User's Manual

Innovator CU5-1800BTD/BRD ATSC Transmitter/ Board Descriptions
Regenerative Translator
Instruction Manual, Rev. 0 49
External 10 MHz reference is present. The Red LED DS3 will light if the PLL for the 10
MHz oscillator is not locked.
Pin AttenuatorJ1
RF Input
Input Loss
Detector
Auto/Man Select
ALC
TP4
Mute from
Control Circuit
J2
RF Output
TP1
Overdrive Detect
Output Power
Reflected Power
Input Power
Reference
(A5) ALC Board, Innovator CX Series (1308570)
The ALC Board, Innovator CX Series, is used to control the RF drive power to the RF
amplifier chain in the CU30, CU50, CU100 and CU125 systems. The board accepts an 8-
VSB RF input signal at a nominal input level of -3 dBm average power and amplifies it to
whatever drive level is necessary to drive the final RF amplifier in the tray to full power.
The input signal to the board at J1 is split by U4, with one half of the signal driving a PIN
diode attenuator, DS1 and DS2, and the other half driving a detector, U13, that is used
to mute the PIN attenuator when there is no input signal. The output of the PIN
attenuator is sent to two cascaded amplifiers, U2 and U3, which are capable of
generating +10 dBm average power from the board at J2.
The PIN attenuator is driven by an ALC circuit or by a manual fixed voltage bias,
depending on the position of switch S1. When the switch is pointing to the left, looking
from the front of the tray, the ALC circuit is enabled. When the switch is pointing to the
right, the ALC circuit is disabled and the PIN attenuator is controlled through the Manual
gain pot R62. When the switch is in either ALC or manual, the voltage in the unused
circuit is preset low by the circuitry connected to pins 4-6 on SW1. This allows the RF
power to ramp up slowly to full power when the switch changes positions. CR8, C33 and
associated components control the ramp up speed of the manual gain circuit. CR9, C42
and their associated circuits do the same thing for the ALC circuit. The practical effect of
this is to preset the RF drive power to near zero output power when enabling and
disabling the ALC, followed by a slow controlled ramp up of power.
The ALC circuit normally attempts to hold the tray output power constant, but there are
four faults that can override this. These faults are Input Fault, VSWR Cutback Fault,
VSWR Shutdown Fault and Overdrive Fault.
The Input Fault is generated by comparator U7C and presets the PIN attenuator and ALC
circuit to maximum attenuation whenever the input signal drops below about -7 dBm.
Test point TP2 allows the user to measure the detected input voltage.