Promax PROMAX-4, User Manual

Page: 72 / 108

USER’S MANUAL. PROMAX-4
Page 30 Novembre 1999
APPENDIX D.- CARRIER TO NOISE RATIO (C/N)
The Carrier to Noise ratio is a measurement of the signal quality. The power of
the noise measured changes according to the resolution filter utilized. However, in TV it
is usual to refer the noise level to a bandwidth of 5 MHz. If the measurement is reduced
to a different bandwidth, the user must apply a simple correction. The PROMAX-4 takes
the measurement in a noise bandwidth of 5 MHz.
C/N = C
L
– N
L
(dB)
N
L
: dependes on the measurement bandwidth
N
L
= N
measurement
+ 10 log (BWx / BW
measurement
)
There is some standards that determine the minimum C/N value for an
installation. In general greater values than 40 dB are considered good quality signals.
Lower than 40 dB you can see snow or graininess at the display.