CHAPTER 13: OPTICAL OUTPUT
13-4
MDU Solutions
®
– DVIS/DVISm - Digital Video Insertion System & Mini Digital Video Insertion System - Installation & Operation Manual
NOTE: Depending on the end devices (ONT, ONU, Forward Path Receiver) used in the field and
the resulting QAM performance of the DVISm inserted QAM channel compared to incident QAM
channels (QAM levels, MER, BER), it may be required to reduce the drive level from + 48dBmV to
a lower value. In such case the attenuator in the GUI
RF Output tab can be set to higher values
which adds attenuation to the DVISm generated QAM signal and thereby reduces the drive level
entering into the Optical Transmitter card.
NOTE: Resulting QAM performance may also be affected by the setting of optical levels, so if
problems are noticed, it is required to check in parallel both the inserted channel optical levels and
QAM drive level to the optical transmitter to obtain proper results. Setting optical levels is explained
later in this section. See also
“13.4.2 Setting Optical Insertion Level” on page 13-4
for further
information on possible adjustments for performance.
11. This concludes the setup of RF QAM level into the Optical Transmitter Card.
13.4 Optical Insertion Power Setting
NOTE: Please refer to the drawings in
“13.5 Optical Insertion Applications” on page 13-4
for
clarification of optical insertion points and
Δ
P Optical levels described in this section.
13.4.1 ΔP Setting
When setting the optical level of the DVISm QAM at the network optical insertion point and depending on the deployment
scenario, there is always a ΔP (difference in Optical Power Levels) between the incident optical power from the existing
system and the inserted channel power level of -10 to -13dB. That means the measured level of the inserted channel will be
10 to 13dB below the measured optical power of the incident channels.
NOTE: In the RPD based nodes scenario there is no
Δ
P. The optical level has to be set to
accommodate Forward Path Receiver input specifications.
13.4.2 Setting Optical Insertion Level
•
ΔP shall be between -10 to -13dB (Inserted power is below the incident power) at the insertion point.
•
Different end devices (ONT, ONU, Forward Path Receiver) may require different ΔP. It is advisable to always ensure
minimum -10dB delta as the starting configuration.
•
If starting with a ΔP of -10dB it is found that the incident optical QAM channels are affected by the inserted wavelength,
or that the resulting RF level of the inserted QAM channel is above the level of incident QAM channels (as measured
at RF output of ONT, ONU, Forward Path Receiver) it may be required to further increase ΔP from -10dB to a greater
Δ value between -11 to -13dB. Always increase optical ΔP in 1dB steps and redo QAM measurements.
NOTE:
If
Δ
P has been increased to 13dB and still the inserted QAM level is higher than the level
of the incident QAMs, it is suggested to try reducing the QAM drive level to the transmitter (to a
value less than +48dBmV) to obtain the desired results. Further adjustments may also be possible
by increasing
Δ
P beyond 13dB if the system design allows for such adjustment and no degradation
is being observed at resulting QAMs (QAM levels, MER, BER).
13.5 Optical Insertion Applications
With the optional fiber optic transmitter module installed it is now possible to use the DVIS platform for MDU QAM video channel
insertion in PON and RFoG applications such as FTTx. Depending on system architecture there are different possibilities of
where the optical insertion of the DVISm QAM channel may be done. Several typical applications are presented here but
these are not the only scenarios possible. Please contact your ATX Networks sales contact to discuss other possible variations
based on different system layouts. The sales contact will pass the query to the appropriate engineering department for review.
