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NOT 516-2002-en

AMPLIFICATION OF ADJACENT CHANNELS USING A BROADBAND AMPLIFIER

Description: 

the output level of a broadband amplifier is a function of the number of input channels:

vout = vout.max. – 7,5 log (n – 1)

where:

v out is the expected output level.

vout.max.is the nominal output level of the broadband amplifier.

n is the number of channels.

this mathematical formula is not suitable for most of the installers.

in the technical information supplied by the manufacturers, this formula is converted into a table for direct application in the field.

in practice this v out has to be reduced when taking the following into account:

  • we must not force the amplifier to work at its nominal level vout.max. to avoid its saturation.
  • a reduction of 4 db in the output level is enough.
  • the state of all input channels coming into the broadband amplifier.

in other words, the calculations and measurements of the output level in the factory are made with perfect input signals.

in practice, this is not true, especially in cases as shown below, where channels that are being amplified come from modulators.

  • due to this, the output level has to be decreased at least another 5 db.

 

being:

  • fi (mhz) beginning of the considered tv channel
  • fi + 8 (mhz) end of the considered tv channel
  • fi - 8 (mhz) end of the preceding tv channel
  • fi + 16 (mhz) beginning of the next tv channel

the typical frequency response of a channel amplifier is:



typical frequency response of two adjacent channel amplifiers.

ch2 vestige could interfere with ch1 if its level were high enough.

typical frequency response of two non adjacent channel amplifiers (1 guard channel):

ch2 vestige cannot interfere with ch1 even if its level is high enough.

Id Anrterior: 
54
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