Is there a systematic explanation of radio knowledge on the Internet?

Electromagnetic wave (1) generation: When a rapidly changing electric current passes through a conductor, the conductor emits electromagnetic waves into the space around it.

2) Propagation: The propagation of electromagnetic waves does not require a medium, it can propagate in a vacuum, and it can also propagate in a medium. The electromagnetic waves used in radio communication are called radio waves, which are electromagnetic waves with a frequency within a certain range.

3) The relationship between frequency, wavelength and wave velocity: the speed of electromagnetic waves propagating in a vacuum is the same as the speed of light, and the speed of propagation in air is similar to that of a vacuum. The relationship between frequency, wavelength, and wave velocity is wave velocity = wavelength x frequency (or wave velocity = wavelength period), which is expressed by the letter as v = f (or v = t).

Band Application Band (Frequency Band) Symbol Wavelength Range Frequency Range Application Range Ultra Long Wave (VLF) VLF100000-10000M3-30kHz Coast: Submarine Communications.

Maritime Navigation Long-wave (low-frequency) LF10000-1000M30-300kHz medium-range communication in the atmosphere.

Underground rock formation communications.

Maritime Navigation Medium wave (MF) MF1000-100M300-3000KHZ broadcast.

Maritime Navigation Shortwave (HF) HF100-10M3-30MHZ long-distance shortwave communication.

Shortwave broadcasting: ultra-short wave (VHF) VHF10-1M30-300MHz ionospheric scattering communication (30-60MHz).

Meteor Remnant Communications (30-100MHz).

Artificial ionospheric communication (30-144MHz).

Communication with space vehicles (aircraft, missiles, satellites) inside and outside the atmosphere.

Intra-atmospheric television, radar, navigation, mobile communications, decimeter wave (UHF) tropospheric scattering communication (700-1000MHz).

Small capacity (8-12 channels) microwave relay communication (352-420MHz).

Medium capacity (120 channels) microwave relay communication (1700-2400MHz) cm wave (UHF) SHF10-1cm3-30GHz large capacity (2500 channels, 6000 channels) microwave relay communication (3600-4200MHz, 5850-8500MHz).

Digital. Satellite communications.

Waveguide Communications: Millimeter Wave (Very High Frequency) EHF10-1mm30-300GHz Communications, Radio, and Television When Entering the Atmosphere.

1) Radio waves are a means of information carrier, which is used to transmit sound signals and image signals.

2) Launch process (radio and television station completion).

3) Reception process (radio and TV set).

Classmates, I personally think that the aperture you asked is relative to the antenna. Antenna aperture refers to the ratio of the maximum size of the antenna array d to the working wavelength d when this system is called a small base system d when this system is called a large base system and brother also knows that you are going to ask about the short wave aspect:

13. In radio direction finding, an antenna array with a variety of apertures should be used, what is the aperture of the antenna array How is the aperture of the antenna array distinguished.

Answer: The ratio of the maximum diameter d of the antenna array to the wavelength of the operating frequency band, i.e., d

The more commonly used distinguishing criteria are: d >1 is a wide aperture; d 《 for narrow apertures.

I understand the concept of aperture as the antenna array that receives the signal. For phased array antennas, the entire array can be an aperture, but in space-time adaptive processing, in order to improve the real-time performance of the algorithm, the entire array is often divided into several sub-arrays, and sometimes each sub-array is called a sub-aperture. The processing of each sub-aperture is relatively independent, that is, the processing process of each sub-aperture can be called a channel.

Of course, the concept of aperture is also often used in synthetic aperture radar to represent the equivalent array for each imaging process. Aperture is a physical concept of antenna, which can be an actual antenna array or a virtual one. When an antenna (such as phased array, DBF, etc.) functionally has multiple channels, then the antenna can be understood as having multiple sub-apertures; In the case of SAR or other integrated aperture radars, a moving antenna or multiple sparsely arranged antennas together form a single aperture.

The main contents of the Radio Fundamentals (Fourth Edition) are:

Wireless communication system composition and signal transmission, tuning amplifiers and filters, modulation and demodulation circuit applications, and installation and commissioning of FM AM radios.

Answer 1: It is difficult to answer this question specifically, the higher the frequency of the radio wave, the stronger the penetration, the worse the diffraction ability, the greater the attenuation, and the lower the frequency, the opposite. In fact, the penetration of microwave frequency is very strong, and the theoretical definition of microwave frequency band is 300MHz-3000GHz, which is generally believed to be more than 3GHz by industry insiders.

In some cases, the lower the frequency, the better, because of the diffraction ability of radio waves, if the building has a window it will diffract in, just from the wall of the building to penetrate in, that is the microwave band, and the higher the frequency, the better, but there is the problem of attenuation, the distance is doubled and the signal attenuation is 6db, then the higher the frequency, the closer the distance.

Answer 3: It has been explained in answer 1 that the 4G frequency is higher than the 3G frequency, so the penetration is also better, but the premise is that the distance is close enough. In my own words, network optimization is based on the use of geographic segmentation, which can achieve frequency multiplexing between cells with appropriate spacing, that is, to find a balance between signal transmission quality and signal interference.

Radio signals with high frequencies have more serious long-distance transmission losses under the same transmission conditions Network optimization 4G is much more troublesome than 3G Whether the wall can be transmitted is not determined by its own frequency alone There are too many interference factors Network optimization knowledge is a general term Including a lot of parameters collected through the monitoring of the entire network, such as: level value, voice quality value, MOS value, etc., the parameters, process, signaling, engineering parameters and other aspects are adjusted, so that the entire network work is in the best operation state.

The main contents of "Radio Fundamentals (Fourth Edition)" are: wireless communication system composition and signal transmission, tuning amplifiers and filters, modem circuit applications, and FM AM radio installation and commissioning. "Radio Fundamentals (4th Edition)" was compiled by Tang Xianglin, Liang Weiwen and Cheng Li, edited by Tang Xianglin, and edited by Liang Weiwen and Zhang Zhilin. Reviewed by He Peisen.