TELE-audiovision - The World’s Largest Digital TV Trade Magazine - page 46

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TELE-audiovision International — The World‘s Largest Digital TV Trade Magazine
— 1 -12/2013
Echo
Measurement
The Deviser S7000 can
also perform Echo measure-
ments, critical for DVB-T/H.
This makes it possible to
optimally erect an antenna
such that the interference
caused by a second, more
distant transmitter can be
eliminated.
When this second trans-
mitter lies outside of the
so-called Guard interval, an-
noying runtime delays are
the result that the demodu-
lator can no longer com-
pensate for. This leads to
interference and, at worst,
a total loss of reception. A
technician armed with the
S7000 can solve this prob-
lem in which, for example,
he can set up two antennas
and offset them such that
the incoming interference
signals would simply cancel
each other out.
The principle behind this
is that both antennas are
aligned to the nearest trans-
mitter and the interference
coming from the distant
transmitters would involve
turning the antenna to re-
ceive them.
If the offset of the two an-
tennas is selected cleverly,
then the signals from the
two nearby antennas would
add to each other while the
signals from the distant
transmitters would cancel
each other out.
Since these types of in-
terference echoes did not
exist near our test center
this type of interference was
not a problem here although
with the S7000 it would have
been very easy to set up
such a “double antenna”.
The ability to confirm your
actual position with the in-
cluded GPS antenna is actu-
ally quite interesting. In this
way you could use the S7000
to create regional reception
maps.
Too bad you can’t save sig-
nal strength measurements
automatically with the local
position so that they could
later be uploaded to a PC
or exported in Google Maps
format. Deviser will most
likely incorporate this func-
tion in a future firmware up-
date. This would allow you
to drive around a selected
region and at the end you’d
have an automatically gen-
erated field strength map.
Exercise:
MUX analysis of
a self-generated
transport stream
To test the Deviser S7000
as a TV analyzer, a scenario
was set up in a head-end
station. A professional IRD
with an integrated multi-
plexer receives a transpond-
er via the built-in DVB-S2
tuner and from a second IRD
via the ASI-IN interface. The
two transponders are then
muxed together into a new
transponder that is sent to
the ASI output.
The S7000 was connected
to this output with the goal
Mux TS Analyser
28. In order to use the Transport
Stream Analyser of the S7000
with the ASI input, you have to
first enable this interface.
29. By pressing the TV key on the
meter, you enter the Transport
Stream Analyser, which is now
receiving the TS stream on its
ASI input connector. In this case
I setup a TS containing channels
from two different German FTA
transponders.
30. The Deviser S7000 gives
access to all parameters of the
TS stream. 31, 32. Interestingly,
the equipment used to generate
this mux filtered all NIT infor-
mation, which is correct. Don’t
you hate receiving a CATV tran-
sponder containing a satellite
NIT?
33. One important application
for the S7000: determining the
TS rate. Notice on this picture
that the specified bandwidth of
the TS is 75 MB/s, but 32.45%
are not being used. This clearly
represents a waste of allocated
bandwidth.
34. I reduced the bandwidth on
the multiplexer to 35 MB/s but
this time the S7000 indicates
that there is 0% empty capacity
in the stream. This means that
there is no reserve for sporadic
increases in bandwidth.
35. Again, the multiplexer was
setup, this time to use a band-
width of 40 MB/s. And this time
around 15% of the bandwidth is
empty, leaving some reserve.
This adjustment took a couple of
minutes and resulted in saving a
bandwidth of 35 MB/s.
36. To compare our TS with one
of the originally broadcasted
streams, we connected the ASI
output of one of the IRDs.
37. While there is no disturbance
in the PCR interval measurement
in our TS…
38. …some can be detected from
the satellite signal, which is
normal after travelling back and
forth into space. However, if the
TS from our multiplexer would
show a PCR like this, then some-
thing would clearly be wrong.
39. Analysis of one of the origi-
nal satellite Transport Streams.
40. The PIDs carry different num-
bers…
41. …and the NIT contains addi-
tional data.
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