System Description Chapter 2

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10-kW UHF Transmitter with Chapter 2, System Description

Feedforward Driver

840A, Rev. 0 2-1

Chapter 2

System Description

The 840A (1064941) is a complete 10-

kW UHF internally diplexed television

transmitter that operates at a nominal

visual output power of 10,000 watts peak

sync visual and an average aural output

power of 1000 watts with a 10 dB

aural/visual ratio.

2.1 System Overview

The 840A is made up of three cabinet

assemblies: the (A1) dual 250-watt

driver/amplifier assembly (1064946);

(A2) the 10-kW amplifier assembly

(1299-1100); and (A3) the high-voltage

power supply assembly, 208/240 VAC

(1068022).

2.1.1 (A1) Dual 250-Watt

Exciter/Amplifier Assembly

(1064946; Appendix A)

The dual 250-watt driver/amplifier

assembly is made up of the assemblies

and trays shown in Table 2-1.

Table 2-1. Driver/Amplifier Assembly Assemblies and Trays

DESIGNATION NUMBER TRAY/ASSEMBLY NAME DRAWING NUMBER

A2 AC distribution assembly 1265-1600

A4 UHF exciter tray 1063301

A9 3-watt amplifier tray 1068203

A6 and A7 250-watt amplifier trays

1044027, low-band;

1044028, mid-band;

1044029, high-band

A14 Bandpass filter assembly --

The exciter/amplifier assembly

(1064946) is connected to the baseband

video and aural inputs. The assembly

also provides connections for the remote

monitoring and operation of the

exciter/amplifier assembly. The UHF

exciter tray (1063301) takes the

baseband aural and video inputs and

produces the visual and aural RF signals

on the channel frequencies. The

combined visual and aural RF output (+7

dBm) of the exciter feeds the 3-watt

amplifier tray (1068203). The 3-watt

amplifier tray contains an automatic gain

control circuit and two 3-watt amplifier

boards. The tray generates the output

level needed to drive the 250-watt

amplifier trays (1044027, low-band;

1044028, mid-band; and 1044029, high-

band).

The output from the 3-watt tray is fed to

the (A10) RF hybrid splitter SMA

connection J1. The RF hybrid splitter

output feeds the RF signal to one of the

250-watt amplifiers directly and, through

(A5) the line stretcher, to the other 250-

watt amplifier. The line stretcher gives

the operator the ability to control the

phase of the output signal that is fed to

one of the 250-watt trays. Each of the

250-watt amplifier trays contains an

amplifier enclosure and feedforward

circuits to achieve an output of 250-watts

peak visual power and 25 watts of aural

power.

In the 250-watt amplifier tray, a forward

power sample from the UHF coupler is

connected to the dual peak detector

board; this board provides a peak-

detected forward sample to the amplifier

control board for metering purposes.

Before exiting the 250-watt amplifier

tray, the RF is fed through a circulator for

the protection of the tray from high

VSWR conditions. The reject port of the

circulator is cabled to the reject

Summary of content (18 pages)

PAGE 1
0-kW UHF Transmitter with Feedforward Driver Chapter 2, System Description Chapter 2 System Description The 840A (1064941) is a complete 10kW UHF internally diplexed television transmitter that operates at a nominal visual output power of 10,000 watts peak sync visual and an average aural output power of 1000 watts with a 10 dB aural/visual ratio. 2.
PAGE 2
10-kW UHF Transmitter with Feedforward Driver load/coupler board; this board supplies the reflected sample to the dual peak detector board, single supply. This signal is then sent to the amplifier control board for metering purposes.
PAGE 3
10-kW UHF Transmitter with Feedforward Driver two separate power supplies: the control power supply and the bias power supply. The control power supply produces the ±12 VDC to the metering circuits (peak detectors) in the 10-kW amplifier as well as the fault sensing boards, differential buffer boards, and control logic boards in the metering control panel. The bias power supply produces the -80 VDC bias voltage to the tube. R1, the bias voltage adjustment, is located behind the metering control panel.
PAGE 4
10-kW UHF Transmitter with Feedforward Driver output metering. It also contains (A2) a visual/aural metering board (1161-1103 or 1161-1115) for aural output and visual output power levels and reflected power levels for VSWR protection. Chapter 2, System Description 2.2 Control and Status Information on the control and status of this system is provided by control, status, and LED indicators and meters on the front panel of the trays.
PAGE 5
10-kW UHF Transmitter with Feedforward Driver Chapter 2, System Description Table 2-3. UHF Exciter Tray Control Switches SWITCH Transmitter (S1) Operate/Standby Mode Select (S2) Auto/Manual Power Adjust (R1) FUNCTION The momentary switch (S1) applies a ground to K1, a latching relay on the transmitter control board. K1 will switch either to Operate or to Standby, depending on which direction S1 is pushed. When switched to Operate, the low Enable commands are applied to the four UHF amplifier trays.
PAGE 6
10-kW UHF Transmitter with Feedforward Driver Chapter 2, System Description Table 2-5.
PAGE 7
10-kW UHF Transmitter with Feedforward Driver Chapter 2, System Description 2.2.3 250-Watt Amplifier Trays Table 2-8. 250-Watt Amplifier Tray Meters METER Meter (A12) FUNCTION Reads power in terms of a percent of the calibrated power output value. A full-scale reading is 100%, which is equivalent to the full-rated 250 watts peak of sync visual + aural output power. Also reads % Reflected Power, power supply voltage levels, and AGC voltage levels.
PAGE 8
10-kW UHF Transmitter with Feedforward Driver Chapter 2, System Description 2.2.4 10-kW Amplifier Assembly Metering Control Panel Table 2-10. 10-kW Amplifier Assembly Meters METER Voltage Meter (M1) Current Meter (M2) 840A, Rev. 0 FUNCTION Reads DC voltage (a full-scale reading is 1 volt) Note: A multiplier, whose value is dependent on which position switch S1 is in, must be applied. The multiplier that is needed is marked in parentheses near the switch.
PAGE 9
10-kW UHF Transmitter with Feedforward Driver METER Power Meter (M3) Chapter 2, System Description FUNCTION Reads power in terms of a percent of the calibrated power value (a full-scale reading will be 100%) With Switch S4 in Display Position Selects the desired visual output power, aural output Switch (S4), Power Meter power and the reflected output power readings Reads the visual output power of the Visual Output 10-kW amplifier (100%) Reads the aural output power of the Aural Output 10-kW amplifier (1
PAGE 10
-kW UHF Transmitter with Feedforward Driver SWITCH HV (High Voltage) (S7) Enable/Disable Output Power (S8) Fault Reset (S9) Driver Mode (S10) Normal/Test 840A, Rev. 0 Chapter 2, System Description FUNCTION turn-on sequence with the operator using the front panel controls or remote control. When the switch is enabled (Up), the magnetic latching relay (K1) on (A1) the control logic board will engage. The highvoltage enable indicator will light along with the High-Voltage Request LED.
PAGE 11
10-kW UHF Transmitter with Feedforward Driver Note: The circuit breakers discussed in Table 2-12 are on the AC distribution panel of the 10-kW amplifier and the high-voltage power supply assembly. For the other circuit breakers on the panel to operate, the main AC and the control circuit breakers must both be switched on.
PAGE 12
10-kW UHF Transmitter with Feedforward Driver STATUS INDICATOR Screen (DS12) RF Request (DS13) Chapter 2, System Description FUNCTION step-start and high-voltage contactors. When the main AC and HV circuit breakers are turned on, 208/240 VAC is applied to the transformer of the high-voltage power supply. Indicates that the high voltage (plate voltage) is on and the Screen On command (Enable) has been given to the isolation relay (A7) mounted in the screen power supply assembly.
PAGE 13
10-kW UHF Transmitter with Feedforward Driver Chapter 2, System Description Table 2-14. 10-kW Amplifier Assembly Fault Indicators FAULT INDICATOR Over Temp (DS22) VSWR Cutback (DS23) 840A, Rev. 0 FUNCTION Indicates that the air temperature in the exhaust stack is above 200° F as sensed by the thermal switch (A15-S1) mounted there. When this fault occurs, the voltages will be immediately removed from the tube, but the blower will continue running to cool the transmitter.
PAGE 14
10-kW UHF Transmitter with Feedforward Driver Chapter 2, System Description 2.3 Remote Control Interface Connections The remote control interface connections for the 840A transmitter are listed in the following tables. Table 2-15.
PAGE 15
10-kW UHF Transmitter with Feedforward Driver FUNCTION Chapter 2, System Description REMOTE JACK/PIN NUMBER INTERFACE TYPE Remote Commands Operate Cmd Operate/Standby Cmd Rtn Standby Cmd J5-1 J5-2 J5-3 Contact closure Auto Mode Select Cmd Auto/Manual Select Cmd Rtn Manual Select Cmd J5-4 J5-5 J5-6 Contact closure Contact closure H.V. Enable Cmd H.V. Enable/Disable Cmd Rtn H.V.
PAGE 16
10-kW UHF Transmitter with Feedforward Driver FUNCTION Bias Voltage Rtn Chapter 2, System Description REMOTE JACK/PIN NUMBER J6-16 Filament Voltage Metering Filament Voltage Rtn J6-17 J6-18 INTERFACE TYPE 1V full scale at 1 kΩ source resistance Aural Forward Power 1V full scale at 1 kΩ source J6-20 Metering resistance Aural Forward Power Rtn J6-21 Note: The remote control interface connections for the 10-kW amplifier connect to jacks J1, J4, J5, and J6 of (A10) the remote control and cabinet interface
PAGE 17
10-kW UHF Transmitter with Feedforward Driver FUNCTION Modulator Select Rtn (optional) Chapter 2, System Description REMOTE CONTROL/PIN NUMBER INTERFACE TYPE J9-32 Remote Status Indications Transmitter Operate (Enable) Ind Operate/Standby Ind Return Transmitter Standby (Disable) Ind Transmitter Auto Indicator Auto/Manual Indicator Return Transmitter Manual Indicator VSWR Cutback Indicator VSWR Cutback Indicator Return J9-12 50 mA max current sink J9-13 J9-14 J9-18 50 mA max current sink 50 mA max cu
PAGE 18
10-kW UHF Transmitter with Feedforward Driver Chapter 2, System Description Table 2-17.