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www.TELE-satellite.com —
06-07-08/2012 —
TELE-satellite International —
全球发行量最大的数字电视杂志
corresponding QAM chan-
nels.
To find out how foolproof
the unit is, we intentionally
changed the settings for one
QAM channel. Instead of the
default 256QAM constel-
lation, we set 64QAM. Im-
mediately, the front panel
LED indicator assigned to
the channel as well as its
counterpart on the PC moni-
tor changed from green to
amber. After clicking it on
the PC monitor, a window
popped up listing all the pa-
rameters of the channel and
the cause of the problem be-
came obvious. The total bit
rate of all TV and radio chan-
nels from the selected satel-
lite transponder was greater
than what the QAM channel
modulated with 64QAM with
6.9 Ms/sec symbol rate can
carry.
If you are a little bit fa-
miliar with digital TV, you
know what to do. You can
either increase the sym-
bol rate (but normally, you
would not like to do that as
this would interfere with the
adjacent channels), increase
the QAM to maybe 128QAM
(and if this is not enough, to
256QAM) or remove some
TV channels from the satel-
lite content to be included in
the QAM channel. We did the
last thing and after blocking
two TV channels the total bit
rate decreased enough to be
handled by the 64QAM and
6.9 Ms/sec channel. All LEDs
were green again.
We decided then that it
was time to take a few meas-
urements at the outputs of
the BluBox 16. We config-
ured 8 channels of one mod-
ule of the unit in such a way
that every second cable TV
channel was occupied. We
did so for easy channel iden-
tification in a spectrum view
of a signal analyzer that we
connected to the output. Of
course, the BluBox hardware
is good enough to generate
adjacent cable channels. 8
QAM channels appeared at
the output of the module as
expected. As you can also
see it for yourself on the at-
tached photos, there were
no spurious signals visible in
the spectrum but only eight
very clean modulated carri-
ers.
After such promising be-
ginning, we configured the
second module in a similar
fashion but selected differ-
ent channel frequencies of
course. After connecting the
output of the first module to
the QAM input of the sec-
ond module we measured
the signal at the output of
the second module where
the summary signal of both
modules was expected. All
16 QAM channels looked
brilliantly. See the picture.
We checked that we can
see the videos of the TV
channels transmitted in the
QAM channel and took a
few measurements. As we
expected, the purity of the
signal was tremendous - al-
most no noise at all. MER at
37.3 dB and BER < 0.9 E-9
were at the end of our me-
ter’s scale. The measured
signal power was match-
ing the settings done in the
BluBox 16 very well. We
checked that indeed you are
able to set the output power
of all QAM channels in the
range: 62...82 dBµV in 1
dBµV increments as stated
in the specifications.
But you can do more than
that when setting signal lev-
els. The BluBox 16 lets you
set individual deviation in
signal levels of various QAM
channels from -6 through +3
dB in 0.5 dB steps. We did
the maximum increase for
one channel and maximum
decrease for another chan-
nel and took the photo. Eve-
rything worked as expected.
By adjusting the power of
individual QAM channels you
are able to compensate for
the losses in a cable net-
work. Normally, you will