System Description Chapter 2

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100 Watt High Band VHF Transmitter Chapter 2, System Description

420A, Rev. 0 2-1

Chapter 2

System Description

The 420A is a complete 100 watt high

band VHF solid-state internally diplexed

television transmitter that operates at a

nominal visual output power of 100 watts

peak sync and an average aural output

power of 10 watts at a 10 dB A/V

ratio,10% sound.

The 420A has been submitted for type

acceptance to the FCC; the relevant FCC

identifier for the 420A is

_________________.

2.1 420A System Overview

The 420A (1066428) consists of (A1) a

100-watt, high-band VHF

exciter/amplifier tray (1066308) and (A2)

a bandpass filter assembly.

The exciter/modulator section of the 100-

watt, high-band VHF exciter/amplifier

tray operates using either baseband

audio and video inputs. However, if the

(optional) 4.5 MHz composite input kit

(1273-1128) is purchased, the 4.5 MHz

composite input or the baseband video

and audio inputs are used to produce a

diplexed, modulated, on-channel

frequency visual + aural RF output. The

switching between the 4.5 MHz

generated by the baseband inputs or by

the 4.5 MHz composite input is

accomplished by a relay, on the sync tip

clamp modulator board. The relay is

controlled by a baseband select which

connects to J18-6 and 7 on the rear of

the tray. To operate the transmitter with

the (optional) 4.5 MHz composite input

kit using baseband inputs, the baseband

video must be connected to J1 or J2, the

baseband audio must be connected to

the proper input jack, and a baseband

select must be connected to J18-6 and 7.

To operate the transmitter with the

(optional) 4.5 MHz composite input kit

using the 4.5 MHz composite input, the

4.5 MHz composite input must be

connected to J1 or J2 and the baseband

select must be removed from J18-6 and

The exciter/modulator section of the tray

takes the baseband audio and video

inputs, or the (optional) 4.5 MHz

composite input, and produces a

combined 45.75 MHz + 41.25 MHz IF

output that connects to J32 on the ALC

board. The combined IF output of the

ALC board connects to the

mixer/amplifier assembly where it is

upconverted and filtered to the on-

channel frequency visual + aural RF

output. The RF is filtered and amplified in

the amplifier section to the 100-watt

output power level. The RF output is

filtered in the bandpass filter assembly

and fed to the antenna via the

transmission line.

The exciter and upconverter section of

the tray operate when the circuit breaker

CB1 is on, but the amplifier section only

operates when the transmitter is in

Operate. This occurs because the

switching power supply that supplies the

operating voltages to the amplifier

section has an inhibit command applied

to it, shutting it off as long as the

transmitter is in Standby.

2.1.1 Exciter Section

The baseband video and audio inputs to

the transmitter connect to the rear panel

of the tray. The baseband video or the

(optional) 4.5 MHz composite input

connects to jack (J2), which is a loop-

through connected to jack (J1). By

removing the termination jumper on the

sync tip clamp/modulator board, jack

(J1) can be used as a connection for the

baseband video or the 4.5 MHz

composite input to another transmitter.

The baseband audio input connects to

the terminal block (TB1) for balanced

Summary of content (9 pages)

PAGE 1
00 Watt High Band VHF Transmitter Chapter 2, System Description Chapter 2 System Description The 420A is a complete 100 watt high band VHF solid-state internally diplexed television transmitter that operates at a nominal visual output power of 100 watts peak sync and an average aural output power of 10 watts at a 10 dB A/V ratio,10% sound. The 420A has been submitted for type acceptance to the FCC; the relevant FCC identifier for the 420A is _________________. 2.
PAGE 2
100 Watt High Band VHF Transmitter audio or to the BNC jack (J3) for composite audio, which is a loop-through connected to jack (J13). There are also connections for the remote monitoring and operation of the transmitter at the "D"-connector jacks (J10 and J11). The baseband audio connects to (A4) the aural IF synthesizer board (1265-1303), in the exciter section, which provides the amplification for each of the three possible audio inputs and the amplifier circuit that supplies the single audio output.
PAGE 3
100 Watt High Band VHF Transmitter A5) 2-way combiner board. The RF output from the 2-way combiner board (+51 dBm) is fed through (A31) an output coupler board (1088-1104) that provides a forward power sample to (A19) the visual/aural metering board (1265-1309). A forward sample connects to the transmitter control board that supplies the voltage sample to the front panel meter of the tray. The reject port of the output coupler board provides the reject sample to the visual/aural metering board.
PAGE 4
100 Watt High Band VHF Transmitter 2.1.7 Control and Status Chapter 2, System Description Meters, switches, and LED indicators are mounted on (A17) the transmitter control board (1068933). The control board is attached to the back of the front panel to allow for the switches and the LEDs to be operated or viewed from the front of the tray.
PAGE 5
100 Watt High Band VHF Transmitter Chapter 2, System Description Table 2-1. Meters METER METER (A18) (mounted on the front panel) SWITCH (S3), METER (mounted on the front panel) ALC (0-1 V) % EXCITER (0-120) % REFLECTED (0-120) % VISUAL POWER (0-120) % AURAL POWER (0-120) VIDEO (0-1V) AUDIO (0-100kHz) 420A, Rev. 0 FUNCTION Displays power in terms of a percentage of the calibrated output power level. A fullscale reading is 120%.
PAGE 6
100 Watt High Band VHF Transmitter Chapter 2, System Description Table 2-2. Switches (mounted on the front panel) SWITCH TRANSMITTER (S1) OPERATE/STANDBY MODE SELECT (S2) AUTO/MANUAL FUNCTION The momentary contact switch (S1) applies a ground to K1, latching relay, located 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 inhibit command is removed from the switching power supply.
PAGE 7
100 Watt High Band VHF Transmitter Chapter 2, System Description Table 2-4.
PAGE 8
100 Watt High Band VHF Transmitter Chapter 2, System Description loop-through connected, for composite, stereo, audio. To use the 4.5 MHz composite input kit, the baseband audio can remain connected to the VHF exciter even if the 4.5 MHz composite input kit is used, but the baseband video must be disconnected from J1 or J2 and the 4.5 MHz composite input connected to J1 or J2. The baseband select command must also be removed from J18-6 and 7.
PAGE 9
100 Watt High Band VHF Transmitter Chapter 2, System Description Table 2-7. Remote Interface Connections FUNCTION Modulator Select (optional) Modulator Select Rtn (optional) REMOTE JACK/PIN NUMBER J11-10 INTERFACE TYPE Contact closure J11-30 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 50 mA max. current sink J10-3 J10-16 50 mA max.