Orban OPTIMOD 5750 Operating Manual page 124

6-7
Orban 5750 Technical Manual Technical Data
Because the 5750 does not digitize subcarriers applied to its subcarrier inputs, the 5750's MPX P
OWER meter (which
operates in the DSP domain) cannot indicate the power added by such subcarriers. These usually have constant
power, so it is easy to compensate for them. For example, if an FM subcarrier is injected at 4% modulation, it adds
power that can be calculated with an R.M.S. summation of the subcarrier and the rest of the composite signal.
Assuming that the subcarrier and composite signal are uncorrelated and that the composite signal is limited so that
its power is equivalent to a sinewave at 25.3% modulation, we calculate their R.M.S. sum as follows:
Recalling that the MPX POWER LEVEL meter is calibrated so that it indicates 0 dB when the composite output of the
5750 is a sinewave at –11.92615 dB below 100% modulation, we conclude that our subcarrier at 4% injection will
add 0.10694 dB to the multiplex power. Another calculation (not shown) indicates that 10% injection will add 0.62889
dB to the MPX power.
Multiplex Power Threshold: The 5750 provides a means to limit the integrated multiplex power to the ITU standard
by a technique that allows you to use any preset and to create customized presets freely. The multiplex power
controller is adjusted in the I / > U screen by the M P T
NPUT OUTPUT TILITIES ULTIPLEX OWER HRESHOLD control. Set it
O
FF if your country does not enforce the standard.
The control is located in the I / > U
screen because the regulation applies to operation of the
NPUT OUTPUT TILITIES
processor in a given installation.
Figure 6-11: Multiplex power over 15 minute observation interval
with Multiplex power controller active, measured at the Optimod's composite output