Olson Technology OTOT-1000C-9-FQ - Manual (Page 6)

EXTERNAL CONTROLS AND TEST POINTS
INITIAL SETUP
CAUTION:
There are two external DC test points. One reads laser current at 1V per 50mA. A typical
laser current of 30mA would read 0.6V at this test point. The laser power test point is
0.1V per mW. This is for historical tracking. The optical power meter is a much more
accurate means of measuring power. Both of these test points should be measured with
a high impedance voltmeter. There is an external multi-turn RF input attenuation control
on the front panel. This is set at the factory to the fully clockwise position which yields
minimum attenuation. The user can add 4dB of attenuation with this control which
allows the input RF level to be up to 4dB higher than the recommended levels. There is
an external 75Ω RF test point. This test point measures the laser drive level, not the
RF input level. This test point has been adjusted to read a very specific level when the
RF drive has been adjusted for optimum optical modulation. For the factory tested input
loading of 77 analog and 42 digital channels, this test point should read +10dBmV at
547.25MHz with the RF gain control pot is fully clockwise. At this frequency, the loss in
the connecting cable and any 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. worse than this will result in
ed 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
also
C-FF
Flatness
degrad NR
dB