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NOT 517-2002-en

USING DISTRIBUTION LINE AMPLIFIERS

Description: 
  • when using distribution line amplifiers it is very important to: equalise the headend output
  • control the input level to each amplification stage
  • control the output level of the amplifier

minimum input level to an amplifier

this value is mainly determined by the noise figure of the amplifier and the desired s/n (signal-to- noise) ratio at the output.

min. input level (db┬Á) = 1.8 (db┬Áv) + amplifier nf + 43

example:

televes ref. 5368

it features nf= 6 db;

therefore

min input level = 1.8 + 6 + 43 = 50.8 (db┬Á)

maximum input level to an amplifier

the maximum designed output voltage and the amplifier gain determines this value.

max. input level (db┬Áv) = vmax. - 7.5 log (n-1) - g

being:

n= no. of channels. this factor is given by the manufactures as a table where for each number n you will find the value 7.5log(n-1).

example:

televes ref. 5368

it features a max.output level for 2 channel =117 dbuv

therefore

max input level = 117 - 9.5 - 41 = 66.5 dbuv

in general every time the number of amplifiers is doubled, the minimum input voltage must be increased by three db's to overcome the extra amplifier noise;

similarly, the maximum input voltage must be reduced by 3 db to compensate for the increase in distortion levels.

in practice the input level to the distribution amplifier should be around 60 dbuv.

Id Anrterior: 
55
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