Common radio terms explained

DC DC is the abbreviation of direct current. Generally ,
it refers to the current whose direction does not change with time. AC AC is the abbreviation of alternating current. Generally, it refers to the current whose magnitude and direction change periodically with time. Its basic form is sinusoidal current. The time required for AC to change once is called the cycle.

Form factor and crest factor
The form factor is a factor that indicates the sharpness of the periodic wave. It is the ratio of the effective value to the average value of the periodic wave. The crest factor is the ratio of the peak value to the effective value.

Voltage and electromotive force
Voltage is the potential difference between two points in a circuit, represented by the letter U. Electromotive force is the potential difference caused by the conversion of other energy into electrical energy.

Electric
current The regular flow of electric charges is called electric current.

Electric power
In an AC circuit, electric power is divided into active power, reactive power and apparent power (also called apparent power).

Radio
It is the abbreviation of radio holding technology.

Radio waves
refer to electromagnetic waves with a frequency range of about 3KHz~3000GHz, which are propagated in space using radio radiation or reception.

Wavelength
The distance that an electromagnetic wave travels during one cycle of oscillation is called its wavelength.

Frequency
The number of times or cycles that the direction of the current changes per second is called frequency.

Passband and cutoff frequency
In radio technology, the frequency range that various circuits, components, electronic devices and electroacoustic devices can be used in (generally defined as the frequency band within the range of 0.707 of the maximum current value) is called the passband. The upper and lower limit frequencies of the frequency band are called the cutoff frequencies.

Circuits and networks
The various devices that make up the current path and the power supply are called circuits. In a circuit, the circuits with the required electrical performance are connected by components and devices, which are called networks. Networks can be divided into two-terminal networks and four-terminal networks according to the number of external wire terminals; they can be divided into active and passive networks according to whether there is a power supply inside the network.

Equivalent circuit
For the convenience of calculation and analysis, under certain conditions, a circuit that can replace another circuit and an equivalent circuit with a given external performance is called an equivalent circuit.

Resistance and Conductivity
Resistance is the inherent property of a material that hinders the passage of electric current. The resistivity of a conductive material is represented by the letter ρ. The resistance of a conductor with a length of 1 meter and a cross-sectional area of ​​1 square millimeter at a certain temperature is usually called resistivity.

Effective resistance
It refers to the ratio of the power lost in an AC circuit to the square of the effective value of the current.

Reactance and Susceptance
The resistance and resistance of capacitor C and inductor L to AC is called reactance. Susceptance is the reciprocal of reactance.

Impedance and Admittance
In a circuit with resistance and reactance, the resistance and obstruction to sinusoidal alternating current is called impedance. Admittance is the guiding and accommodation effect of conductance and susceptance on sinusoidal alternating current.

Wave impedance
The ratio of the electric field strength to the magnetic field strength of an electromagnetic wave at any point in free space or in a waveguide is called wave impedance.

Characteristic impedance
It is one of the parameters of a uniform transmission line or a symmetrical passive four-terminal network. On an infinitely long uniform transmission line, the ratio of the complex voltage to the complex current at any point is equal, and their ratio is called characteristic impedance.

Impedance matching
is the measure by which a load obtains maximum energy from a network, transmission line or other device.

Level
It is a parameter that indicates the relative size of voltage, current or electric power.

Attenuation:
The phenomenon that electric energy gradually weakens over time or distance during transmission is called attenuation.

Gain
In electronic amplifiers, it represents the power amplification factor. It is usually expressed as the logarithm of the ratio of output power to input power.

Signal
When information is transmitted using electric current (voltage), radio waves, etc., the electric current (voltage), radio waves, etc. carrying information are called electrical signals (also referred to as signals for short), such as radio signals, television signals, and radar signals. Signals have three basic indicators: duration, bandwidth, and strength.

Noise
Also called noise. Sounds of different frequencies and intensities that are irregularly combined and sound noisy are called noise. In circuits, interference with a relatively wide frequency range caused by the continuous or impactful chaotic movement of electrons is called noise. In radio receiving equipment, all non-useful electrical signals are collectively called noise.

Signal-
to-noise ratio The ratio of signal to noise.

Sensitivity
refers to the sensitivity of a radio receiving device or electronic instrument to a tiny external signal.

Selectivity
The ability of a radio receiver or other electronic device to select the desired frequency from many frequencies is called selectivity.

Fidelity
Also known as "high fidelity". It is a measure of how closely the output signal of a radio electronic device can reproduce its input signal.

Distortion
The distortion of electronic amplifier circuits includes nonlinear distortion and linear distortion. Nonlinear distortion is also called harmonic distortion. It is caused by nonlinear elements and is manifested as the presence of some new harmonic components in the output signal that are not in the input signal. It is usually expressed as the percentage of the total RMS value of each harmonic in the output voltage and the RMS value of the pure sinusoidal output voltage.

Frequency response
It is one of the important indicators of radio electronic equipment, which refers to the change of gain (or loss) of radio amplification equipment or network with frequency.

Time constant
In radio technology, it generally refers to the rate of change of a circuit containing R, C or L parameters in response to an input signal, usually represented by the letter r.

Oscillation
The process in which the current (or voltage) in a circuit changes periodically and repeatedly between the maximum and minimum values ​​over time. After the external electromotive force is removed, the circuit can oscillate by relying on its own stored energy, which is called free (or natural) oscillation; the oscillation in which the amplitude of the current (or voltage) decreases over time is called damped oscillation or reduced amplitude oscillation; if the circuit is periodically supplied with appropriate energy to maintain the amplitude of the current domain (or voltage) constant, it is called constant amplitude oscillation. An electronic circuit that can generate oscillating current is called an oscillating circuit.

Tuning
The method of adjusting the oscillation frequency of the oscillation circuit to make it equal to the frequency of the external signal to achieve resonance is called tuning.

Quality factor
Also known as Q value. It is a quality indicator that characterizes the ratio of energy stored in an energy storage element (such as an inductor or capacitor) or an oscillating circuit to the energy lost per cycle, and is often represented by Q.

Modulation
The method of making certain parameters (such as amplitude, etc.) of the modulated signal (such as high-frequency electrical oscillation, etc.) change according to the changing rules of the modulating signal (such as audio signal, etc.) is called modulation.

Demodulation
It is the modulation and inverse process. That is, the method of reproducing the original modulated signal from the modulated wave process through the opposite process of modulation. The device that realizes the demodulation task is called a demodulator.

Coupling and decoupling
Coupling is also called "cross-coupling". The coupling phenomenon is the phenomenon that when two or more circuits form a network, the current or voltage of one of the circuits changes. Coupling circuits are divided into various forms such as resistance coupling, capacitance coupling, inductance coupling, resistance-capacitance coupling and mutual inductance (transformer) coupling. Among them, resistance-capacitance coupling and mutual inductance coupling are commonly used.

Feedback
Also known as "feedback". It refers to the process of returning part of the energy at the output end to the input end in an electronic circuit.