User's Manual

Innovator CU5-1800BTD/BRD ATSC Transmitter/ Board Descriptions
Regenerative Translator
Instruction Manual, Rev. 0 44
before it is applied to the rest of the board as +12VQ and +12VI. The -12 VDC SYS
connects to J19A, B & C and to regulator circuit. The -12V SYS is filtered by L6, L7, C111
and C112 before it is applied to the rest of the board as -12VI and –12VQ.
The +12V SYS also connects through the resistor R81 to provide +5V EXT to the rest of
the board, and to the regulators U23 that provides +3.3V to the rest of the board and to
U27 that provides +1.8V output. The +3.3V also connects to U24 that supplies +1.5V
output. The +12V SYS connects to the regulator U25 and U26 to supply the +5VA output.
The output of U25 also connects to U28, which provides the +5V output to the rest of the
board. +12V SYS is filtered by L4 and C107 to provide the +12V output to the board.
The –12V SYS also connects to the regulator U22 that provides the –5V VA to the rest of
the board. -12V SYS is filtered by L5 and C108 to provide the -12V output to the board.
J2
IF Input
0 dBm Pk Pwr
Pin
Attenuator
In Phase In Phase
Splitter
Quad Quad Quad
Combiner
Amplitude and Phase Correction
Input and
Modulation
Detectors
Input Fault
Indicator
Video Loss
Indicator
Front Panel
ALC
Input
Fault
Modulation
Loss
Level
Detector
TP1 = 1V
Frequency
Response
Corrector
Frequency
Response
Corrector
Frequency
Response
Corrector
J1
IF
Output
(A3) IF Pre-Corrector Board (1308796)
The IF Pre-Corrector Board provides ALC, automatic or manual, gain control of the IF
level. The board also supplies pre-correction Response, In Phase and Quadrature Non-
Linear adjustments. The board has the circuitry for ALC Fault, Input Fault and
Modulation Fault monitoring and indications.
The input IF signal at J2, typically 0 dBm peak power centered at 36 or 44 MHz, is fed to a
splitter circuit Z1 which produces two equal outputs, one at Port 1 and the other at Port 2.
The output at Port 1 connects to the input and modulation fault circuitry. The output at
Port 2 connects to the pin-diode attenuator circuit.
Pin-Diode Attenuator Circuit
The output of Z1 at Port 2 connects to a pin-diode attenuator circuit that consists of CR1,
CR2 & CR3. Each of the pin diodes contains a wide intrinsic region; this makes the diodes
function as voltage-variable resistors at this intermediate frequency. The value of the
resistance is controlled by the DC bias supplied to the diode. The pin diodes are
configured in a pi-type attenuator configuration where CR1 is the first shunt element, CR3
is the series element, and CR2 is the second shunt element. The control voltage, which
can be measured at TP2, originates either from the ALC circuit when the switch S1 is in