Autosetup, Automatic Gain Control, and Manual Gain Control
PWRLink™ II 4100S Series Optical Transmitter Product Manual Rev A (3/06)
4–5
What if the video loading is less than 80 NTSC (System M) carriers?
When the number of video channels is less than 80 and you require better
CNR, you can increase the input level as shown in Figure 4-2 on page 4-5.
The Autosetup procedure will measure the RF input level and adjust the
pad value for operation as close as possible to optimum performance.
Figure 4-2. RF drive level as a function of channel loading
Even if you plan to add more video channels in the future, Harmonic
recommends that you use 15 dBmV per channel to ensure that the system is
easy to upgrade.
When should CW Mode or Video Mode be used?
The choice of mode depends on the loading.
Example
In the case of a transmitter with the following setup:
•
Loading: 80 unmodulated NTSC (System M) channels from 50 to 550 MHz
and 200 MHz digital loading from 600 to 800 MHz –10 dBc down
•
RF input level: +18 dBmV per channel
•
Factory optimized pad value at 15 dBmV per channel: 5.5 dB
In the case of CW unmodulated carriers:
Harmonic recommends running
Autosetup in CW Mode. In the factory, the transmitter is optimized using
unmodulated carriers. Therefore, running Autosetup in CW Mode with the
same channel load as the factory returns the pad level to close to the optimal
value. In this case, if you use Autosetup
⊕
CW Mode
⇒
Pad value
will be 5.5 + (18-15) = 8.5 dB.
