Appendix D.- Carrier To Noise Ratio (C/N); Analogue Channels - Promax 10 Manuel D'utilisation

APPENDIX D.- CARRIER TO NOISE RATIO (C/N)

-ANALOGUE CHANNELS-

The Carrier to Noise ratio is a signal quality measurement. The noise power
depends on the measurement filter bandwidth, in analogue TV it is usual to refer the
noise level to a bandwidth of 5 MHz (this is the case of the PROMAX-10). If it is desired
to know the C/N measurement for a different bandwidth (BWx), the following correction
should be applied.
Starting from the C/N definition:
where C:
N :
BWX
and as the noise power referred to BWx could be related with the noise power referred
to 5 MHz according to:
the C/N ratio referred to a noise measurement bandwidth BWx should be expressed as:
= −
C / N C N
BW BW
X X
That is to say, the factor 10 log (BWx / 5 MHz) should be subtracted to the
PROMAX-10 readout.
There exist some standards that determine the minimum C/N value for an
installation. In general, greater values than 40 dB are considered as good quality
signals. Under 40 dB snow should appear on the TV screen.
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=
C / N C
BW
X
Video carrier level
Noise power referred to a BWx measurement bandwidth
= +
N N
BW 5 MHz
X
= − −
C N 10 log(
5 MHz
5
USER'S MANUAL. PROMAX-10
−
N
BW
X
BW
X
10 log( )
5 MHz
BWx
=
) C / N
−
PROMAX
MHz
BWx
−
10 log( )
10
5 mhZ
04/2004