Promax 8 plus Manual Del Usuario Y Operador página 81

INSTRUCTION MANUEL. PROMAX-8+
In order to measure digital channels correctly, previously, the channel must be
defined as digital (see Edit Channel Plan function at section '4.2.1 Unit Global
Configuration) and, if necessary, the CHANNEL BW parameter should be
redefined by means of the Channel-Frequency configuration menu. When a
channel has been defined as digital, the PROMAX-8+ tunes it at its central
frequency.
Digital channels power measurement is carried out by means of an integration
method. The PROMAX-8+ divides the bandwidth of the channel (CHANNEL BW) in
sections of 230 kHz (4 by each MHz approximately) and measures the contribution of
each one to the total power of the channel. This way, a very exact measurement is
obtained, specially in the case of degraded channels, because the channel flatness is
had in consideration.
Figure 20.- Measuring the power of a digital channel by integration.
The C/N ratio measurement shows the ratio between the digital channel power
and the noise power. The user can define the frequency where the noise power must be
measured. Two possibilities exist:
I. Absolute method
Selecting in the Channel-Frequency configuration menu the NOISE MODE
parameter as FREQ, the equipment will interpret the NOISE FREQ. value as the
frequency where the noise power measurement must be done. Naturally the user must
be sure that the NOISE FREQ. value corresponds with a free channel.
II. Relative method
Selecting in the Channel-Frequency configuration menu the NOISE MODE
parameter as F, the unit will make the measurement of noise at the frequency obtained
to add to the tuning frequency (channel central frequency) the value defined for the
NOISE FREQ. parameter. The PROMAX-8+ takes by default NOISE FREQ. = BW/2 +
0.5 MHz, where BW is the channel bandwidth defined in the channel plan, thus for
example, if it is desired to measure the C/N ratio of a digital channel with a bandwidth
(BW) of 8 MHz, NOISE FREQ. will take as value 4.5 MHz. The Channel-Frequency
configuration menu (paragraph 4.2.3.3) allows the user to redefine this parameter; when
tuning a new channel the equipment will return to assign to NOISE FREQ. the default
value.
May 2001
VERY IMPORTANT
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