Meaning
Measurement of the phase noise power in a one-hertz bandwidth on one side of the carrier signal defines the single-sideband distribution of frequency fluctuations. This single sideband noise is normalized to the carrier power and is used to characterize the spectral purity of an RF oscillator. The metric provides a way to evaluate how much noise a transmitter will emit into adjacent channels.
It is distinct from double-sideband measurements, which combine the noise from both sides of the carrier.
Measurement Standard
Expressing this metric involves measuring the power in a one-hertz bandwidth at a specified offset frequency from the carrier. The offset is chosen based on the channel spacing of the target communication system. For example, a system might specify a noise level of minus one hundred decibels relative to the carrier per hertz at a ten kilohertz offset.
Noise Origin
Theoretical models of oscillator noise show that the noise on each side of the carrier is symmetrical for most frequency-generation circuits. This symmetry allows designers to focus on a single sideband when evaluating the system’s noise performance. Flicker noise dominates at small offsets, while thermal noise dominates at larger offsets.
Receiver Sensitivity
High levels of this single-sided noise can result in desensitization of adjacent channel receivers. When a transmitter emits high levels of out-of-band noise, it raises the noise floor of nearby receivers. This interference reduces the effective range and data rate of the communication system.
