Olson Technology SA6940-RT - Manual (Page 7)

025-370548 REV X1 Page 7
CHANNEL LOADING
Olson SA6940-RT DFB/CWDM R-TX’s have a minimum of 7dB additional gain available for CNR improvement in lower channel or
bandwidth loading scenarios. For example, if only two channels (or 12MHz loading) are used, the Input Loading Curve (see Figure
4) allows for an additional 5dB of RF input level without inducing laser clipping to improve the CNR level accordingly.
The optimum RF drive level for the SA6940-RT is 7.0dBmV per channel with a standard loading of six analog video channels (or 36MHz
loading). The chart below shows the change in RF input level according to the amount and type of channel loading. The chart shows
on the right what the RF drive level should be to the transmitter. If loading with data channels only (QPSK, QAM) refer to the amount
of total bandwidth the data channels are consuming. 7.0dBmV per analog video channel is equivalent to -53dBmV/Hz with +15dBmV
per carrier at node input. With a standard 4/1 combiner installed in the node, there is 8dBmV of loss through the node (not counting
the PAD loss for each port) before the return test point at J6. To achieve +7dBmV at the transmitter with a zero PAD in each port, an
input level of +15dBmV will be required. A typical NPR curve is shown in Figure 5 on the next page.
Figure 4 - SA6940 DFB Input Loading