Explanation of basic radio communication terms

Date:Jan 23, 2021

Many new HAMs are not very familiar with the terms of radio communication, and misoperation may occur in daily communication. We summarize the commonly used and basic radio communication terms for everyone to understand.

Audio: also known as audio frequency, which is the frequency that the human ear can hear. Usually refers to the frequency between 15 Hz and 20 000 Hz.

Voice frequency: refers to the language frequency within the audio range. In general telephone channels, it usually refers to a frequency between 300 Hz and 3 400 Hz.

Radio frequency: The frequency at which a radio transmitter can effectively transmit electromagnetic waves to space through an antenna, collectively referred to as radio frequency. If the frequency is too low, the effectiveness of the transmission will be reduced, so it is customary to call frequencies above 100kHz as radio frequency.

Video: The frequency range contained in television signals ranges from tens of hertz to several megahertz, and video is the general term for this frequency.

Carrier: A sine wave or periodic pulse that carries information, called carrier (or carrier frequency). With the change of the signal wave, the amplitude, frequency or phase of the carrier changes accordingly.

Signal: The amount of electricity used to express or carry information.

Channel: A channel divided according to the characteristics of the transmission of information. Including possible but not yet realized pathways.

Analog signal: A signal that is continuous in time or can take infinite values for a certain parameter.

Digital signal: The so-called digital signal refers to a discrete, discontinuous signal. The digital signal can only change and take values in a limited number of steps or increments. In other words, for digital signals, you only need to calculate the number of steps without considering the size of the signal within the steps (the most commonly used is binary encoding).

Band: In radio technology, the word band has two meanings. One refers to the division of electromagnetic wave spectrum, such as long wave, short wave, ultrashort wave and other wave bands. The second refers to the division of the working frequency range of transmitters, receivers and other equipment. If the operating frequency range is divided into several parts, these parts are also called bands, such as three-band radios.

Channel: The passband occupied by communication equipment is called channel. Usually a communication device has many channels in the frequency range it has.

Pass Band: The frequency range of a circuit that allows the current to pass smoothly is called the pass band of the circuit. It is generally stipulated that the width between two frequencies where the current is equal to about 0.707 times the maximum current value is the passband.

Frequency coverage: The frequency range in which communication equipment works is called frequency coverage. The ratio of the highest operating frequency to the lowest operating frequency is called the frequency coverage factor.

Cut-off frequency: a special frequency used to describe the frequency characteristics of the circuit. When keeping the amplitude of the circuit input signal unchanged, changing the frequency to reduce the output signal to 0.707 times the maximum value, or a special rated value, the frequency is called the cutoff frequency. There is a cut-off frequency at the high-frequency end and the low-frequency end, respectively called the upper cut-off frequency and the lower cut-off frequency. The frequency range between the two cutoff frequencies is called the passband.

Frequency stability: The frequency generated by the oscillator changes due to various reasons. The ratio of the magnitude of this frequency change to the rated frequency is called frequency stability. It is an important indicator to measure the quality of a communication system. To improve frequency stability, parameter frequency stabilization, crystal frequency stabilization and frequency synthesis are often used.

Allowable limit of residual wave radiation power: refers to the minimum allowable value of any residual wave radiation power generated by harmonic radiation, parasitic radiation and intermodulation other than fundamental wave radiation, in dB (decibel) or mW (milliwatts), μW ( Microwatts).

Bandwidth: Sometimes called the necessary bandwidth. Refers to the allowable value of the frequency bandwidth occupied in order to ensure the rate and quality of a certain transmitted information, expressed in hertz (Hz), kilohertz (kHz), and megahertz (MHz).

Selectivity: The ability of a radio receiver to select the signal of a desired station from many different frequencies is called selectivity. The better the selectivity of the receiver, the less susceptible to interference from other stations. Therefore, selectivity is one of the important parameters that determine the quality of the receiver.

Sensitivity: The ability of a radio receiver to receive weak signals is called sensitivity. If a receiver can receive a very weak signal, the sensitivity of the receiver is high, otherwise the sensitivity is low. Therefore, sensitivity is also one of the important parameters that determine the quality of the receiver.

Fidelity: also called fidelity. Refers to the degree of similarity between the output signal of the receiver and the input signal, that is, whether the receiver can amplify each frequency in the signal equally and restore it without distortion. For example, the better the fidelity of a radio receiver, the more realistic the language and music it outputs.