User Manual

GOSSEN METRAWATT GMBH 17

4.7 Measurement of Gain and Attenuation

In communications engineering, gain or attenuation is almost

exclusively given as a logarithm of the ratio between a measured

voltage and a given reference voltage in dB. In recurrent net-

works, it is thereby possible to determine the total gain or atten-

uation in a simple manner by adding or subtracting the individual

values. The reference voltage is 0.775 V (1 mW for 600 Ω);

attenuation at this voltage is 0 dB.

For gain and attenuation measurement, proceed exactly as

described in chapter 4.3.1 for AC voltage measurement; the

measured values, however, are to be read off the dB scale.

The range – 15 ... + 6 dB shown on the scale corresponds to the

AC voltage range 1.5 V. In the case of the higher voltage mea-

suring ranges 5 V , 15 V , 50 V ..., 10 dB, 20 dB, 30 dB ...

are to be added to the value read; see the table in chapter 5

showing the voltage measuring ranges.

If a DC voltage is superposed on the AC voltage to be mea-

sured, this can be cancelled out by using a suitable capacitor,

which is to be series-connected to the measuring input.

The operating voltage of the series-

connected capacitor must be at least

of the same magnitude as the peak

value for the voltage applied. If there is

an additional error of 1% of the measured value, it can be calcu-

lated from the formula opposite.

In mentionned formula, R

is the internal resistance of the mea-

suring instrument in the selected measuring range

0,89

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MΩ

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⋅⋅

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µF⋅≈