Knowledge base on EMC, Electrical safety and ce-test, qualified testing bv

 

 

 

 

 

 

 

 

Decade

A range of 1 - 10, or 100-1000, such as 1V - 10V or 1000-10000 Hz. Expressed logarithmatically  that is 20 dB.

Decibel (dB)

Logarithmic representation of a ratio measurement. Although it expresses the ratio of two power levels, it may be used for other (electrical) ratios. It is most commonly used for expressing power, voltage and current ratios as follows: Power Ratio dB = 10 log (P1/P2), Voltage Ratio dB = 20 log (V1/V2), Current Ratio dB = 20 log (I1/I2). Not that a factor 2 equals 6 dB for voltage and current and 3 dB for Power (approx).  The decibel is also commonly used for sound power levels although that must be dBpW officially (level above 1pW) . Referenced against 1 mW into 50 Ohms, the 0 dBm is a common referencr level in RF engineering.

dBm

Differential Mode Noise or -Interference

Interference characterises itself as differential mode (DM) when the sum of the interference currents (Idm) in all leads equals 0.  The difference is called Common Mode (if not zero). DM interference is not easy to be distinguished from signal current. The interference caused by DM currents is limited, as the fields from adjacent leads in a cable tends to cancel out.

Differential mode current

Dipole Antenna

Antenna of which the radiation properties are defined by physical dimensions close to half or a quaerter  of a wavelength. Radiation impedance at resonance is 50-73 Ohms for open dipoles, and 300 Ohms for folded dipoles.