Technical data
Table Of Contents
- EMC Measurement Application Measurement Guide
- Table of Contents
- 1 EMC Measurements
- 2 Conducted Emissions Measurements
- 3 Radiated Emissions Measurements
- A: Line Impedance Stabilization Networks (LISN)
- B: Antenna Factors
- C: Basic Electrical Relationships
- D: Detectors Used in EMI Measurements
- Glossary of Acronyms and Definitions
33
Basic Electrical Relationships
C: Basic Electrical Relationships
The decibel is used extensively in electromagnetic measurements. It is the log of the
ratio of two amplitudes. The amplitudes are in power, voltage, amps, electric field units
and magnetic field units.
decibel = dB = 10 log (P
2
/P
1
)
Data is sometimes expressed in volts or field strength units. In this case, replace
P with V2/R.
If the impedances are equal, the equation becomes:
dB = 20 log (V
2
/V
1
)
A unit of measure used in EMI measurements is dBμV or dBìA. The relationship of
dBμV and dBm is as follows:
dBμV = 107 + P
dBm
This is true for an impedance of 50Ω.
Wave length (l) is determined using the following relationship:
λ = 3x10
8
/f (Hz) or λ = 300/f (MHz)