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ENGLISH
TV & SAT Level Meter MTD 120
User Manual
4.9.1.3.- Measuring the Carrier / Noise Ratio (C/N)
The MTD 120 offers two ways to make this measurement:
Auto:
The MTD 120 defines the frequency where noise level is measured automatically.
Reference noise:
The user defines the frequency where noise level is measured (by means of the Reference noise function). This frequency
will be used to measure noise level for all channels.
To select the measuring method activate the TV mode functions menu by pressing key ENTER [5], then use keys
[6] to select C/N
setup function and finally press key ENTER [5] again. The monitor will show a screen displaying two possibilities: C/N (Auto) and C/N (Reference
noise), then use keys
[6] to select the desired option and finally press key ENTER [5] to confirm.
When selecting the C/N (Reference noise) mode it is necessary to define the noise frequency: access the functions menu and now use keys
[6] to select Reference noise function and finally press ENTER [5] again. A screen titled REFERENCE NOISE will be displayed showing
the noise frequency in use. To change it press key SHIFT [31], the current frequency value will disappear and, using the keyboard, you will be able to
enter the new reference noise frequency in MHz and with two decimals figures. This frequency also can be modified in the Spectrum operation mode
(see 4.10.2.2. C/N (Referenced Measurement).
The MTD 120 carries out C/N ratio measurement in four different ways, according to the carrier type and the band in use:
A) Terrestrial band, analogue carrier
Carrier level is measured using a quasi-peak detector (230 kHz BW). Noise level is measured with an average detector and corrected to refer
it to channel bandwidth (according to the standard in use).
B) Terrestrial band, digital carrier
Both measurements are done with an average detector (230 kHz) and the same corrections are introduced on them (bandwidth corrections).
C) Satellite band, analogue carrier
Carrier level is measured using a quasi-peak detector (4 MHz BW). Noise level is measured with an average detector (4 MHz) and corrected
to refer it to channel bandwidth.
D) Satellite band, digital carrier
Equivalent to case B but now using the 4 MHz BW filter.
On selecting the Carrier / Noise measurement mode the screen displays the following information:
Figure 8.- Carrier-to-noise ratio measurement (Satellite band, analogue signal).
As well as the video carrier / noise level ratio (20.1 dB in previous figure), the frequency or channel (depending on the tuning mode
selected) and the level of the video carrier and noise level are also shown.
When measuring channels in the satellite band or digital channels, to measure the C/N ratio correctly, the bandwidth of the channel must be
defined previously, using the Channel BW function on the TV mode functions menu.
IMPORTANT REMARK
To measure digital channels C/N ratio in Auto mode it is indispensable to tune channel at its central frequency.
IMPORTANT REMARK
In the case of an analogue terrestrial signal, when C/N (Auto) mode is selected, the MTD 120 performs an in-channel
measurement, this involves that C/N value will take several seconds to stabilize (six seconds at the most). An arrow below the C/N
readout represents the measurement cycle and it is necessary to wait the arrow passes twice on the same point to guarantee a
correct measurement.
C/N (Auto)
20.1 dB
VIDEO CARRIER:
Frequency
=
1345.5 MHz
Level
=
64.1 dBuV
NOISE:
Frequency
=
1329.5 MHz
Power
=
44.1 dBuV
Channel BW =
32.0 MHz
