User's Manual

Innovator CU0TD-1/CU0RD-1 – CU4TD/CU4RD ATSC Board Descriptions
Transmitter/Regenerative Translator
Instruction Manual, Rev. 2 113
The bias voltage for the transistor is generated from +48VDC that connects through the
resistor R3 to the drain on Q1 and through the voltage regulator U1. The regulated
voltage at the output of U1 is adjusted with the pots R7 and R6 before it is connected to
the drain on Q1. The Diode CR1 provides temperature compensation for the transistor.
The transistor is capable of producing an output of over 20 Watts ATSC. The amplified
output is connected thru a matching network to one input of U4 a hybrid combiner.
The other output of the input splitter is fed thru an identical amplifier circuit as described
for the Q1 transistor, except it is for the Q2 transistor. C45 is adjustable for best
response, R16 and R17 are the bias adjustment pots and CR2 is the temperature
compensating diode for the Q2 amplifier circuit. The amplified output of Q2 is connected
thru a matching network to the other input of the U4 hybrid combiner. The hybrid
combiner combines the two amplified outputs of the Q1 and Q2 LDMOS devices and
produces a single RF output (≈+42dBm) of the board and the assembly, which a cabled
to the (A12) Coupler Board.
(A6) Amplifier Assembly (1312191) – Used in CU0TD/RD-4 & CU0TD/RD-5
The (A6) Amplifier Assembly (1312191) is made up of (A6-A1) the 1 Watt Amplifier
Board (1310282), (A6-A2) the BL871 Single Stage Amplifier Board (1311041), and (A6-
A3) the Dual 878 Pallet Assembly (1313170 or 1310138). The ALC Board (1315006) is
also used with this assembly. The entire amplifier assembly has approximately 36 dB of
gain.
(A6-A1) 1 Watt UHF Amplifier Module (1310282)
This board is a broadband UHF amplifier capable of producing an output power in excess
of 1W Peak. It is normally operated at an average power of 100 mW 8VSB or lower. It
consists of two AH202 MMICs operating in parallel. The board is powered by +12 VDC
and has no adjustments. The board has a gain of approximately 16 dB.
(A6-A2) BL871 Single Stage Amplifier Board (1311041)
This board consists of a single stage amplifier operating at +42 VDC. The board has an
overall gain of about 16 dB. The input to the board passes through a 3 dB attenuator
consisting of R11-R13, and then is applied to the gain stage, which consists of a single
LDMOS transistor Q1 operating in Class AB. The bias voltage for the transistor is
generated through the voltage regulator U1, and is adjusted using pots R2 and R3. The
Diode CR1 provides temperature compensation for the transistor. The transistor will
output over 20 Watts DVB, but is typically used in a driver application at much lower
output powers. The Directional Coupler U1 provides a 20 dB down sample of the RF
output.
(A6-A3) Dual 878 Pallet Assembly (1313170 or 1310138)
This board is a LDMOS UHF power amplifier consisting of two power transistors
operating in parallel. The board operates on a power supply voltage of +42 VDC. The
voltage regulator U1 steps down the voltage to provide a bias voltage to each transistor.
The diodes CR1 and CR3 are used to temperature compensate the bias voltage. As the
RF transistors heat up, the diodes also heat up, causing the voltage across them to drop,
lowering the bias voltage to the RF transistors so that it remains constant with device
temperature.