EMI receiver vs spectrum analyzer: what is the difference?
Differences between an EMI receiver and a spectrum analyzer (detectors, bandwidth, overload tolerance, preselector) and cautions when using an analyzer for pre-compliance.
Both show signals in the frequency domain, but the instrument designed for standards testing is the EMI receiver. A spectrum analyzer with correct settings and protection is still good enough for pre-compliance work.
Main differences
| Item | EMI receiver | Spectrum analyzer |
|---|---|---|
| Detectors | Peak, quasi-peak, average as the standard defines | Some models only; quasi-peak often needs an option |
| Resolution bandwidth | Standard-specified values (for example 120 kHz) and filter shape | Freely settable, but filter shape may differ |
| Overload tolerance | Preselector and input protection tolerate strong signals | Strong signals can create intermodulation distortion |
| Sensitivity / noise | Usually includes preamp and filters | An external preamp is often required |
| Use | Certification testing | Pre-compliance, debugging |
When using an analyzer for pre-compliance
- Set the resolution bandwidth to the standard value and use a quasi-peak detector if available. Otherwise look at peak first and check only the frequencies near the limit separately.
- In strong-signal environments add attenuation and place a filter before the preamp to avoid overload.
- Sweeping too fast misses intermittent signals. Check that the dwell time is long enough (calculator: scan time).
- Confirm the instrument noise floor is well below the limit. If the noise is near the limit, the margin cannot be known accurately (calculator: noise floor).
Analyzer results can differ from certification results by several dB. Verify items with small margin at a formal test lab.
Field notes
- In one case a product passed pre-compliance but exceeded the limit in the formal test. The cause was internal heating. The pre-compliance measurement was taken right after switching the product on, while the formal test was taken after a 30-minute warm-up. We concluded that the heat changed the values of internal parts (for example resistors) and shifted the result.
- Measuring pre-compliance after the same stabilization time as the formal test reduces this kind of difference.
Related calculators
Results and summaries are for reference. For certification and test reports use the latest official standard text and calibrated instrument data.