Figure 20.- Carrier to Noise measurement in Spectrum mode (digital channel).
To define the frequency to measure the noise, select the Reference noise function in the Spectrum functions menu and press key
ENTER [5]. Next, again in the Spectrum mode, press keys
[6] to place the marker on the frequency where you want to measure noise
level or press key SHIFT [31], current reference noise value will be erased and using the keyboard introduce the new value. Finally accede to
the functions menu again and execute the Carrier function so that you can tune new carrier frequencies by keys
[6].
When C/N measuring mode is selected, on the lower part of the image appears the tuned frequency/channel ( Carr.), the noise frequency
(Noise), the carrier Level (if analogue mode is selected) or the channel Power (if digital mode is selected) and the carrier to noise ratio (C/N).
4.10.2.3.- Measuring the Power of Digital Channels (Channel Power)
In the Spectrum Analyser mode the MTD 120 measures digital channel power using an Integration method between channel limits
which are defined by the user. To show the interest of this method, imagine a spectral distribution like the one shown in the following figure
(channel bandwidth is 8 MHz defined by the markers). If channel power is measured in TV operation mode different readouts will be obtained
depending on the tuned frequency (measurement filter bandwidth is 230 kHz), if tuning is shifted from 759 MHz to 762 MHz reading will
increase in several dB.
Figure 21.- Channel power measurement in Spectrum Mode.
When measuring Channel power, on the lower part of the image appears the tuned frequency (or channel), the channel bandwidth
(Channel BW) and the Channel Power.
To measure the channel power, first of all it is necessary to define channel bandwidth, that is to say to set the limits of the integration:
select the Channel bandwidth function in the functions menu and then, again in the Spectrum mode, press keys
[6] to modify it or
well press key SHIFT [31], current channel bandwidth will be erased and using the keyboard introduce the new value. Finally accede to the
functions menu again and execute the Marker function in order you can tune new carrier frequencies, then when pressing keys
[6],
the tuning marker and the channel bandwidth limits will shift together.
80
70
60
50
40
760.00 MHz
Channel Power:
Channel BW: 8.00 MHz
55.0 dBuV
Channel bandwidth
Marker
70
60
50
40
30
Carr.: 650.00 MHz
Power: 44.0 dBuV
Noise: 655.0 MHz
C/N: 12 dB
Channel BW
Carrier
Reference noise
136
TV & SAT Level Meter MTD 120
User Manual
