Promax MC-377+, Инструкция по эксплуатации

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INSTRUCTION MANUAL MC-377+.
Page 30
May 2001
4.2.6.3.2 Measuring the C/N ratio of digital channels
The C/N ratio of digital channels is measured in a similar way to analogue signals,
but remember that for the instrument to interpret the signal as being digital you should
select the digital signal measurement mode: simply, the DIG key [11] should be in the
pressed position and the DIGITAL indicator [30] should remain lit.
EXAMPLE D.- Measuring the C/N ratio of a digital channel
Audio control [27] released. Audio control [27] pressed.
Measurement conditions:
Frequency : 650.00 MHz
RF attenuation: 0 dB
Noise limit indicator ON
Figure 11.- Measuring the C/N ratio of a digital channel.
The previous figure shows the image appearing on the monitor when the audio
control [27] is released (left) and when it is pressed (right, showing the C/N
measurement bar). You are advised to adjust the SPAN control [23] so that there is no
C/N measurement bar, as this may mask a signal from a lower adjacent channel and
spoil the measurement.
From the C/N scale [34] (grey background) you obtain a C/N ratio of 21 dB.
Given that the Noise Limit indicator [2] was lit when the measurement was taken,
we may come to the conclusion that the C/N ratio is greater than 21 dB.