Measurement Techniques, Test Equipment and Compliance Verification
This domain tests whether you can make a compliant measurement and defend the number: choosing the right instrument and detector, applying every correction, and reporting uncertainty honestly. Compliance results stand or fall on setup details.
Instruments
Spectrum analyzers and EMI receivers show amplitude against frequency; power meters measure true average power; signal generators, field-strength meters, near-field probes and line impedance stabilization networks support specific tests. Every instrument and antenna needs calibration traceable to a national standard, with correction factors applied for antenna factor, cable loss and attenuator value.
Spectrum analyzer mechanics
Reference level, resolution bandwidth, video bandwidth and detector set what you see. Reducing the resolution bandwidth by a factor of ten lowers the displayed noise floor by 10 dB but slows the sweep proportionally. Peak detection is fast and good for pre-scans; quasi-peak is used against CISPR limits; RMS or average detection is used for power density and average limits.
Compliance measurement
Conducted measurements at the antenna port use a known attenuator; radiated measurements use an open area test site or semi-anechoic chamber at 3 or 10 m, with the equipment rotated and cables moved. CISPR bandwidths are 9 kHz below 30 MHz, 120 kHz from 30 to 1000 MHz and 1 MHz above 1 GHz. Reported results must include measurement uncertainty.
Worked example
An analyzer reads -10 dBm while a 20 dB attenuator and 3 dB of cable loss sit between source and input. The source is -10 + 20 + 3 = +13 dBm. In a second case, a noise-like reading of -40 dBm at 100 kHz resolution bandwidth drops to -50 dBm when the bandwidth is narrowed to 10 kHz, while a continuous-wave carrier stays at its level. That difference is how you separate a real signal from the noise floor.
Traps that cost marks
Forgetting attenuator and cable corrections; applying a peak reading against an average limit; overdriving the input so the analyzer generates its own distortion; measuring in the near field; and assuming a preamplifier lowers the noise floor without raising distortion.