Calculator Inputs
Example Data Table
These example values show how emissions and margins are derived across several frequencies.
| Freq (MHz) | Reading (dBµV) | AF (dB/m) | Cable (dB) | Preamp (dB) | Limit (dBµV/m) |
|---|---|---|---|---|---|
| 30.000 | 40.50 | 12.00 | 2.20 | 20.00 | 50.00 |
| 100.000 | 45.10 | 18.50 | 3.00 | 20.00 | 54.00 |
| 300.000 | 47.80 | 22.00 | 3.50 | 20.00 | 60.00 |
Formula Used
This calculator works with common radiated or conducted emission reporting in logarithmic units. It converts receiver readings to final emission level and then computes compliance margin.
- Emission level: E = Reading + AF + Cable − Preamp + Dcorr
- Distance correction: Dcorr = 20·log10(d_meas / d_limit)
- Margin: Margin = Limit − E
If Margin is positive, the emission is below the limit. If Margin is negative, the limit is exceeded at that point.
How to Use This Calculator
- Select Single point for one frequency, or Batch table for multiple rows.
- Enter distances to apply optional distance correction automatically.
- Fill receiver reading, correction factors, and the applicable limit.
- Press Submit to view results below the header.
- Use Download CSV or Download PDF to save the report.
FAQs
1) What is EMI margin?
EMI margin is the difference between the compliance limit and the calculated emission level. It quantifies headroom. Positive margin indicates passing. Negative margin indicates the emission exceeds the limit at that frequency.
2) Why are values in dB units added and subtracted?
Many EMC quantities use logarithmic units. Antenna factor and cable loss are corrections added to a receiver reading. Preamplifier gain is subtracted because it increased the receiver reading during measurement.
3) When should I use distance correction?
Use distance correction when your measurement distance differs from the distance stated in the limit line. The calculator applies 20·log10(d_meas/d_limit), which is a common far-field scaling approximation for radiated emissions.
4) Does a higher antenna factor always increase emission?
Yes. Antenna factor converts field strength at the antenna to the voltage at the receiver. A larger antenna factor raises the calculated field strength, increasing the emission level and reducing margin.
5) What if I do not use a preamplifier?
Set preamp gain to 0 dB. The emission formula will then only add reading, antenna factor, cable loss, and any distance correction. This keeps the result consistent with a direct receiver measurement chain.
6) How many batch rows can I paste?
You can paste many lines, but keep it reasonable for browser and server limits. Each line must contain six numeric values. If a row has a nonnumeric value, the calculator will stop and show the first error.
7) Why does the PDF look plain?
The PDF is generated without external libraries for easy hosting. It is designed for clarity and compatibility, using monospaced text. For branded reports, you can export CSV and format it elsewhere.
8) Can I use this for conducted emissions too?
Yes, if your corrections match the conducted measurement chain. Replace antenna factor with the correct transducer factor or LISN conversion, and keep units consistent. The margin concept remains Limit minus Emission.