Page 134 - TELE-audiovision - The World’s Largest Digital TV Trade Magazine

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134 TELE-audiovision International — The World‘s Largest Digital TV Trade Magazine — 03-04/2013 —TELE-audiovision.com
has the capability to automatically
measure and display the frequency of
a periodic signal.
Our interest in the DSO201 has to
do with a big problem that can be en-
countered in a satellite antenna instal-
lation. Customers routinely complain
that they can’t receive every channel.
Many times the cause of this is faulty
supply voltage to the LNB, a defective
22kHz signal, sometimes it’s a defec-
tive tuner and very often it’s simply
the LNB that is no longer up to snuff.
Most satellite signal analyzers can’t be
used to troubleshoot these problems
especially when there are no substi-
tute receivers or LNBs.
An oscilloscope, on the other hand,
can quickly pinpoint the cause of the
problem:
• 14/18V Troublesooting: To check
and see if the LNB is getting the proper
voltage, a multimeter would be good
enough. The voltage measured at the
inner conductor should be 14VDC for
vertical polarization and 18VDC for
horizontal polarization. But with the
1. 14.1V and a straight line – the LNB
was switched to the vertical low band.
2. The tuner provides the 22kHz
signal to switch to the high band. The
DSO201 automatically displays the
signal in the upper right. The shape
of the signal is quite good indicating
that the tuner is using an optimal
signal generator.
3. Checking the tuner of a receiver.
The 22kHz signal in reality is
only 21.8kHz and the voltage
level averages 18.9V (horizontal
polarization). This is all OK to
guarantee the proper switching of the
LNB.
4. With another receiver the frequency
is 22.8kHz and for the vertical
polarization we measured 14.4V.
5. With this receiver the signal
doesn’t exactly look like a square
wave yet it’s still correctly interpreted
by our LNBs; the DSO201 also
indicates an acceptable frequency of
21.8kHz.
6. Even DiSEqC commands can be
displayed by the DSO201 but for the
most part they can’t be interpreted.
But at least you can confirm that a
signal is being sent and also arriving
at the input of the multiswitch. While
the DiSEqC command is being sent,
the 22kHz signal is momentarily
interrupted!
7. Here the DSO201 is displaying a
video line. Clearly recognizable to the
left is the black edge band and the
line synchronization pulse as well as
the black edge band on the right side.
8. Almost everyone has already seen
an audio signal on an oscilloscope.
DSO201 this voltage can not only be
measured, it can also be monitored
over a short period of time so that, for
example, any dropouts or pulses can
be made visible.
• 0/22kHz Signal: More and more
often we see older receivers or signal
analyzers that can no longer properly
switch to the high band. The question
the installer has to answer: is the tun-
er defective or is it the LNB? With the
DSO201 you can instantly determine if
the 22kHz signal is available and if it’s
of sufficient quality. In theory it should
be a square wave signal but in reality
different receivers produce very indi-
vidualized switching signals.
• DiSEqC Commands: Another prob-
lem could be faulty switching between
different satellite positions. DiSEqC
switches have a tendency to fail es-
pecially if they’re mounted on the
antenna mast. In our experience the
life span of a DiSEqC switch is about
four years before at least one input
no longer functions correctly. The
DSO201 can’t be used to interpret the
DiSEqC commands, but they can be
made visible. So, the DSO201 can be
used to confirm that the signals are
being sent and that they are reaching
the corresponding multiswitch.