Phase-noise comparisons require more than one headline number. Record the carrier frequency, offset frequency, measurement method and operating conditions before comparing analyzers or signal sources.
What a spot phase-noise value means
Single-sideband phase noise is commonly expressed in dBc/Hz: noise power density relative to the carrier, normalized to a 1 Hz bandwidth. The offset is the frequency separation from that carrier.
For example, a hypothetical value of −106 dBc/Hz at a 10 kHz offset describes one point on a phase-noise curve. It does not, by itself, specify the analyzer’s measurement floor or the behavior at other offsets. The carrier frequency and test conditions are still needed.
Separate the device result from instrument limitations
A spectrum-based measurement can include contributions from the signal source and analyzer, and amplitude noise can affect interpretation. Dedicated phase-detector and cross-correlation methods address different measurement limitations. Choose a method with adequate sensitivity for the expected device performance.
Compare specified values with specified values, and identify typical results separately. Record the reference configuration, signal level, temperature conditions and relevant options. A result measured at one carrier frequency should not be ranked directly against another instrument’s result at a different carrier frequency.
Spot noise, integrated phase noise and jitter
A spot value describes noise density at one offset. Integrated phase noise covers a stated range of offsets. RMS timing jitter additionally depends on carrier frequency; when RMS phase deviation is expressed in radians, divide it by 2π times the carrier frequency to obtain RMS time deviation in seconds.
Keep the integration limits and treatment of discrete spurs with the result. Two jitter numbers using different integration ranges are not directly comparable. Choose those limits from the application’s requirements, rather than applying a universal narrowband or wideband rule.
Compare actual instrument configurations
Check the model’s manufacturer documentation and form factor before placing it in a comparison table. For example, the Rohde & Schwarz FSVR is a benchtop real-time spectrum analyzer; it should not be listed as an “FSVR PXIe Variant.” Avoid numerical rankings when the measurement conditions have not been matched.
For a modular test system, verify the required measurement software, instrument configuration and supported reference connections. Browse PXI platform equipment or RF test equipment with those requirements in hand.