UBS Axcera 325A 500-Watt VHF Low-band Television Transmitter User Manual Chapter 2

UBS-Axcera 500-Watt VHF Low-band Television Transmitter Chapter 2

Chapter 2

500-Watt VHF Low Band Transmitter Chapter 2, System Description325A, Rev. 0 2-1Chapter 2System DescriptionThe 325A is a complete 500-watt VHFLow Band solid state internally diplexedtelevision transmitter that operates at anominal visual output power of 500 wattspeak sync and an average aural outputpower of 50 watts, at an A/V ratio of 10dB, 10% sound, or 25 watts at 13 dB,5% sound.2.1 System OverviewThe 325A (1063850) is made up of thetrays and assemblies listed in Table 2-1.Table 2-1. 325A Major Trays and AssembliesMAJOR ASSEMBLYDESIGNATOR TRAY/ASSEMBLY NAME DRAWING NUMBERA2 AC distribution panel 1265-1600A4 VHF exciter 1070820A6 and A7 Two VHF amplifier trays 1198-1600A8 VHF combiner assembly 1198-1010 or 1222-1002A9 Bandpass filter assembly Channel DeterminedA12 Remote interface assembly 1083510The (A4) VHF exciter can operate usingeither the baseband audio and videoinputs alone or, if the (optional) 4.5-MHzcomposite input kit is purchased, the 4.5-MHz composite input or the basebandvideo and audio inputs to produce adiplexed, modulated, and on-channelfrequency visual + aural RF output. Theswitching is accomplished by a relay onthe sync tip clamp modulator board thatuses a baseband select to control a relaythat selects either the 4.5 MHz generatedfrom the baseband inputs or from the4.5-MHz composite input.To operate the transmitter with the(optional) 4.5-MHz composite input kitusing baseband inputs, the basebandvideo must be connected to J1 or J2, thebaseband audio must be connected tothe proper input jack, and a basebandselect must be connected from J7-6 andJ7-7. To operate the transmitter with the(optional) 4.5-MHz composite input kitusing the 4.5-MHz composite input, the4.5-MHz composite input must beconnected to J1 or J2 and the basebandselect must be removed from J7-6 andJ7-7.The RF output of the VHF exciter is splittwo ways in (A5) the 2-way powersplitter assembly (ZFSC-2-2). Theoutputs of the splitter feed the two (A6and A7) VHF amplifier trays that amplifythe RF signals to approximately 500watts each. The outputs of the two VHFamplifier trays are combined in (A8) theVHF combiner that providesapproximately 600 watts peak of syncoutput. The 600-watt output is connectedto (A9) a bandpass filter assembly. Thebandpass filter is tuned to provide thehigh out-of-band rejection of unwantedproducts. The filtered signal is connectedto A9-A5, a coupler assembly thatprovides a forward and a reflected powersample to the visual/aural meteringboard in the VHF exciter. The forwardsample is processed to provide peakdetected visual and aural power outputsamples to the transmitter control boardin the VHF exciter. The reflected powersample is also peak detected and wiredto the transmitter control board. Thetransmitter control board connects thevisual, aural, and reflected power outputsamples to the front panel meter tomonitor the system.
500-Watt VHF Low Band Transmitter Chapter 2, System Description325A, Rev. 0 2-2In the VHF amplifier tray, a forwardpower sample and a reflected powersample from the 4-way combiner boardare connected to the dual peak detectorboard, single supply, that provides peak-detected forward samples to the amplifiercontrol board that supplies the samplesto the front panel meter of the tray.2.2 Control and StatusControl and status information for thetransmitter is provided by the meter andLED indicators on the front panel of theVHF exciter. The switches and LEDindicators are part of the (A17)transmitter control board that is mountedso that the switches and LEDs areoperated or viewed from the front panelof the VHF exciter.Switch S1 is an Operate/Standby switchthat controls the output of thetransmitter by providing the Enablesthat, when the transmitter is in Operate,are needed to turn on the switchingpower supplies in the two VHF amplifiertrays. In Operate, the green LED DS2 ison and in Standby the amber LED DS1 ison. If the transmitter does not switch toOperate when S1 is switched to Operate,check that a dummy jumper plug, with ajumper between pins 23 and 24, isconnected to jack J11 on the back of thetray. The jumper plug must be connectedto (A12-J9) when the (optional) remoteinterface panel is used. This jumperprovides the interlock needed for thetransmitter to operate. If the interlock ispresent, the green LED DS5 should be lit.Switch S2 is an Automatic/Manual switchthat controls the operation of thetransmitter by the presence of the videoinput signal. When the switch is inAutomatic, the green LED DS3 is lit and,if the video input signal to thetransmitter is lost, the transmitter willautomatically switch to Standby. Whenthe video input signal returns, thetransmitter will automatically switch backto Operate. In Manual, the amber LEDDS4 is lit and the operation of thetransmitter is controlled by the frontpanel switches. During normal operationof the transmitter, switch S2 should be inthe Auto position. The front panel of theVHF exciter also has LEDs that indicate aVideo Fault (Loss; red LED DS9) andVSWR Cutback (amber LED DS7).
500-Watt VHF Low Band Transmitter Chapter 2, System Description325A, Rev. 0 2-32.2.1 VHF Exciter TrayTable 2-2. VHF Exciter Tray MetersMETER FUNCTIONThis meter reads power in terms of a percentage of thecalibrated output power level on the upper scale. Thevoltage level or frequency level is read on one of the bottomtwo scales. A full-scale reading on the top scale is 120%.100% is equivalent to the full-rated 500 watts peak ofsync visual. The meter also reads % Aural Power, % ExciterPower, % Reflected Power, audio levels, video levels, andthe ALC reading.With Switch S3 inPosition DisplaySwitch S3, MeterSelects the desired ALC voltagereading, % Exciter Power, %Reflected Power, % VisualPower, % Aural Power, videolevel, or audio level.Audio(0 to 100 kHz)Reads the audio level, ±25 kHzbalanced or ±75 kH composite,on the 0 to 10 scale. Willindicate baseband audio, if it isconnected to the transmitter,even with the video + 4.5-MHzSCA input selected.ALC(0 to 10 volts) Reads the ALC voltage level, .8VDC, on the 0 to 10 scale.% Exciter(0 to 120)Reads the % Exciter OutputPower Level needed to attain100% output of the transmitteron the top scale.% Aural Power(0 to 120)Reads the % Aural OutputPower of the transmitter,100% = 100 watts at 10 dBA/V ratio, on the top scale.% Visual Power(0 to 120)Reads the % Visual OutputPower of the transmitter,100% = 500 watts peak ofsync, on the top scale.% Reflected(0 to 120) Reads the % Reflected OutputPower, <5%, on the top scale.Meter (A4-A18)Video(0 to 1 volt) Reads the video level, at white,on the bottom 0 to 10 scale.
500-Watt VHF Low Band Transmitter Chapter 2, System Description325A, Rev. 0 2-4Table 2-3. VHF Exciter Tray SwitchesSWITCH FUNCTIONTransmitter S1Operate/StandbyThe momentary switch S1 applies a groundto K1, a latching relay on the transmittercontrol board. K1 will switch either toOperate or to Standby depending on whichdirection S1 is pushed. When switched toOperate, the low, Enable commands areapplied to the two VHF amplifier trays.These Enables will turn on the VHF amplifiertrays. The opposite occurs when the switchis turned to Standby.Mode Select S2Auto/ManualThe momentary switch S2 applies a groundto K2, a latching relay on the transmittercontrol board. K2 will switch the transmitterto Automatic or Manual depending on whichdirection S2 is pushed. In Automatic, thevideo fault command from the ALC Boardwill control the operation of the transmitter.The transmitter will switch to Standby, aftera slight delay, if the input video is lost andwill switch back to Operate, quickly, whenthe video is restored. In Manual, thetransmitter is controlled by the operatorusing the front panel Operate/Standbyswitch or by remote control.Power Adjust (R1) The 5 kΩ pot A20 sets the ALC level on theALC board to set the output power of thetransmitter.Table 2-4. VHF Exciter Tray Fault IndicatorsINDICATOR DESCRIPTIONVideo Loss (DS9 Red)Indicates that the input video to thetransmitter has been lost. The fault isgenerated on the ALC board in the VHFexciter tray.VSWR Cutback (DS7 Amber)Indicates that the reflected power level ofthe transmitter has increased above 20%;this automatically cuts back the outputpower level to 20%. The fault is generatedon the transmitter control board in the VHFexciter tray.
500-Watt VHF Low Band Transmitter Chapter 2, System Description325A, Rev. 0 2-5Table 2-5. VHF Exciter Tray SamplesSAMPLE DESCRIPTIONf(IF) A sample of the visual IF that is taken fromthe sample jack on the IF carrier ovenoscillator board.f(IC) A sample of the intercarrier signal that istaken from the sample jack on the aural IFsynthesizer board.f(s) A sample of the channel oscillator outputthat is taken from the sample jack of thechannel oscillator assembly.Exciter O/P An output power sample of the exciter thatis taken from the VHF filter/amplifier board.Transmitter O/P A forward power sample of the transmitterthat is taken from the visual/aural meteringboard.
500-Watt VHF Low Band Transmitter Chapter 2, System Description325A, Rev. 0 2-62.2.2 VHF Amplifier TrayTable 2-6. VHF Amplifier Tray SwitchesSWITCH FUNCTIONOn/Off Circuit Breaker CB1 Switches 220 VAC through a 15-amp circuit breaker-typeprotection device. The switch lights if AC is present. The ACis applied to the switching power supply in the tray.Selects the desired % Visual Forward Output Power, %Visual Reflected Power reading, AGC Voltage, Power SupplyVoltage, or CurrentWith Switch S1 inPosition Display% Forward Reads the % Forward OutputPower of the tray (100%= 500watts peak of sync + aural)% Refl (Reflected) Reads the % Reflected OutputPower (<10%)AGC Voltage Reads the AGC level of the tray(1 to 2 VDC)Power Supply Reads the voltage from theswitching power supply (+48VDC)Switch S1, MeterCurrent Uses Switch S2 to indicate thecurrent of transistor devicesSelects the current of the transistor devices on the highband amplifier boards. S1 must be in the Current position.With Switch S2 inPosition DisplayI1Reads the current of (A3-A1)the low band amplifier board(idling current=2 amps andoperating current=5 amps)I2Reads the current of (A3-A2)the low band amplifier board(idling current=2 amps andoperating current=5 amps)I3Reads the current of (A3-A3)the low band amplifier board(idling current=2 amps andoperating current=5 amps)Switch S2, MeterIDReads the current of (A2-A1)the low band amplifier board(idling current=3 amps andoperating current=3-4 amps)
500-Watt VHF Low Band Transmitter Chapter 2, System Description325A, Rev. 0 2-7Table 2-7. VHF Amplifier Tray Fault IndicatorsINDICATOR DESCRIPTIONOverdrive (DS1)Indicates that the level of drive is too high.The protection circuit will limit the drivelevel to the set threshold. The fault isgenerated on the overdrive protectionboard.Enable (DS2) Indicates that the Enable supplied by theexciter tray is presentModule Status (DS3) Indicates that the forward power samplelevel is lower than the set reference levelVSWR Cutback (DS4)Indicates that the reflected level of thetray has increased above 20%; this willautomatically cut back the output power ofthe tray. The fault is generated on theAGC control board.Overtemp (DS5)Indicates that the temperature of (A13,A14 or A15) one of the thermal switches isabove 80° C. When this fault occurs, theEnable to the switching power supply isimmediately removed.Table 2-8. VHF Amplifier Tray Control AdjustmentsADJUSTMENT DESCRIPTIONPhase (A7-R2) Adjusts the phase of the RF output byapproximately 70%Gain (A6-R3) Adjusts the gain of the RF output when theamplifier control board is in the AGC modeTable 2-9. VHF Amplifier Tray SampleSAMPLE DESCRIPTIONRF Front Panel Sample Forward power sample of the tray from theAGC control board2.3 Input and Remote ConnectionsThe baseband video and audio inputsalone or, if the (optional) 4.5-MHzcomposite input kit is purchased, the 4.5-MHz composite input or the basebandvideo input and audio input to thetransmitter, connect to the rear of theVHF exciter tray. The baseband videoinput or the 4.5-MHz composite inputconnects to jacks J1 or J2, which areloop-through connected. The basebandaudio input connects to TB1 for balancedaudio or to jacks J3 or J13, which areloop-through connected, for composite,stereo, audio. To use the 4.5-MHzcomposite input kit, the baseband audiocan remain connected to the VHF excitereven if the 4.5-MHz composite input kit isused, but the baseband video must bedisconnected from J1 or J2 and the 4.5-MHz composite input must be connectedto J1 or J2. The baseband selectcommand must be removed from J7-6and J7-7.
500-Watt VHF Low Band Transmitter Chapter 2, System Description325A, Rev. 0 2-8The remote connections listed in Table 2-10 are made to the (A12) A/V input andremote interface assembly. The remoteconnections are made to jacks J9 and J10on the assembly. Refer to theinterconnect drawing (1076203) for theproper pin remote connections.Table 2-10. VHF Exciter Remote Interface Connections with the A/V Input and Remote Interface AssemblyFUNCTION REMOTE JACK/PINNUMBER INTERFACE TYPETransmitter Enable Interlock J9-21Transmitter Enable InterlockRtn. J9-22J9-21 and J9-22 must bejumpered together fornormal operation. The(1176-1038) jumper jackshould be used.Remote Control CommandsTransmitter Standby(Disable) J9-9 Contact closureTransmitterStandby/Operate Rtn. J9-10Transmitter Operate(Enable) J9-11 Contact closureTransmitter Manual J9-15 Contact closureTransmitter Auto/ManualRtn. J9-16Transmitter Auto J9-17 Contact closurePower Level Raise (Optional) J9-27 Contact closurePwr Lvl Raise/Lower Rtn(Optional) J9-28Power Level Lower(Optional) J9-29 Contact closureModulator Select (Optional) J9-31 Contact closureModulator Select Rtn(Optional) J9-32Remote Status IndicationsTransmitter Operate(Enable) Ind. J9-12 50 mA max current sinkOperate/Standby Ind.Return J9-13Transmitter Standby(Disable) Ind. J9-14 50 mA max current sinkTransmitter Auto Indicator J9-18 50 mA max current sink
500-Watt VHF Low Band Transmitter Chapter 2, System Description325A, Rev. 0 2-9FUNCTION REMOTE JACK/PINNUMBER INTERFACE TYPEAuto/Manual IndicatorReturn J9-19Transmitter ManualIndicator J9-20 50 mA max current sinkVSWR Cutback Indicator J9-23 50 mA max current sinkVSWR Cutback IndicatorReturn J9-24Video Loss (Fault) Indicator J9-25 50 mA max current sinkVideo Loss (Fault) Ind. Rtn. J9-26Receiver Fault (Optional) J9-30Remote MeteringVisual Output Power J9-1Visual Output Power Rtn J9-2 1V full scale at 1kΩ sourceresistanceAural Output Power J9-3Aural Output Power Rtn J9-4 1V full scale at 1kΩ sourceresistanceReflected Power J9-5Reflected Power Rtn J9-6 1V full scale at 1kΩ sourceresistanceExciter Output Power J9-7Exciter Output Power Rtn J9-8 1V full scale at 1kΩ sourceresistanceThe remote connections shown in Table2-11 are made to the (A12) A/V inputand remote interface assembly. Theseremote connections are made to jacks J9and J10 on the assembly. Refer to theinterconnect drawing (1076203) for theproper pin remote connections.
500-Watt VHF Low Band Transmitter Chapter 2, System Description325A, Rev. 0 2-10Table 2-11. VHF Amplifier Tray Remote Interface Connections with the A/V Inputand Remote Interface AssemblyFUNCTION REMOTE JACK/PINNUMBER INTERFACE TYPEForward Output Power (A6)VHF Amp J10-1Forward Output Power (A6)Rtn J10-21V full scale at 1kΩ sourceresistanceReflected O/P Power (A6)VHF Amp J10-3Reflected O/P Power (A6)Rtn J10-41V full scale at 1kΩ sourceresistanceForward Output Power (A7)VHF Amp J10-6Forward Output Power (A7)Rtn J10-71V full scale at 1kΩ sourceresistanceReflected O/P Power (A7)VHF Amp J10-8Reflected O/P Power (A7)Rtn J10-91V full scale at 1kΩ sourceresistance2.4 AC InputThe transmitter needs an AC input of 220VAC at 40 amps connected to it in orderto operate. The 220 VAC input connectsto (A2) the AC distribution panel in theupper middle rear of the cabinet. Thepanel contains the terminal block TB1that connects to the 220 VAC.The AC distribution panel contains fourcircuit breakers that supply the AC to therest of the transmitter. The input AC isconnected to the main AC circuit breakerCB1 (40 amps) that distributes the 220VAC to the terminal block TB2. TB2 hasthree MOVs, VR1, VR2, and VR3,mounted to the terminal block: one MOVis connected from each leg of the inputAC to ground and another is connectedacross the two legs. The input AC iswired from TB2 through three circuitbreakers, CB2, CB3, and CB4, to the restof the transmitter. CB2 is a 10-ampcircuit breaker that supplies the ACvoltage to the IEC outlet strip (A2-A1)that is connected into the VHF exciter,the (optional) receiver tray, and anyother optional accessories. CB3 is a 20-amp circuit breaker that supplies ACthrough J5 to the (A6) VHF amplifiertray. CB4 is a 20-amp circuit breaker thatsupplies AC through J6 to the (A7) VHFamplifier tray. When the VHF excitercircuit breaker is switched on, +12 VDCis supplied to that VHF amplifier tray forthe operation of the LED status indicatorsin the tray.

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