Specifications

Section L
Modulation Encoders (A25-A29)
L.1 Introduction
This section describes the Big Step Modulation Encoder and the
Binary Encoder boards. Topics include Function, Location,
Block Diagram Description, Detailed Circuit Description, Trou-
bleshooting, and Removal/Replacement.
NOTE: Parts List for this board is in Section VII.
L.2 Function
The Modulation Encoder board main function is to convert the
12 bit digital audio signal from the A/D converter into Turn
ON/TurnOFFsignalsforthe156BigStepand4BinaryStepRF
Amplifiers.
Each Modulation Encoder also has Module/Cable Interlock,
Fuse Fault Detectors, and a Programmable Big Step RF Ampli-
fier. Certain Encoders will monitor Air Flow and one detects RF
Amp Temperature. If an RF Mute is applied, the Modulation
Encoders will turn-off all RF Amplifiers and the power will drop
to zero Watts, without turning off the RF Amp Power Supply.
The DX100-3F uses five Modulation Encoder boards (A25-
A29).
A29 controls the Big Steps RF1-RF31/RF152 and monitors the
temperature of RF1.
A28 controls the Big Steps RF32-RF62/RF153 and monitors the
air flow in the left PA compartment.
A27 controls the Big Steps RF63-RF93/RF154.
A26 controls the Big Steps RF94-RF124/RF155 and monitors
the air flow in the center PA compartment.
A25 controls the Big Steps RF125-RF151/RF156, Binary Am-
plifiers B9-B12 and monitors the Air Flow in the right PA
compartment.
Big Steps RF152-RF156 are the Programmable RF Amplifiers.
L.3 Location
Mod Encoders A29 and A28 are located in the left PA compart-
ment (SEE VIEW 14).
Mod Encoders A27 and A26 are located in the center PA com-
partment (SEE VIEW 12).
Mod Encoder A25 is located in the right PA compartment (SEE
VIEW 10).
L.4 Big Step Modulation Encoders
L.4.1 Block Diagram Description
Refer to Figure L-1 Modulation Encoder block diagram for the
following discussion.
L.4.1.1 Digital Audio Flow
For the following discussion, refer to Fig. L-1, Mod Encoder
Simplified Diagram.
The Digital Audio Input from the A/D Converter is transferred
into the Input Latches on each Modulation Encoder board.
The Data Strobe signal drives the clock input of the Input Latches
and EPROM Encoder Latches. It transfers the data present at the
inputs to the Latch outputs and holds the outputs at a constant
level until the next Data Strobe signal from the A/D Converter
occurs.
The eight Most Significant Bits of the Digital Audio Input B1
through B8 address EPROM Encoders. Each EPROM encodes
the 8 bits and provides 8 outputs in a counting pattern determined
by the Program Selector. One EPROM Encoder controls 8 RF
Amplifiers, with 4 EPROMs per Modulation Encoder. The out-
puts of the EPROM are stored by Latches until the next Data
Strobe.
The outputs of the Latches go to Encoder Output Drivers which
are powered by the B+ and B- voltages. Their output provides
proper turn-on/turn-off voltages for the RF Amplifiers assigned
to that Modulation Encoder.
A Program Selector Switch and a Programmable RF Amplifier
Control circuit will allow the user to substitute a designated
programmable RF Amplifier in place of another RF Amplifier
should it be required.
If an RF Mute is received or generated by the RF Mute Control,
the Encoder Outputs will turn-off all RF Amplifiers.
L.4.1.2 B+/B- Regulators
When the TX On Enable input goes high from the Controller, the
B+/B- Enable switch will turn on the B+ and B- Regulators and
the Output Fault Sense detectors for both supplies. Should either
supply be incorrect, a Supply Fault will be sent to the Controller
and the transmitter will be shut OFF.
When the TX On Enable input goes low,the B+/B- Enable switch
will shut down the B+/B- Regulatorsand disable the Output Fault
Sense detectors.
+12VDC is applied to the B+ Unregulated Input, where it sup-
plies the +5 Volt Regulators, Bypass Fusing and Regulation for
the Bypass mode, and Fusing And Protection for the B+ Regu-
lator.
The output of the B+ Regulator is a constant voltage that passes
through Output Protection and is applied to the Normal Mode
jumper. -12VDC is applied to Fusing And Protection and sup-
plies the B- Regulator. +12VDC from the Fusing And Protection
also supplies the B- Regulator.
888-2339-002 L-1
WARNING: Disconnect primary power prior to servicing.