User's Manual

Digital ATSC Exciter-Modulator System Chapter 3, Upconverter/Downconverter
Tray or Module Assemblies
Axcera Axciter, Rev. 0 44
CR2, and their associated components. The selected signal is amplified by
U9 and U10, then applied to a high pass filter and finally amplified to a
level of approximately +21 dBm by U11. The output is connected to a low
pass filter to remove any unwanted harmonic content and leaves the
board at J3 at a level of +20 dBm.
First Conversion Board, Axciter (1306759)
This board takes an external 1 GHz LO and filters and adjust its level to
+10 dBm into each of the two mixers used in the image rejection mixer.
The LO is applied to a low pass filter before being connected to an image
rejection mixer consisting of U1, U2, U3 and U7. The 44 MHz IF input is
connected to the board at J5, is applied to a frequency response network
consisting of R87-R89, L20-22, C60-62 and associated components. It
then is applied to the image rejection mixer. This mixer converts the 44
MHz input to an output frequency of 1044 MHz. The output of the mixer is
amplified by U4 and applied to ceramic band pass filter U5. This filter
rejects any LO leakage at 1 GHz and also any unwanted out of band
products. The output of the filter is amplified by U6 and then filtered
before exiting the board at J1.
AGC Control Board, Axciter (1307366)
AGC Control Board, Axciter
This board performs a variety of functions, which include an interface
between the other boards in the upconverter and the rest of the
transmitter. It also has a microcontroller U8, which controls and monitors
the functions of the other boards in the assembly.
The microcontroller communicates via an RS-485 interface with the
transmitter's system control module. It reports any faults and metering
information and receives channel information, which it passes along to the
PLLs on the L-Band PLL Board and the First Conversion Board.
The board also generates various voltages used by the rest of the boards
in the upconverter. U9 converts the +12V input to the board to +20V.
U15 converts +12V to +5V for the on board 10 MHz crystal oscillator.
SW1 DIP SWITCH
ON OFF
1
J22 CPLD
Programming jack
J12 Microcontroller
Programming jack