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NOT 604-2002-en

HOW TO MEASURE THE CARRIER-TO-NOISE RATIO AT THE OUTPUT OF AN AMPLIFIER

Description: 

Equipment required:

Spectrum analyzer (SA)

Method of measurement:

Connect the antenna to the input of the amplifier and power it.

Connect the SA to the output.

Set the equipment controls so as to be able to see the channel(s) that are to be tested.

First of all, set the SA as follows:

  • IF filter bandwidth to 1 MHz (better if it is set to 3 MHz).
  • Video filter bandwidth: set it to the maximum value.
  • Then measure the level of the chosen TV channel video carrier.

Record this measured value: C output.

Now select a portion of the output band with only noise, and set new SA parameters:

  • IF filter bandwidth: 1 MHz.
  • Video filter bandwidth: set it to the minimum value.
  • Measure the noise level and record it : N output.
  • We now need to make a slight correction due to the different bandwidth (5MHz) of the TV settings.

This value will be: 10 log 5/1= 7 dB.

  • Subtract this value (7 dB) from the measured noise level. Noutput

This is the real noise level N output carrier = (N output - 7) dB.

Finally, calculate the C/N by subtracting this value from the value recorded previously:

C/N output = C output - N output carrier = C output - N output - 7 dB.

Id Anrterior: 
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