How do I perform a radiated emissions scan of an RF device for pre-compliance testing?
Radiated Emissions Pre-Compliance
Pre-compliance testing saves time and money by finding emissions problems before formal testing at an accredited lab ($3,000-10,000+ per test session). Fixing a problem after formal testing fails can cost weeks of delay and engineering time.
| Parameter | SOLT Cal | TRL Cal | eCal |
|---|---|---|---|
| Accuracy | Good | Excellent | Good-very good |
| Standards Needed | 4 (S,O,L,T) | 3 (T,R,L) | 1 (module) |
| Bandwidth | Broadband | Band-limited | Broadband |
| Setup Time | 5-10 min | 10-20 min | 1-2 min |
| Best For | Coaxial, general | On-wafer, waveguide | Production, speed |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
Frequently Asked Questions
What equipment do I need?
Minimum pre-compliance setup: spectrum analyzer: any spectrum analyzer covering 30 MHz-6 GHz. Cost: $3,000-20,000 (used instruments available for less). Set RBW to 120 kHz (for CISPR Band C/D) and 9 kHz (for Band A/B). Antennas: biconical (30-300 MHz, $200-500) + log-periodic (300 MHz-3 GHz, $300-700) or hybrid bilog ($500-1000). Antenna factors: calibration data from the antenna manufacturer (converts received voltage to field strength). Tripod and non-conductive table. Total cost: $5,000-25,000 for a basic pre-compliance setup.
How do I interpret the results?
Compare the measured emissions (in dBuV/m) to the regulatory limits: if all emissions are more than 6 dB below the limit (adequate margin): the device is likely to pass formal testing. If emissions are within 6 dB of the limit: the device may pass or fail depending on measurement uncertainty and the formal test environment. Take corrective action to add margin. If emissions exceed the limit: the device will likely fail formal testing. Identify the emission frequency and determine the source (clock harmonic, switching regulator, data bus, RF oscillator). Apply EMI mitigation: shielding, filtering, grounding, PCB layout changes. Common emission sources: clock harmonics (integer multiples of the system clock), switching regulator harmonics (at the switching frequency and harmonics), and unshielded cables acting as antennas.
What about conducted emissions?
Conducted emissions: measure the RF noise conducted from the device onto the AC power cord or other cables. These emissions must also comply with regulatory limits (CISPR 32, FCC Part 15). Measurement: use a LISN (Line Impedance Stabilization Network) between the AC power source and the DUT. The LISN provides a standardized impedance and routes the conducted noise to the spectrum analyzer. Frequency range: 150 kHz-30 MHz. Limits: FCC Part 15B Class B specifies maximum conducted emission levels. Conducted emissions testing is often done alongside radiated emissions for complete pre-compliance verification.