User's Manual

Innovator CU5-1800BTD/BRD ATSC Transmitter/ Board Descriptions
Regenerative Translator
Instruction Manual, Rev. 0 52
output power of 100 Watts peak, with an amplification factor of approximately 13 dB.
The amplification circuit consists of push-pull amplifier blocks V1 and V2, connected in
parallel, operating in class AB. In order to match the impedance of the transistors to the
characteristic impedance of the input and output sides, matching networks are placed
ahead and behind the amplifier blocks. Transformers Z3 and Z4 at the input to V1 and
V2 and Z5 and Z6 at the output of V1 and V2 serve to balance the input and output
signals. The paralleling circuit is achieved using the 3-dB input coupler Z1 and the
second part of Z1, which is the 3-dB output coupler. The working point settings of the
amplifier circuits are factory implemented by means of the potentiometers R9, R11, and
R12 and should not be altered. The combined output of Z1 connects to the RF output
jack of the board at J2. The output of the amplifier assembly at J2 connects to J1 on
(A7) the output detector board.
(A6) Amplifier Assembly (1312191) – Used in the CU100 & CU125
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 (1310138). The ALC Board (1308570) 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 (1310138)
This board is a UHF LDMOS 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.
The board has a gain of approximately 17 dB, and can operate at an output power of
150 Watts average power DVB, 220 Watts average power ATSC, or 440 Watts Peak Sync
plus sound in analog operation. The transistors are operated in quadrature, with one