System Description Chapter 2

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500-Watt VHF Low Band Transmitter Chapter 2, System Description

325A, Rev. 0 2-1

Chapter 2

System Description

The 325A is a complete 500-watt VHF

Low Band solid state internally diplexed

television transmitter that operates at a

nominal visual output power of 500 watts

peak sync and an average aural output

power of 50 watts, at an A/V ratio of 10

dB, 10% sound, or 25 watts at 13 dB,

5% sound.

2.1 System Overview

The 325A (1063850) is made up of the

trays and assemblies listed in Table 2-1.

Table 2-1. 325A Major Trays and Assemblies

MAJOR ASSEMBLY

DESIGNATOR

TRAY/ASSEMBLY NAME DRAWING NUMBER

A2 AC distribution panel 1265-1600

A4 VHF exciter 1070820

A6 and A7 Two VHF amplifier trays 1198-1600

A8 VHF combiner assembly 1198-1010 or 1222-1002

A9 Bandpass filter assembly Channel Determined

A12 Remote interface assembly 1083510

The (A4) VHF exciter can operate using

either the baseband audio and video

inputs alone or, if the (optional) 4.5-MHz

composite input kit is purchased, the 4.5-

MHz composite input or the baseband

video and audio inputs to produce a

diplexed, modulated, and on-channel

frequency visual + aural RF output. The

switching is accomplished by a relay on

the sync tip clamp modulator board that

uses a baseband select to control a relay

that selects either the 4.5 MHz generated

from the baseband inputs or from the

4.5-MHz composite input.

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 from J7-6 and

J7-7. 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 J7-6 and

J7-7.

The RF output of the VHF exciter is split

two ways in (A5) the 2-way power

splitter assembly (ZFSC-2-2). The

outputs of the splitter feed the two (A6

and A7) VHF amplifier trays that amplify

the RF signals to approximately 500

watts each. The outputs of the two VHF

amplifier trays are combined in (A8) the

VHF combiner that provides

approximately 600 watts peak of sync

output. The 600-watt output is connected

to (A9) a bandpass filter assembly. The

bandpass filter is tuned to provide the

high out-of-band rejection of unwanted

products. The filtered signal is connected

to A9-A5, a coupler assembly that

provides a forward and a reflected power

sample to the visual/aural metering

board in the VHF exciter. The forward

sample is processed to provide peak

detected visual and aural power output

samples to the transmitter control board

in the VHF exciter. The reflected power

sample is also peak detected and wired

to the transmitter control board. The

transmitter control board connects the

visual, aural, and reflected power output

samples to the front panel meter to

monitor the system.

Summary of content (10 pages)

PAGE 1
500-Watt VHF Low Band Transmitter Chapter 2, System Description Chapter 2 System Description The 325A is a complete 500-watt VHF Low Band solid state internally diplexed television transmitter that operates at a nominal visual output power of 500 watts peak sync and an average aural output power of 50 watts, at an A/V ratio of 10 dB, 10% sound, or 25 watts at 13 dB, 5% sound. 2.1 System Overview The 325A (1063850) is made up of the trays and assemblies listed in Table 2-1. Table 2-1.
PAGE 2
500-Watt VHF Low Band Transmitter Chapter 2, System Description In the VHF amplifier tray, a forward power sample and a reflected power sample from the 4-way combiner board are connected to the dual peak detector board, single supply, that provides peakdetected forward samples to the amplifier control board that supplies the samples to the front panel meter of the tray.
PAGE 3
500-Watt VHF Low Band Transmitter Chapter 2, System Description 2.2.1 VHF Exciter Tray Table 2-2. VHF Exciter Tray Meters METER Meter (A4-A18) 325A, Rev. 0 FUNCTION This meter reads power in terms of a percentage of the calibrated output power level on the upper scale. The voltage level or frequency level is read on one of the bottom two scales. A full-scale reading on the top scale is 120%. 100% is equivalent to the full-rated 500 watts peak of sync visual.
PAGE 4
500-Watt VHF Low Band Transmitter Chapter 2, System Description Table 2-3. VHF Exciter Tray 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 two VHF amplifier trays.
PAGE 5
00-Watt VHF Low Band Transmitter Chapter 2, System Description Table 2-5. VHF Exciter Tray Samples SAMPLE f(IF) f(IC) f(s) Exciter O/P Transmitter O/P 325A, Rev. 0 DESCRIPTION A sample of the visual IF that is taken from the sample jack on the IF carrier oven oscillator board. A sample of the intercarrier signal that is taken from the sample jack on the aural IF synthesizer board. A sample of the channel oscillator output that is taken from the sample jack of the channel oscillator assembly.
PAGE 6
500-Watt VHF Low Band Transmitter Chapter 2, System Description 2.2.2 VHF Amplifier Tray Table 2-6. VHF Amplifier Tray Switches SWITCH On/Off Circuit Breaker CB1 Switch S1, Meter Switch S2, Meter 325A, Rev. 0 FUNCTION Switches 220 VAC through a 15-amp circuit breaker-type protection device. The switch lights if AC is present. The AC is applied to the switching power supply in the tray.
PAGE 7
500-Watt VHF Low Band Transmitter Chapter 2, System Description Table 2-7. VHF Amplifier Tray Fault Indicators INDICATOR Overdrive (DS1) Enable (DS2) Module Status (DS3) VSWR Cutback (DS4) Overtemp (DS5) DESCRIPTION Indicates that the level of drive is too high. The protection circuit will limit the drive level to the set threshold. The fault is generated on the overdrive protection board.
PAGE 8
500-Watt VHF Low Band Transmitter Chapter 2, System Description The remote connections listed in Table 210 are made to the (A12) A/V input and remote interface assembly. The remote connections are made to jacks J9 and J10 on the assembly. Refer to the interconnect drawing (1076203) for the proper pin remote connections. Table 2-10.
PAGE 9
500-Watt VHF Low Band Transmitter FUNCTION Chapter 2, System Description REMOTE JACK/PIN NUMBER Auto/Manual Indicator Return Transmitter Manual Indicator INTERFACE TYPE J9-19 50 mA max current sink J9-20 VSWR Cutback Indicator 50 mA max current sink J9-23 VSWR Cutback Indicator Return J9-24 Video Loss (Fault) Indicator Video Loss (Fault) Ind. Rtn.
PAGE 10
500-Watt VHF Low Band Transmitter Chapter 2, System Description Table 2-11. VHF Amplifier Tray Remote Interface Connections with the A/V Input and Remote Interface Assembly FUNCTION REMOTE JACK/PIN NUMBER Forward Output Power (A6) VHF Amp Forward Output Power (A6) Rtn Reflected O/P Power (A6) VHF Amp Reflected O/P Power (A6) Rtn Forward Output Power (A7) VHF Amp Forward Output Power (A7) Rtn Reflected O/P Power (A7) VHF Amp Reflected O/P Power (A7) Rtn 2.