RFL 9780 RFL Electronics Inc.
April 8, 2003 2-17 (973) 334-3100
The output of the Transmitter Module is fed into the Power Amplifier Module. (The Power Amplifier
is the only rear-mounted module other than I/O modules.) The Power Amplifier boosts both the
voltage and current to provide the specified 10 watts of transmit power.
The Power Amplifier also contains a circuit which detects a loss of transmit carrier. This is used to
indicate a failure of the transmit circuits. Additionally, the Power Amplifier uses advanced feedback
techniques to emulate the desired 50 ohm output impedance. Not only does this increase the inherent
efficiency of the amplifier, but allows for the output impedance to be adjustable to match the actual
impedance of the line. See Section 9 for more information about the Power Amplifier Module.
In order to remove any unwanted harmonics from the amplified carrier signal, the output of the Power
Amplifier is followed by the Output Filter. The Output Filter is a passive bandpass filter. In order to
avoid having to make detailed adjustments to the filter or, worse, risking poor impedance matching at
either the input or output of the filter, several filters are available, several with jumper-selectable sub-
bands. This provides an easy and accurate method of setup. See Section 10 for more information about
the Output Filter Module.
Often the output of the Output Filter will be sent through a hybrid. The hybrid may be used to combine
the signals of two transmitters or to combine a transmitter and receiver without swamping the received
signal by the strong transmit signal. See Section 18 for more information about Hybrid Modules.
The output of the transmitter circuits must be fed out to the field wiring. This is accomplished on a Line
I/O Module. Various Line I/O Modules are available to meet the varied needs in the industry. All of the
modules provide one or more UHF connectors for the carrier and protection circuits. See Section 17 for
more information about the Line I/O Modules.
One significant alteration to the transmit description above is when an external power amplifier is used.
This may be required if more than 10 watts of output power is needed. In this case, the Power Amplifier
Module is omitted from the chassis. Additionally, there would be no need for the 9780 Output Filter or
Hybrid, as these would be required after the external power amplifier.
2.9.2 RECEIVER SECTION
The function of the receiver section is to monitor the received signal for the proper sequence of carrier
signals. For clarity, this Section discusses only the analog functions that detect the received
frequencies, interpreting this information is discussed in Section 14. The receiver consists of Line I/O
Module, RF Input Module, IF/BF Module, CLI Module, and LM/SL Module. There may also be a
hybrid in the receive path.
The received signal enters the 9780 chassis through a Line I/O Module. Various Line I/O Modules are
available to meet the varied needs in the industry. All of the modules provide one or more UHF
connectors for the carrier and protection circuits. Line I/Os used for received signals have additional
circuits for impedance matching and to protect the sensitive receiver front end. See Section 17 for more
information about the Line I/O Modules. If a hybrid is used to separate transmit and receive signals, the
protection and impedance matching circuits are located on the hybrid.
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