UBS Axcera 420A Low Power Television User Manual Chapter 2

UBS-Axcera Low Power Television Chapter 2

Chapter 2

100 Watt High Band VHF Transmitter Chapter 2, System Description420A, Rev. 0 2-1Chapter 2System DescriptionThe 420A is a complete 100 watt highband VHF solid-state internally diplexedtelevision transmitter that operates at anominal visual output power of 100 wattspeak sync and an average aural outputpower of 10 watts at a 10 dB A/Vratio,10% sound.The 420A has been submitted for typeacceptance to the FCC; the relevant FCCidentifier for the 420A is_________________.2.1 420A System OverviewThe 420A (1066428) consists of (A1) a100-watt, high-band VHFexciter/amplifier tray (1066308) and (A2)a bandpass filter assembly.The exciter/modulator section of the 100-watt, high-band VHF exciter/amplifiertray operates using either basebandaudio and video inputs. However, if the(optional) 4.5 MHz composite input kit(1273-1128) is purchased, the 4.5 MHzcomposite input or the baseband videoand audio inputs are used to produce adiplexed, modulated, on-channelfrequency visual + aural RF output. Theswitching between the 4.5 MHzgenerated by the baseband inputs or bythe 4.5 MHz composite input isaccomplished by a relay, on the sync tipclamp modulator board. The relay iscontrolled by a baseband select whichconnects to J18-6 and 7 on the rear ofthe tray. To operate the transmitter withthe (optional) 4.5 MHz composite inputkit using 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 to J18-6 and 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 J18-6 and7.The exciter/modulator section of the traytakes the baseband audio and videoinputs, or the (optional) 4.5 MHzcomposite input, and produces acombined 45.75 MHz + 41.25 MHz IFoutput that connects to J32 on the ALCboard. The combined IF output of theALC board connects to themixer/amplifier assembly where it isupconverted and filtered to the on-channel frequency visual + aural RFoutput. The RF is filtered and amplified inthe amplifier section to the 100-wattoutput power level. The RF output isfiltered in the bandpass filter assemblyand fed to the antenna via thetransmission line.The exciter and upconverter section ofthe tray operate when the circuit breakerCB1 is on, but the amplifier section onlyoperates when the transmitter is inOperate. This occurs because theswitching power supply that supplies theoperating voltages to the amplifiersection has an inhibit command appliedto it, shutting it off as long as thetransmitter is in Standby.2.1.1 Exciter SectionThe baseband video and audio inputs tothe transmitter connect to the rear panelof the tray. The baseband video or the(optional) 4.5 MHz composite inputconnects to jack (J2), which is a loop-through connected to jack (J1). Byremoving the termination jumper on thesync tip clamp/modulator board, jack(J1) can be used as a connection for thebaseband video or the 4.5 MHzcomposite input to another transmitter.The baseband audio input connects tothe terminal block (TB1) for balanced
100 Watt High Band VHF Transmitter Chapter 2, System Description420A, Rev. 0 2-2audio or to the BNC jack (J3) forcomposite audio, which is a loop-throughconnected to jack (J13). There are alsoconnections for the remote monitoringand operation of the transmitter at the"D"-connector jacks (J10 and J11).The baseband audio connects to (A4) theaural IF synthesizer board (1265-1303),in the exciter section, which provides theamplification for each of the threepossible audio inputs and the amplifiercircuit that supplies the single audiooutput. The board has the 4.5 MHz VCOand the aural modulation circuitry thatproduces the modulated 4.5 MHz output.The board also contains a PLL circuit tomaintain the precise 4.5 MHz separationbetween the aural (41.25 MHz) andvisual (45.75 MHz) IF frequencies. Thevideo input or 4.5 MHz composite inputto the exciter section connects to (A5)the sync tip clamp/modulator board(1265-1302) that takes the video inputand produces a sync tip clamped andmodulated visual IF + aural IF output atthe output jack J20. If the optional 4.5MHz composite input is purchased, theinput is directed out of the sync tipcamp/modulator board to the (A24)composite 4.5 MHz filter board (1227-1244) and the (A25) 4.5 MHz bandpassfilter board (1265-1307). These twoboards process the 4.5 MHz compositeinput and produce the video thatconnects back to the sync tipclamp/modulator board at J27. Theclamp portion of the board maintains aconstant peak of sync level of the videosignal over varying average picture levels(APL). The modulator portion of theboard contains the circuitry thatgenerates an amplitude-modulated,vestigial-sideband IF signal output at45.75 MHz.The 45.75 MHz is generated by (A7) theIF oven oscillator board (1191-1404) andconnected (+5 dBm) to the sync tipclamp/modulator board. The combinedvisual IF + aural IF output (0 dBm)connects to J32 on (A8) the ALC boardand then through relays to the rest of theALC board. The ALC board gives theoperator control over the output powerlevel of the transmitter by adjusting thelevel of the combined IF signal. The IFconnects out of the board at J3 and isdirected to (A9) an IF phase correctorboard (1227-1250). The IF signal isphase corrected as needed and fed backto the ALC board.2.1.2 Upconverter SectionThe output of the ALC board (0 dBm)connects to (A11-A1) the filter/mixerboard (1150-1102), in the (A11)mixer/amplifier enclosure (1065007),which takes the LO and heterodynes itwith the combined IF. This signal is thenfed to the high-band VHF filter/amplifierboard, high output (1064150), thatamplifies the RF signal and feeds it to the(A23) high-band amplifier heatsinkassembly (1065008). The crystalfrequency needed to generate the LO isproduced by (A14-A1) the channeloscillator board (1145-1201) in (A14) thechannel oscillator assembly (1145-1202).The crystal frequency (+5 dBm) from theoscillator is multiplied four times by(A15-A1) the x4 multiplier board (1174-1112), in (A15) the multiplier enclosure(1235-1101), which produces the LOsignal.2.1.3 Amplifier SectionThe RF output of the upconverter section(+11 dBm) is fed to the amplifier sectionof the transmitter. The amplifier sectionconsists of an (A23) amplifier heatsinkassembly (1065008) and associatedcomponents. The first stage of theamplifier section amplifies the RF to +31dBm in (A23-A1) a high-band VHFamplifier board assembly (1065812) thatconsists of a high-band VHF amplifierboard (1218-1201) and associatedcomponents. The RF is divided by the(A23-A2) 2-way combiner assembly(1064485) and fed to two parallel (A23-A3 and A23-A4) high-band VHF amplifierboard assemblies (1065812). Theamplified signals are fed to another (A23-
100 Watt High Band VHF Transmitter Chapter 2, System Description420A, Rev. 0 2-3A5) 2-way combiner board. The RFoutput from the 2-way combiner board(+51 dBm) is fed through (A31) anoutput coupler board (1088-1104) thatprovides a forward power sample to(A19) the visual/aural metering board(1265-1309). A forward sample connectsto the transmitter control board thatsupplies the voltage sample to the frontpanel meter of the tray. The reject portof the output coupler board provides thereject sample to the visual/auralmetering board. The metering boardconnects the reflected sample to thetransmitter control board for VSWRcutback and front panel-reflectedmetering for the tray.2.1.4 Bandpass Filter AssemblyThe output from the (A1) 100-watt, high-band VHF exciter/amplifier tray is fed tothe input of the (A2) bandpass filterassembly. The signal is fed to the (A2-A1) 5-section bandpass filter with trapsand then through (A2-A2) a high-bandVHF coupler assembly that provides afiltered RF sample for test purposes.2.1.5 Operational VoltagesThe transmitter needs an AC input of 115or 230 VAC at 10 amps connected to it,through the AC power plug, in order tooperate. The tray is set at the factory tooperate at the proper input voltage. Thisis accomplished by setting the (A1)power entry module to the correct linevoltage.2.1.6 Configuration of the PowerEntry Module AC InputFor 115 volts, verify that 115V isindicated on the rear panel cover on thepower entry module. If it is not, gentlyopen the cover, remove the fuseassembly, and reinsert it so that 115V isvisible with the cover closed.For 230 volts, verify that 230V isindicated on the rear panel cover on thepower entry module. If it is not, gentlyopen the cover, remove the fuseassembly, and reinsert it so that 230V isvisible with the cover closed.The input AC voltage connects from thejack (J14), which is part of (A1) thepower entry module on the rear of thetray, to (CB1) a 10-amp circuit breakerthat is also on the rear of the tray. Theswitched AC is wired through (A1) thepower entry module. This modulecontains two fuses, one on each line, tothe terminal block (TB2). TB2 has fourMOVs mounted to the terminal block, oneconnected from each leg of the input ACto ground and one across each of the twolegs, for surge and transient voltageprotection of the tray.The input AC is wired from TB2 to (A28)the switching power supply and to (A2) atoroid transformer. The (A28) switchingpower supply (1063547) provides the+48 VDC to operate the amplifierassembles and also to (A10) the +48VDC fan in the tray. The step-downtoroid (A2) supplies two 16 VAC outputs,through the terminal block (TB2), to (A3)the +12V(4A)/-12V(1A) power supplyboard (1265-1312). The AC connects onthe board to two full-wave bridgenetworks for +12 VDC and one full-wavebridge network for -12 VDC. The rectifiedDC from the +12 VDC full-wave bridgenetworks is connected to the (U1-U4)current limiting voltage regulator ICs.The rectified DC from the -12 VDC full-wave bridge network is connected to the(U5) current limiting voltage regulatorICs. The ±12 VDC outputs connect to therest of the boards in the tray throughjacks (J3-J8).
100 Watt High Band VHF Transmitter Chapter 2, System Description420A, Rev. 0 2-42.1.7 Control and StatusMeters, switches, and LED indicators aremounted on (A17) the transmitter controlboard (1068933). The control board isattached to the back of the front panel toallow for the switches and the LEDs to beoperated or viewed from the front of thetray. The (S1) Operate/Standby switchcontrols the output of the transmitter byapplying or removing the inhibitcommand to the switching power supplythat provides the DC supply voltages tothe amplifier section.In Operate, the green LED (DS2) is onand the inhibit command is removed.When in Standby, the amber LED (DS1)is on and the inhibit command is applied.Switch (S2) is an Automatic/Manualswitch that controls the operation of thetransmitter by the presence of the videoinput signal. When the switch is inAutomatic, the green LED (DS3) is litand, if the video input signal is lost, thetransmitter automatically switches toStandby after a short delay. When thevideo input signal returns, thetransmitter immediately switches back toOperate. In Manual, the amber LED(DS4) 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 the tray also has LEDsthat indicate Video Fault (Loss) (red LED[DS9]) and VSWR Cutback (amber LED[DS7]). The meters, switches, and LEDsfound in the 420A are described in thefollowing tables.
100 Watt High Band VHF Transmitter Chapter 2, System Description420A, Rev. 0 2-5Table 2-1. MetersMETER FUNCTIONMETER (A18)(mounted on the front panel) Displays power in terms of a percentage ofthe calibrated output power level. A full-scale reading is 120%. A reading of 100%is equivalent to the full-rated peak of syncvisual output power, 100 watts. Also reads% Exciter, % Reflected, and % Aural Poweralong with the ALC voltage, video, andaudio levels.SWITCH (S3), METER(mounted on the front panel) Selects the desired % Power, ALC voltage,video, or audio level readingALC(0-1 V) Displays the ALC voltage level (.85 VDC)% EXCITER(0-120) Displays the % Exciter Output power (levelneeded to attain 100% output power)% REFLECTED(0-120) Displays the % Reflected Output power(<10%)% VISUAL POWER(0-120) Displays the % Visual Output power of thetransmitter (100%=100 watts peak ofsync)% AURAL POWER(0-120) Displays the % Aural Output power of thetransmitter (100%=10 watts at 10 dBA/V ratio)VIDEO(0-1V) Displays the video level (1V at white with.3V sync only, -40 IRE)AUDIO(0-100kHz) Displays the audio level (±25 kHz balancedor ±75 kHz composite); will not read if onlythe 4.5 MHz composite input kit is used
100 Watt High Band VHF Transmitter Chapter 2, System Description420A, Rev. 0 2-6Table 2-2. Switches (mounted on the front panel)SWITCH FUNCTIONTRANSMITTER (S1) The momentary contact switch (S1) appliesa ground to K1, latching relay, located onthe transmitter control board.OPERATE/STANDBY K1 will switch either to Operate or toStandby depending on which direction S1 ispushed. When switched to Operate, theinhibit command is removed from theswitching power supply. This allows theswitching power supply to apply 48V to theamplifier boards. When switched tostandby, the power supply is disabled.MODE SELECT (S2) The momentary contact switch (S2) appliesa ground to latching relay K2, on thetransmitter control board.AUTO/MANUAL K2 will switch the transmitter to theAutomatic or Manual mode depending onwhich direction S2 is pushed. In Automatic,the video fault command from the ALCboard will control the operation of thetransmitter. The transmitter will switch toStandby after a slight delay, if the inputvideo is lost, and will switch back toOperate when the video is restored. InManual, the transmitter is controlled by theoperator using the front panelOperate/Standby switch or by remotecontrol.Table 2-3. AdjustmentsADJUSTMENT DESCRIPTIONGAIN (A20-R1) Adjusts the gain of the RF output using theALC board when the IF ALC circuit isEnabled
100 Watt High Band VHF Transmitter Chapter 2, System Description420A, Rev. 0 2-7Table 2-4. Control Indicators (LEDs mounted on the front panel)INDICATOR FUNCTIONOPERATE (DS2 GREEN) Indicates that the transmitter is inOperateSTANDBY (DS1 AMBER) Indicates that the transmitter is inStandbyAUTO (DS3 GREEN) Indicates that the transmitter is inAutomatic mode; switches to Standby if theinput video signal is lostMANUAL (DS4 AMBER) Indicates that the transmitter is in Manualmode; will not automatically switch toStandby if the input video signal is lostTable 2-5. Status Indicators (LEDs mounted on the front panel)INDICATOR FUNCTIONVIDEO LOSS (DS9 RED) Indicates that the input video has been lostto the transmitter. The fault is generatedon the ALC board.VSWR CUTBACK (DS7 AMBER) Indicates that the reflected power level ofthe transmitter has increased above 20%;this will automatically cut back the outputpower level to 20%. The fault is generatedon the transmitter control board.Table 2-6. Samples (BNC connectors mounted on the front panel)SAMPLE DESCRIPTIONf(s) A sample of the channel oscillator outputtaken from the sample jack of the channeloscillator assembly. The (fC) channelRF frequency equals four timesthe crystal frequency (fS) minus the (fIF) IFfrequency.f(IF) A sample of the 45.75 MHz output from theIF carrier oven oscillator boardf(IC) A sample of the 4.5 MHz intercarrieroutput from the aural IF synthesizer boardEXCITER O/P An output power sample of the excitertaken from the VHF filter/amplifier board,high output2.1.8 Input and Remote ConnectionsThe baseband video and audio inputsalone or, if the (optional) 4.5 MHzcomposite input kit (1273-1326) ispurchased, the 4.5 MHz composite inputor the baseband video input and audioinput to the transmitter, connect to therear of the tray. The baseband videoinput, or the 4.5 MHz composite input,connects to jacks J1 or J2, which areloop-through connected. The basebandaudio input connects to TB1 for balancedaudio or to jacks J3 or J13, which are
100 Watt High Band VHF Transmitter Chapter 2, System Description420A, Rev. 0 2-8loop-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 4.5MHz composite input connected to J1 orJ2. The baseband select command mustalso be removed from J18-6 and 7.Remote monitoring and operation of thetransmitter is provided through the jacks(J10 and J11) on the rear of the tray.Jack (J11) should have a dummy plugconnected to it, with a jumper connectedbetween pins 23 and 24, that providesthe interlock needed to operate thetransmitter. If this jumper is missing, thetransmitter will not switch to Operate. Ifremote connections are made to thetransmitter, they should be madethrough the plug in J11 or to J10 in thepositions noted in Table 2-7.Note: If the optional 4.5 MHzcomposite input kit is purchased, thebaseband select connects to J18,pins 6 and 7, on the back of the tray.The remote interface connections for the420A transmitter are listed in Table 2-7.These connections are made to jack(J11), the 37-position, "D"-connector, orto jack (J10), the 25-position, "D"-connector, on the rear panel of the tray.Note: Only the pins called out inTable 2-7 are utilized in thistransmitter.Table 2-7. Remote Interface ConnectionsFUNCTION REMOTE JACK/PINNUMBER INTERFACE TYPETransmitter Enable Interlock J11-24Transmitter Enable InterlockRtn J11-23J11-24 and 23 must bejumpered together fornormal operation; (1176-1038) jumper jackshould be used.Remote Control CommandsTransmitter Standby(Disable) J11-22 Contact closureTransmitterStandby/Operate Rtn J11-21Transmitter Operate(Enable) J11-20 Contact closureTransmitter Manual J11-9 Contact closureTransmitter Auto/ManualRtn J11-36Transmitter Auto J11-8 Contact closurePower Level Raise (optional) J10-11 Contact closurePwr Lvl Raise/Lower Rtn(optional) J10-13Power Level Lower(optional) J10-12 Contact closure
100 Watt High Band VHF Transmitter Chapter 2, System Description420A, Rev. 0 2-9Table 2-7. Remote Interface ConnectionsFUNCTION REMOTE JACK/PINNUMBER INTERFACE TYPEModulator Select (optional) J11-10 Contact closureModulator Select Rtn(optional) J11-30Remote Status IndicationsTransmitter Operate(Enable) Ind J10-3 50 mA max. current sinkOperate/Standby Ind Return J10-16Transmitter Standby(Disable) Ind J10-4 50 mA max. current sinkTransmitter Auto Indicator J11-7 50 mA max. current sinkAuto/Manual IndicatorReturn J11-32Transmitter ManualIndicator J11-6 50 mA max. current sinkVSWR Cutback Indicator J11-37 50 mA max. current sinkVSWR Cutback IndicatorReturn J11-35Video Loss (Fault) Indicator J11-25 50 mA max. current sinkVideo Loss (Fault) Ind. Rtn J11-31Receiver Fault (optional) J11-12Remote MeteringVisual Output Power J11-26Visual Output Power Rtn J11-28 1V full scale At 1kΩsource resistanceAural Output Power J11-27Aural Output Power Rtn J11-29 1V full scale At 1kΩsource resistanceReflected Power J10-5Power Rtn J10-22 1V full scale At 1kΩsource resistanceExciter Output Power J10-10Power Rtn J10-22 1V full scale At 1kΩsource resistance

Navigation menu