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0467-2013

Interpretation of the characteristic of "maximum output level" for a broadband amplifier, when it receives several COFDM channels (Area Switch-off) at its input.

Respuesta: 

The maximum output level of an amplifier indicates the maximum level that can be obtained at the output of the device ensuring linear operation, without introducing significant distortion to the input signal.
The linearity of an active element, such as an amplifier depends on the type and number of signals at its input, and varies depending on the type of modulation.
In general, the maximum output level indicated in the characteristics of an amplifier is measured according to the DIN 45004B (EN 50083) standard which expresses the maximum output level for 2 analog channels of equal amplitude at its input.

 


If the input signals are COFDM all of them, the maximum output level has to be reduced by 2 dB compared to the level obtained by applying DIN 45004B.
On the other hand, by increasing the number of channels at the input of a broadband amplifier, its maximum output level has to be reduced by an amount given by the formula:

 

     V salida máxima = 7,5log(N-1)

where "N" represents the number of channels.
Therefore, the maximum output level of a broadband amplifier for N COFDM channesl is the result of applying the following formula:

              Vo max (dB) =
V DIN45004B – 7,5 log (N-1) – 2 dB

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