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Contents

1 Levels 3

2 Formulas 5

3 Conversion from the Power Level to the Voltage Level and Vice Versa 7

Appendix

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1 LevelsThe Absolute Level

The absolute level is a logarithmic value which shows the difference between themeasured value and the reference value.

Reference Values (relative point zero)

Resistance: R = 600 9(nominal resistance of a VF telephone line)

Power: P = 1 mW

(power of a microphone when "a" is spoken aloud)

Voltage: V = 0.775 V

P = V2 / R ; V = PxR mWx= 1 600W = 0,775 V

Current: I = 1.29 mA

P = I2xR ; = PxR mWx= 1 600W = 1.29 mA

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2 FormulasAbsolute power level:

nPabs = lg (Pm/1 mW) [B]

nPabs = 10 lg (Pm/1 mW) [dBm]

B=Bel; Pm = measured power

Absolute voltage level:

nUabs = 20 lg (Um/0.775 V) [dBu]

10 lg (Pm/1 mW) = 10 lg ((Um2x600 9) (0.7752V2xRm))

20 lg (Um/0.775 V) + 10 lg (600 9/Rm)

Absolute current level:

nlabs = 20 lg (lm/1.29 mA) [dBi]

10 lg (Pm/1 mW) = 10 lg ((lm2xRm) / (1.292 mA2x600 9)) =

20 lg (lm/1.29 mA) + 10 lg (Rm/600 9)

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3 Conversion from the Power Level to theVoltage Level and Vice Versa

10 lg (Pm/1 mW) = 20 lg (Vm/0.775 V) + 10 lg (600 9/Rm)

absolute absolute correction

power level voltage level factor level

TIP

With a resistance of 600 9, the absolute levels of voltage, current and power havethe same value - if the recommended standard values are used!

In the field, the absolute power level and the absolute voltage level are used fortelecommunication path measurements.

The absolute power level may be calculated with the voltage level and the levelcorrection factor according to the above formula.

Important level correction factors ncor:

Rm [9] ncor [dB]

3000 -6.989

2400 -6.0206

600 0 = 0

250 3.82

150 6.0206 = 6

75 9.0309 = 9

50 10.79

35 12.43

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dB level relation (e.g. attenuation or gain)

dBr relative levelreferred to the zero relative level point,

dBm absolute power level, referred to 1 mW

dBu/dBv absolute voltage level, referred to 0.775 V

dBm0 absolute power levelreferred to the relative level (dBr),relation: dBm0 = dBm - dBr

dBm = dBr + dBm0

dBv0 absolute voltage level

referred to the relative level (dBr),relation: dBv0 = dBv - dBr dBv = dBr + dBv0

dBmp absolute (noise) power level, referred to 1 mWand CCITT weighted,

weighted = ponderedi.e. measured with a psophometer, A-filter

dBm0p absolute (noise) power level,referred to the relative level and CCITT weightedrelation: dBm0p = dBmp - dBr

dBmp = dBr + dBm0pdBrnc absolute noise level, "C-characteristic" weighted,

reference noise c-characteristic weighting

dBa absolute noise level, "FIA-characteristic" weighted,adjusted weighting acc. to FIA characteristic

dBV absolute peak-to-peak voltage levelfor TV signal measurements

relation: OdBV = 1 V pp/75 9

= 2.2 dBm/75 9

= -6.8 dBv/75 9

dBvs absolute voltage level in the sound channel,referred to 0.775 V

dBvps absolute (noise) voltage level in the sound channelreferred to 0.775 V and CCITT weighted

dBv0ps absolute (noise) voltage level in the sound channel,referred to the relative level (dBr)and CCITT weighted.