User's Manual

Innovator CU5-1800BTD/BRD ATSC Transmitter/ Board Descriptions
Regenerative Translator
Instruction Manual, Rev. 0 50
The VSWR cutback circuit is set so that the ALC circuit will start reducing RF drive once
the Reflected power reaches a level of about 6% and will keep reducing the drive to
maintain that level. U8A, U8B and their associated components, diode-or the metering
voltages, which generates this cutback. The forward power is scaled to 2V = 100 % and
the reflected power is scaled to 2V = 25%. The Reflected metering voltage is doubled
again by U8B so that when the voltage of U8B exceeds the voltage at the output of U8A,
the reflected power takes over the ALC circuit. Once the U8B voltage drops below the
forward power at U8A, the forward power takes over again.
The VSWR shutdown circuit will shut the tray down if the Reflected power increases to
15% or higher, which can happen if the tray sees reflected power when the ALC is in
manual.
The Overdrive protection looks at a sample of the RF signal that is applied to J1 of the
board. The peak level of this signal is detected and can be measured on TP1. This
voltage is applied to a comparator with the threshold set by R38. If this threshold is
exceeded, the ALC circuit mutes then ramps up to try again. This circuit also works in
manual gain as well.
Heatsink
Temperature
Sensor
RF Input
+10 dBm
RF Output
+46 dBm
+32 dBm
(A6) Amplifier Assembly (1309621) – Used in the CU5
The (A6) Amplifier Assembly (1309621) is made up of (A6-A1) the 2 Stage UHF
Amplifier Board, 24V (1309608). The assembly has approximately 33 dB of gain.
(A6-A1) 2 Stage UHF Amplifier Board, 24V (1309608)
The 2 Stage UHF Amplifier Board, 24V (1309608) consists of a driver stage with a gain
of +14dB and two parallel connected final amplifier stages each with a gain of +14dB.
The working point settings for the 2 Stage Amplifier Board are factory set using the
potentiometers R32 for Q2, R15 for Q1, and R24 for Q3 and should not be altered. The
input RF connects to the first amplifier stage Q2. The output is split by U2 and