Microwave Tech - What is a high frequency circuit and how to distinguish between high frequency and low frequency

What is a high-frequency circuit?
To put it bluntly, high-frequency circuit boards are radio circuits, but they do not involve microwave circuit boards(microwaves are used to process circuits above one gigahertz, starting from the electromagnetic field of physics, which is very different from our common circuits), used for radio waves Transmit, receive, modulate, demodulate, amplify, etc.
What is a high-frequency circuit and how to distinguish between high frequency and low frequency?
In radio technology, 3-30MHz radio waves are called "high frequency". Due to the high frequency, in high-frequency circuits, the effects of signal transmission time, distributed inductance, and distributed capacitance must be considered. High-frequency circuits are basically composed of passive components, active devices, and passive networks. The frequency characteristics of components used in high-frequency circuits are different from those used in low-frequency circuits. Passive linear components in high-frequency circuits are mainly resistors, capacitors and inductors.
Application areas of high-frequency circuits
Application: high-frequency small-signal amplifier, high-frequency power amplifier, sine wave oscillator, amplitude modulation, detection and mixing, angle modulation and demodulation, and feedback control circuit. Wait a lot of fields.

What is the difference between high and low frequency?
1. PCB high-frequency board refers to radio waves with a frequency band from 3MHz to 30MHz. HF is mostly used for civil radio broadcasting and shortwave broadcasting. It has weak resistance to the radio waves emitted by electronic equipment, so it often interferes.

2. Low frequency refers to the lowest frequency range applied in a certain technical field. For example, in the radio band, frequencies in the range of 30 to 300 kilohertz are called low frequencies; in electronic amplifier circuits, frequencies close to audio (20 Hz to 20,000 Hz) are called low frequencies.
Generally refers to the frequency of 20HZ-160HZ. Among the sounds that can be heard by the human ear, the low frequency is the basis of the sound and the thickness of the sound.
Many fields involve "high frequency and low frequency", which refers to the level of frequency (frequency), but generally refers to various oscillations in physics. Among them, there are many oscillations in electricity, which may be electric current, mass point, electromagnetic field, etc. Vibration, "high and low frequency" is a description of vibration, and the results caused by high frequency and low frequency are also different.

In a circuit, inductance has different impedances for currents of different frequencies (in layman's terms, it is an obstacle), and capacitors have similar properties.
The general EQ division of BASS is: low-frequency system 50HZ to 300HZ, medium, and low frequency is 300HZ to 1250HZ, the intermediate frequency is 1250HZ to 3300HZ, medium and high frequency are 3300HZ to 6500HZ, and high frequency is above 6500HZ.

How to distinguish high and low frequencies

There is no LC frequency selection network in the low-frequency circuit, but there must be an LC frequency selection network in the high-frequency circuit. The low-frequency amplifier circuit works in Class A, all signals are amplified, and the high amplifier circuit works in Class C, but some of the signals are amplified. Frequency selection must be done through the frequency selection network