Signal bandwidth: A signal can be decomposed into a weighted sum of a series of sine and cosine functions of different frequencies. Bandwidth is the frequency width of the trigonometric function corresponding to the weighted non zero portion. The width of the signal spectrum, which is the difference between the highest frequency weight and the lowest frequency weight of the signal. For example, a square wave signal composed of several sine waves has a minimum frequency weight of its fundamental frequency, assuming f=2kHz, and a maximum frequency weight of its 7th harmonic frequency, that is, 7f=7 × 2=14kHz, so the signal bandwidth is 7f – f=14-2=12kHz. In computer networks, bandwidth is used to indicate the ability of a channel in the network to transmit data. Therefore, network bandwidth indicates the “highest data rate” that a channel in the network can pass through per unit time.
Channel Bandwidth: Constrains the lower and upper frequency limits of the signal allowed to pass through the channel, which means constraining a frequency passband. For example, the allowable passband for a channel is 1.5 kHz to 15 kHz, with a bandwidth of 13.5 kHz.
How to judge whether a signal can pass through a channel: The lowest and highest frequency weights of any composite signal can pass through the channel within the frequency range of the channel. For example, the allowable passband for a channel is 1.5 kHz to 15 kHz, with a bandwidth of 13.5 kHz. Frequencies of 1.5kHz, 4kHz, 6kHz, 9kHz, 12kHz, 15kHz, and any single frequency wave within the frequency band range can also pass through this channel. However, assuming a square wave with a fundamental frequency of 1 kHz, the distortion must be severe through this channel; If the fundamental frequency of a square wave signal is 2kHz, but the highest harmonic frequency is 18kHz, and the bandwidth exceeds the channel bandwidth, its 9th harmonic will be filtered out by the channel, and the square wave received through the channel does not have good transmission quality; So, if the fundamental frequency of a square wave signal is 500 Hz and the maximum frequency weight is 11 harmonics, the frequency is 5.5 kHz, and its bandwidth only needs 5 kHz, which is much smaller than the channel bandwidth, can it pass through the channel well? In fact, when the signal is transmitted over the channel, the fundamental frequency is filtered out, and only harmonics can pass through. The signal waveform must be unsightly.
