencies. The transmitter synthesizes the signal synthesized by the carrier and the audio signal, that is, the amplitude modulation or frequency modulation wave is transmitted to various directions, and the electromagnetic wave that oscillates rapidly is composed of an electric field and a magnetic field.
The electrons in the radio antenna move with the electric field vibration of all the radio signals arriving at the antenna. This tiny current is only equivalent to the current caused by a few microvolts. The "tuner" of the radio uses a resonant circuit that is tuned to the carrier frequency of a station you want to receive. Other carrier signals are suppressed because they are not resonant. The amplifier of the radio amplifies the resonant signal. The carrier frequency is separated from the voice signal by the detector circuit, and the audio signal is amplified again to restore the music and voice experienced by the adult ear from the speaker.
The number of radios is as much as 700 million. It is also mixed with the video signal. The TV has a part of the radio, and the TV also has a display circuit display corresponding to the video, a picture tube. The basic structure and working principle of the superheterodyne receiver can be started by the antenna first. Suppose there is a 800 kHz radio signal coming in from the antenna. After high frequency amplification, the signal is enhanced and the enhanced signal is sent to the mixer. The oscillator of the receiver itself also sends a signal to the mixer, which should have a frequency of 1,250 kHz.
The two electrical signals are mixed in the mixer to form a "beat", resulting in a new signal having a frequency of 1,250, minus eight hundred equals four hundred and fifty-five kilohertz. The frequency of 455 dry Hertz is called "intermediate frequency". In radio technology, it is called "intermediate frequency". If the frequency of the electrical signal transmitted by the antenna is 900 kHz, then the receiver itself must generate dry Hertz. Electrical signal. After being fed into the mixer, the mixed beat still yields an intermediate frequency signal of 1355 minus 900 equal to four hundred and fifty-five kilohertz.
The intermediate frequency electrical signal is amplified in a dedicated medium wave amplifier, and after the demodulated detector, the audio signal can be restored. The audio signal is also called the low frequency signal. After the audio signal is amplified again by the low frequency amplifier, the current can be sent to the speaker to make a sound.