Spurious tone

In electronics (particularly radio systems), a spurious tone (also known as an interfering tone, a continuous tone or a spur) is an unwanted signal component at a discrete frequency that interferes with a desired signal.^[1]

Spurious tones may arise within an electronic circuit and can appear alongside the desired signal. They also include tones generated within back-to-back connected transmit and receive terminals or channel units, when the fundamental is applied to the transmit terminal or channel-unit input.^[1]

Spurious tones are typically generated by imperfections in electronic systems, including:

• Nonlinearities in amplifiers and mixers
• Imperfections in oscillators and frequency synthesisers
• Leakage or unintended coupling between signal paths^[2]

Such effects can give rise to unwanted signals, including harmonics and intermodulation products.^[2]

Spurious tones are analysed in the frequency domain using instruments such as spectrum analyzers. Their amplitude is commonly expressed relative to the main signal, for example in decibels relative to the carrier (dBc).^[2]

A related performance metric is the spurious-free dynamic range (SFDR), which describes the ratio between the fundamental signal and the largest spurious component within a specified bandwidth.^[3]

Spurious tones can degrade system performance by introducing interference, reducing signal-to-noise ratio, and causing distortion in communication systems.^[2]

• Harmonic
• Intermodulation
• Phase noise
• Spurious-free dynamic range

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