User's Manual Part 2
Digital ATSC Exciter-Modulator System Chapter 3, Upconverter/Downconverter
Tray or Module Assemblies
Axcera Axciter, Rev. 0 42
Chapter 3: Upconverter/Downconverter Tray or Module
Assemblies
Upconverter/Downconverter Tray and Modules Overview
(NOTE: The boards contained in the stand alone Upconverter/
Downconverter tray and the boards contained in the Upconverter and
Downconverter sled assemblies are the same.)
The Upconverter/Downconverter Tray, used with Visionary IOT
Transmitters, contains (A7) a Final Conversion Board, Axciter (1307263),
(A5) a First Conversion Board (1306759), (A4) a L-Band PLL Board, Axciter
(1307206), (A3) an AGC Control Board, Axciter (1307366), (A2) an
Interface Board (1307383) and (A6) a Downconverter Board (1306807).
The Upconverter Sled and Downconverter Sled Assemblies are used with
Innovator Solid State Transmitters. The Upconverter Module Assembly
(1306850) contains (A2) a Final Conversion Board, Axciter (1307263), (A3)
a First Conversion Board (1306759), (A4) a L-Band PLL Board, Axciter
(1307206) and (A1) an AGC Control Board, Axciter (1307366). The
Downconverter Module Assembly (1306852) contains (A1) a Downconverter
Board (1306807). These two modules operate identically to the
Upconverter/Downconverter tray.
The 44 MHz IF input, -6 dBm in level, to the upconverter module assembly
is applied through the backplane board from the modulated IF input jack
located on the rear of the HX or LX exciter/driver chassis assembly. The
44 MHz IF input to the upconverter/downconverter tray connects through
J5, the IF input jack located on the rear panel. The signal connects to the
First Conversion board and is converted to a second IF of 1044 MHz by an
image rejection mixer located on the First Conversion board. A filter
selects the appropriate conversion product, which is then amplified to a
level of approximately –8 dBm. The 1 GHz LO frequency is generated
externally by the Axciter modulator and is applied to a high pass and low
pass filter designed to eliminate any other interfering signals that might
be coupled into the 1 GHz LO. The LO is applied to an ALC circuit that
maintains the LO level to each mixer of +13 dBm over a wide range of 1
GHz LO input levels. The LO sample is also sent to the Downconverter
board inside the tray or to the external Downconverter module for its use.
This second IF signal is then applied to a second mixer mounted on the
Final Conversion board that converts it back to a broadcast channel (2-69)
by an LO that operates in 1.0 MHz steps between 1.1-1.9 GHz depending
on the channel selected. The LO frequency equals the Channel center
frequency plus 1044 MHz. (As an example CH: 14: Center Frequency is
473.00 MHz therefore LO2 is 473 + 1044, which equals 1517.00 MHz.)
The output of the mixer is applied to a 900 MHz Low pass filter to remove
unwanted conversion products. The resulting signal is amplified and wired
to a Pin diode attenuator and then connected to the output of the
Upconverter/Downconverter Tray or the output of the Upconverter
Module. This pin diode attenuator adjusts the gain of the tray or module