Promax MC-577 Manual De Instrucciones página 69

USER'S MANUAL MC-577.
- Tune the signal using the TUNING [25] and FINE TUNING controls [27] with the
help of the frequency counter display [23]. Turn the SPAN control [24] to select a
bandwidth so that the maximum signal on the monitor is the video carrier and the
minimum level signal is the noise. Remember that the noise can be measured, as
you wish, either inside or outside the channel.
- Release the audio control
- Read the measurement on the monitor with the help of the scale calibrated in dB
(10-60 dB) C/N [35]. If the signal level is close to 80 dBµV or is greater than this
value the signal should be attenuated using the RF attenuators.
If on taking the measurement the Noise Limit indicator [2] should light up, this
means that the actual noise level is less than the noise level of the MC-577 itself and,
therefore, the instrument can not measure under these conditions. In this event it can be
confirmed that the actual measurement is better than the one obtained (given that
the actual noise is less). One way to avoid this situation is to amplify the signal, though
then you will have to take into consideration the noise introduced by the amplifier.
EXAMPLE C.- Measuring the C/N ratio of an analogue signal
Take the following figure as an example, showing an analogue television signal:
Figure 10.- Measuring the C/N ratio of an analogue channel.
In the example in the previous figure it has been decided to measure the C/N ratio
inside the channel, in other words the noise is measured inside the channel at the point
where the content of the video signal is the minimum.
From the C/N scale [35] you obtain a C/N ratio of 41 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 41 dB.
05/2003
[28] to show the C/N measurement bar.
Measurement conditions:
Video carrier freq.:
RF attenuation:
Mode:
Noise Limit indicator
520.25 MHz
10 dB
ANALOG
ON
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