User's Manual

DM8-R Digital Modulator Tray Tray Description
DM8-R Digital Modulator, Rev. 0 2
DM8-R Modulator Tray
Overview
The DM8-R modulator Tray is an ATSC compliant 8 VSB modulator that mounts in a
standard 19” rack. The DM8-R modulator accepts a SMPTE-310 MPEG data stream and
outputs a 6 MHz wide IF output centered at 44 MHz with a pilot carrier at 46.69 MHz.
The DM8-R modulator provides linear and nonlinear correction capability for the
transmission path as well as internal test sources that are used during initial transmitter
installation. All of the functions of the DM8-R modulator are controlled from the LX
Controller LCD display and pushbuttons.
Inputs and Outputs
The inputs and outputs of the DM8-R modulator are described in the table below.
Description
Reference
Designator
Function
IF Output J4
Provides a 44 MHz IF Output with a 50
ohm output impedance
10 MHz Input J3
10 MHz input to the DM8-R modulator.
Provides the reference frequency to the
pilot VCXO.
SMPTE-310M Input J2
SMPTE-310 input that provides the MPEG
stream to the modulator.
110/220 VAC J1 Input Power to the Modulator
Front Panel Interface
The following table describes the connectors and indicators on the front panel.
LED Indicator or
Connector
Function
PWR Indicates that the DC power supply is operating
MPEG
LED
Indicates the presence of a valid MPEG stream at the
J1-2B input
PLL A
LED
Indicates that the DM8 symbol clock is locked to the
frequency of the 10 MHz reference.
PLL B
LED
Indicates that the pilot frequency is locked to the
incoming 10 MHz reference.
IF Sample Jack
BNC
Provides a sample of the IF output from the modulator
at approximately a –20 dBm level.
RS-232 SERIAL Serial Port used for initial modulator alignment