Diamond TX Series - RF Signals

Transmitters 9 November 2001 93
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Tran sm it te r
RF Signals Input Ports: RF signals from the shelf backplane enter the
transmitter through RF connectors on the rear of the
transmitter module. The recommended RF input level
depends on the channel loading used.
In the 800E-TX and
800G-TX transmitters,
auxiliary RF signals are
injected after the
pre-amplifier hybrid. This
helps to provide higher
isolation between the
auxiliary and main RF input
ports.
• Main RF input allows primary RF signals to enter the
module.
• Auxiliary RF input (not available on the DT-QTX) allows
injection of auxiliary RF signals for applications such as
targeted services (local programming).
Combiner: Auxiliary signals are attenuated by an internal
directional coupler, yielding lower levels than those of the
main RF input. See specifications for details.
Variable PIN Attenuator: After passing through the
combiner, RF signals then pass through a variable PIN
attenuator, adjusted by AGC or manual gain control. The PIN
attenuator allows you to adjust, either manually or
automatically, the RF drive level by ±3 dB.
Pre-amplifier Hybrid: Next, a hybrid amplifies the signal.
RF Test Point (Drive Level Monitor): A directional coupler
directs a portion of the amplified signals to the RF drive level
monitor test point, which is used to adjust the RF drive to the
optimum level. Using this test point, you can adjust the
transmitter’s gain for –20 dB relative to the laser’s RF drive
level. (See specifications.) This test point is accessible through
the transmitter’s front panel.
Post-amplifier Hybrid: A post-amplifier hybrid amplifies the
RF signals.
Gain Control Circuitry: The 800E-TX and 800G-TX series
transmitters offer three AGC modes: Customer AGC (AGC
On with customer-optimized OMI), Factory AGC (ACG On
with factory-set OMI), and Manual (AGC Off). Other DT-TX
series transmitters offer Manual and Factory AGC modes
only. The DT-QTX series does not offer AGC.
If the transmitter is set to manual gain control mode, use the
manual gain control, a potentiometer accessible through the
front cover of the transmitters, to adjust the variable PIN
attenuator.