Olson Technology MUSCLE-1000C - Manual (Page 7)

analog channel loading. The factory test input is 77 analog channels with 42 digital
channels at 6dB down. The number of equivalent analog channels is 77 + 42/4, which
equals 87.5. This is the 87.5 ch / +17.6dBmV input point on the graph. Some systems
use an OMI meter to set laser modulation. The OTOT-1000C’s have been individually
adjusted for optimum performance. Setting all units for the same OMI, instead of using
the test point, will result in reduced transmitter performance. If the channel loading is
less than 40, you may decide not to increase the levels by the maximum possible
amount. This will provide improved distortion at the cost of CNR. The best rule of thumb
is to use the maximum possible levels for long haul links, and lower drive levels as the
links get shorter.
Short links can have reduced performance due to receiver overloading. Reducing the
laser RF drive will cause reduced CNR performance. Attempting to lower the laser
output power will have the even worse result of degrading both CNR and IMD. The
correct solution is to lower the receiver input level with an optical attenuator such as the
OTOA-1000. It is recommended that this be done at the receive location.
REDUCING LINK GAIN
Figure 2 - Input Level vs. Channel Loading - Low-Power Units