Appendix D.- Carrier To Noise Ratio (C/N); Analogue Channels - Promax 8 plus Manual Del Usuario Y Operador

APPENDIX D.-
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-8+). 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
That is to say, the factor 10 log (BWx / 5 MHz) should be subtracted to the
PROMAX-8+ 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.
Page 44
CARRIER TO NOISE RATIO (C/N)

-ANALOGUE CHANNELS-

C / N
BW
Video carrier level
Noise power referred to a BWx measurement bandwidth
=
N N
BW 5 MHz
X
= − −
C N 10
5 MHz
X
INSTRUCTION MANUEL. PROMAX-8+
= −
C N
BW
X X
BW
+ X
10 log( )
5 MHz
BWx
=
log( ) C / N
PROMAX
5 MHz
BWx
−
10 log( )
−
8
5 mhZ
May 2001