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TELE-audiovision International — The World‘s Largest Digital TV Trade Magazine
— 01-02/2013
ODU32 Input
Output 1 of QUAD GTU
Channel # Power
C/N
MER
Power
C/N
MER
dBµV
dB
dB
dBµV
dB
dB
41
75.2
35.8
23.1
79.2
33.4
21.7
45
74.2
36.8
24.7
79.7
33.4
24
48
70.6
33.5
21.7
79.2
33.6
21.6
Table. 2. Input and output of the optical system.
QUAD and QUATRO GTU de-
vices respectively) while not
degrading their quality and
thus not improving terres-
trial reception.
Thanks to the DTT head-
end we were able to check
the performance of the
GlobalInvacom system for
the lowest and highest DTT
channels. We simply shifted
channel 45 to channel 21
and later to channel 68 (474
and 850 MHz respectively).
We got practically the same
results as for the channel
45 located in the middle of
the UHF band: Power = 79.2
/ 76.2 dBµV, C/N = 33.6 /
32.3 dB and MER = 23.9 /
23.5
Before finishing our test,
we decided to verify one
of GlobalInvacom’s recom-
mendations, namely the one
for using a DTT processor
before injecting a terres-
tical system. See the results
in Table 2.
The signal at the output
was stronger than that at
the input and more uniform
– we noticed only a 0.5 dB
spread. This is the effect of
the automatic gain control
which is embedded in GTU
converters. The carrier-to-
noise was also very similar
for all three channels. How-
ever, we were most inter-
ested in the MER readings
as this parameters directly
reflects signal quality. As
you can see in Table 2, MER
degradation was very limit-
ed despite two conversions:
from RF to light and back.
Such conversion always de-
teriorates signal quality but
fortunately in the GlobalIn-
vacom system the changes
in MER between input and
output were really negligent
- from 0.1 to 1.4 dB depend-
ing on the channel.
Then, we checked if there
are any significant differ-
ences between the QUAD
GTU outputs. See the re-
sults in Table 3. Practically
all the outputs are identical.
All the measurements so
far were made without a
satellite signal. It was time
to check if adding a satel-
lite signal would have any
impact on the terrestrial
signal. We connected a
GlobalInvacom optical LNB
to the ODU32 and checked
that the full spectrum of the
IF satellite band is available
at the outputs of the QUAD
GTU. We repeated the
measurements of terrestrial
channel 45 on all four out-
puts. Table 4 presents the
results. You should compare
them with the numbers in
Table 3.
Table 4. Results for chan-
nel 45 for all four outputs
the MER was unaffected.
This means: the terrestrial
signal quality was as good
as in the test without satel-
lite signal!
The same tests with the
QUATRO GTU gave even
better results. Without a
satellite signal we had a
channel power around 80
dBµV, C/N around 34.5 dB
and MER around 24.3 and
after adding the satellite
signal, power decreased
only to 75.5 dBµV while
C/N and MER remained the
same.
The conclusion is: the
presence of a satellite sig-
of the QUAD GTU with the
presence of satellite signal.
The output power de-
creased by 10 dB but was
till quite high – around 70
dBµV. But we were ex-
tremely happy to notice that
nal in the optical system
influences only the output
power level of terrestrial
signals (by 10 dB or 5 dB for
trial signal into the optical
system. When we measured
the terrestrial signal before
the DTT processor and after
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