Fine Tuning Each Transmitter
PWRLink II 4800T Optical Transmitter Product Manual Rev A (2/02)
4–3
Example
In the case of a transmitter with the following setup:
•
Loading: 76 unmodulated PAL B/G channels from 45 to 870 MHz and
100 MHz digital loading –10 dBc down
•
PAL B/G carriers RF input level: +18 dBmV per channel
•
Factory optimized pad value at 16 dBmV per channel: 5.5 dB
In this example, the input level at 18 dB/ch is higher than the factory setting
of 16 dBmV/ch and there are two options for resetting the factory settings:
•
If you use MGC
⊕
Reset to Factory Settings
⇒
Pad value will be 5.5 dB.
•
If you use AGC
⊕
Reset to Factory Settings
⇒
Pad value will be 5.5 +
(18-16) = 7.5 dB.
If you use MGC
⊕
Reset to Factory Settings, the pad value will be 5.5 dB.
The laser is overdriven. To optimize the transmitter’s performance, you need
to adjust the RF input level to the factory setting, 16 dBmV/ch.
Using AGC
⊕
Reset to Factory Settings provides the adequate drive level to
the laser with a pad value of 7.5 dB.
4.2
Fine Tuning Each Transmitter
Fine tuning each transmitter is recommended to precisely fit your specific
requirements or preference. You can modify the transmitter configuration to
trade off CNR performance for improved CSO and CTB distortion
performance. Specifically, if you increase the RF pad by 1 dB, the following
results occur:
•
Transmitter CNR decreases by 1 dB
•
CSO decreases by approximately 1 dB
•
CTB decreases by approximately 2 dB
You can adjust the RF level by using any of the three interface options. For the
RF adjustment procedure using each of the interface options, see
4.5 Setup via NETWatch Site Controller
Transmitter’s Front Panel Controls
.
4.3
Autosetup, Automatic Gain Control, and Manual
Gain Control
The
Autosetup
feature enables you to quickly set the internal drive level to the
laser as close as possible to the optimal value determined at the Harmonic
factory. The transmitter operates in either the Automatic Gain Control (AGC)
mode or the Manual Gain Control (MGC) mode.
