User guide

DM-14B & DM-14C User’s Guide

N.B. With reference to fig. 8, the NETWORK name you can read in the centre to the right, e.g. NETNAME=SKY, is the

NET.ID table transmitted via satellite by the operator and which the instrument reads by extracting the information

from the MPEG data. However, the prog. name, read in the centre to the left under the word MENU, e.g. PROG

NAME: SKY1, is the one you, or your dealer, has pre-stored and can be varied only using a PC, opt. (see page 19).

N.B. When you activate MORE MEAS 3 (where available) and MENU, due to problems with space, the quality bar chart

and the level/power bar chart both respectively disappear. The white arrow, near to the quality bar chart, indicates

the minimum quality required to achieve a PASS in automatic tests.

32) C/N MEASUREMENT

In some cases the C/N measurement of analog signals may vary with the level because when the level increases

some RF attenuators could be inserted. The automatic insertion of attenuators reduces the instrument’s sensitivity

and consequently reduces the C/N read on the screen, which will be less than the real one. To avoid this carry out

the following procedure:

• Select normal spectrum mode (without activating the C/N measurement)

• Fix the span at 200 MHz when in AN-SAT (analog satellite)

• Fix the span at 10 MHz (or 20 MHz) when in AN-TV (analog TV)

• Increase the REF-LEVEL (reference level) using the UP key, in 1 dB steps, until you see the noise lower by

approximately 10 dB

• If the noise goes under the line at the bottom of the screen, change the spectrum scale and set it at 10 dB/DIV (this

may occur in analog sat mode)

• Press MENU and select the ΔMRK (delta marker) activate the C/N select.

WARNING: make sure you do not press MEAS or any other key, because the attenuators will set using

standard values.

• Using the UP and DOWN keys bring the marker to the point where you want to measure the noise and read the

C/N value (which will correspond to the measurement filter bandwidth), in the window in the lower part of the

screen (ΔMRK C/N),

• May we remind you that when you measure the C/N in analog TV or SAT mode with the _MRK (without

specifying the C/N), the band correlation is not carried out automatically. In this case you should subtract 10 dB

from the measurement value if you are carrying our a satellite measurement, and 16 dB from the value for TV

measurements.

33) C/N Measurements in emulated COFDM demodulation mode.

We suggest following these rules when carrying out emulated C/N measurements:

• Use C/N far when there are adjacent channels

• Always use C/N NEAR when there aren’t any adjacent channels

• If you are carrying out measurements on a head-end with selective filters and channel converters, only use the C/N

near measurement. In this case the C/N far measurement could measure a higher C/N than the real value.

To fix a C/N far or C/N near measurement, activate the configuration menu (see page 10 which contains the

configuration menu description).