Olson Technology MUSCLE-1000C - Manual (Page 6)

impedance matching devices can be very significant. See the section on input loading
for the proper test point levels with other input conditions.
Mount the unit and apply power. The laser is temperature controlled. The unit will
operate immediately after turn on, but requires about 5 minutes to temperature stabilize.
Measure and record the optical output with a power meter. Measure and record the
laser current and optical power readings at the external test points. Measure and record
the RF input levels.
At this frequency range the loss and slope of coax
cables is very significant. The best approach is to connect the cable that will go to the
OTOT-1000 input directly to the measurement device. The input signals should be flat
within ±1dB, preferably within ±0.5dB. Responses worse than this will result in reduced
C
and or distortion performance.
Special attention must be paid to the relative level of the channel that is used to set the
RF gain and thus set the laser modulation. If this channel is much higher than the other
channels, then setting the RF gain will cause the other channels to be lower than
optimum, resulting in reduced CNR performance. If this channel is too low, then using it
to set the RF gain will cause the other channels to be higher than optimum, resulting in
reduced distortion performance. A 1
to 2dB error will cause significantly impaired
performance. Connect the RF input to the unit and adjust the RF gain control for a level
that indicates proper modulation. For the factory test condition, this is +10dBmV at
547.25MHz. For other channel loadings, consult the next section. Do not forget to
account for the loss in the connecting cable.
C
NR
dB
INITIAL SETUP
CAUTION:
INPUT DRIVE vs. CHANNEL LOADING
The laser RF drive level is the primary determining factor of link distortion and CNR
performance. The basic limitation on input drive is total input power. The following charts
show the approximate input levels versus channel loading. The left axis shows the
nominal RF input level. The unit will work with levels within ±2dB of this value. The right
axis shows the test point reading for optimum modulation. Figure 2 is for the OTOT-
1000C-3 and OTOT-1000C-6 models. Figure 3 is for all other optical power levels. Most
systems run their digital channels at 6dB below the analog channels. This is a very
convenient level for calculating loading. At 6dB down, simply divide the number of digital
channels by 4 and add to the number of analog channels to get the total equivalent