Pagina 45 - TELE-satellite - La Più Grande Rivista del Mondo Sul Commercio TV Digitale

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45 —
09-10/2012 —
TELE-satellite International —
21. Language selection: English, Dutch,
Turkish, Chinese
22. The DS2400T comes with an integrated
clock that can be used to add a timestamp
to each measurement.
23. Deviser has equipped the DS2400T with
enough memory capacity to also deal with
large-scale installations without the need
for a PC.
24. Measuring units can be adjusted to
meet personal requirements.
25. The DS2400T even allows user calibra-
tion, to make sure different meters used
within a company all give out the same
measurement results, for example.
26. Separate threshold values can be
defined for DVB-T, CATV and DVB-C, which
then flow into the automatic quality check.
29. The DS2400T comes with a built-in
voltage checker which can measure the
voltage arriving at the HF input.
30. What’s more, the current voltage of the
internal battery pack can also be checked.
31. And for the curious among you, it is
even possible to find out the inside tempe-
rature of the meter.
32. A number of different channel lists are
pre-stored in the meter.
33. Each channel list can include both
analog and digital channels. If you only
want to measure analog or digital channels
there is no need to set up additional chan-
nel lists. This is the menu item for channel
list configuration/editing.
ment modes we already looked at. When
I called up MER measurement, however,
I was simply at awe: At long last a manu-
facturer has come up with a convenient
hand-held device that is able to perform
long-term measurements which can ac-
tually be put to use by professionals.
With the DS2400T users can define a
period from one minute to several days
during which the meter will collect all rel-
evant data and then present the results
in a way that is nothing short of extraor-
dinary. The sheer amount of data does
not compromise usability at all. What’s
more, there is no need to connect the
meter to a PC for long-term measure-
ments. Installers can use this feature
to even detect occasional image faults,
something that is of enormous value and
can only be found in professional equip-
M-GRAM measurement
And that’s not all: It may sound too
good to be true but the DS2400T is ca-
pable of measuring the MER (modulation
error ratio) of individual carriers. Such
a measurement is often referred to as
‘MER versus carriers’ and is particularly
important for DVB-T. While most meters
only measure MER as the average across
all active carriers, only very few can give
separate results for each carrier of a
DVB-T transponder. Why is this so impor-
tant? In some scenarios a neighbouring
analog transmitter might interfere with
some – but not all – carriers of a digital
transponder, since analog transmitters
broadcast three relatively small frequen-
cy spaces for video, audio and colour. In
such a case the average MER value may
well look OK, even though reception is
not possible because some carriers ex-
perience massive interference while the
majority of carriers boast an excellent
signal. Conventional measurements can-
not identify such a problem, and you re-
ally require professional equipment such
as the DS2400T to get to the heart of the
matter. All you need to do is position a
marker above individual carriers to find
out the corresponding results of the MER
measurement. Moreover, MER measure-
ments have a peak hold function, which
means the current MER value is shown
in yellow, while the peak value is drawn
with red colour. Too good to be true? Yes,
but that’s what you should get used to
with this meter.
Echo measurement
Again, this is a measurement that is
particularly helpful for DVB-T signal anal-
ysis. A number of countries (including
Portugal, our test location for this report)
have opted to implement DVB-T as SFN
(Single Frequency Network). The advan-
tage of such an approach is that all broad-
cast cells use the same frequency so that
reception equipment can have the same
channel list irrespective of where it is
used. Mobile reception benefits greatly,
since you never need to perform a chan-
nel search while moving around within
a country’s borders. On the other hand,
all that glitters is not gold since single
frequency networks cause different lag
times in cases when a receiver is oper-
ated between two cells. In such a case
two slightly time-delayed signals with the
same frequency reach the receiver and
cause interference that is called echo.
DVB-T comes with an integrated correc-
tion mechanism that filters echoes up
to a certain distance. That distance is
referred to GUARD INTERVAL and ech-
oes that are produced within the guard
interval do not cause image interfer-
ence, while echoes exceeding the guard
interval will result in visible interference.