UBS Axcera 840A 10,000-watt UHF solid state television transmitter User Manual Chapter 5

UBS-Axcera 10,000-watt UHF solid state television transmitter Chapter 5

Chapter 5

10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-1 Chapter 5Detailed Alignment ProceduresThis transmitter was aligned at thefactory and should not require additionalalignments to achieve normal operation.Before beginning the alignmentprocedures, check that the RF output atJ2 of (A18) the output coupler assemblyof the transmitter is terminated into adummy load or is connected to theantenna. While performing anyalignments, refer to the Test Data Sheetfor the transmitter and compare the finalreadings from the factory with thereadings on each of the trays. Theyshould be very similar. If a reading is offby a substantial amount, the problem islikely to be in that tray.5.1 (A1-A4) UHF Exciter Tray(1063301; Appendix A)If the (optional) 4.5-MHz composite inputkit has been purchased, the UHF excitertray is capable of operating using eitherthe 4.5-MHz composite input or thebaseband audio and video inputs. The kitadds (A24) the composite 4.5-MHz filterboard and (A25) the 4.5-MHz bandpassfilter board to the UHF exciter. The 4.5MHz generated by the aural IFsynthesizer board is not used when the4.5-MHz composite input kit has selectedthe 4.5-MHz intercarrier signal generatedby the 4.5-MHz composite input. Thecomposite 4.5-MHz filter board and the4.5-MHz bandpass filter board are notused when the 4.5-MHz composite inputkit uses the 4.5-MHz intercarrier signalgenerated by the baseband video andaudio inputs with baseband select.The exciter tray has been factory tunedand should not need to be aligned toachieve normal operation. To align theUHF exciter for 4.5-MHz composite input,apply the 4.5-MHz composite input, withthe test signals used as needed, to videoinput jack J1 on the rear of the tray.Select the 4.5-MHz composite input byremoving the baseband select from J7-6and J7-7 on the rear of the tray, ifapplied.To align the UHF exciter using basebandvideo and audio inputs, connect thebaseband video, with the test signalsused as needed, to video input jack J2 onthe remote interface panel. For balancedaudio input, connect the baseband audioto TB1-1(+), TB1-2(-), and TB1-3 (GND)on the remote interface panel. Forcomposite/stereo audio, connect thestereo source to J6 on the remoteinterface panel.5.1.1 (A6) (Optional) Delay EqualizerBoard (1227-1204; Appendix B)This board has been factory tuned andshould not be retuned without the properequipment. If it is necessary to tune theboard:1. Select a sinX/X test signal as thevideo source to the delay equalizerboard.2. Monitor the video output of theboard at video sample jack J2 witha video measuring set (VM700) thathas been adjusted to measuregroup delay.3. Tune the four stages of the boardusing the variable inductors (L1-L4)and potentiometers (R7, R12, R17,and R22) until the signal attains theFCC group delay curve. The stagesare arranged in order of increasingfrequency. Adjust R29 as needed toattain the same level coming out ofthe board as is going into theboard.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-2 5.1.2 (A24) (Optional) Composite4.5-MHz Filter Board (1227-1244;Appendix B)The (A24) (optional) composite 4.5-MHzfilter board will only function properlywith a 4.5-MHz composite input signaland with the 4.5-MHz composite inputselected.Connect the test signal from an envelopedelay measurement set to the videoinput of the tray at J1 or J2.Connect an oscilloscope to jack J7, videoout, between the J7 center pin and pin 1or 3 ground. Adjust C21, frequencyresponse, if needed, for the bestfrequency response. Adjust R32, videogain, for a signal level of 1 Vpk-pk on theoscilloscope.The output at J6 and J7 of the boardshould be video only with no 4.5-MHzaural subcarrier.5.1.3 (A25) (Optional) 4.5-MHzBandpass Filter Board (1265-1307;Appendix B)The (A25) (optional) 4.5-MHz bandpassfilter board will only function properlywith a 4.5-MHz composite input signaland with the 4.5-MHz composite inputselected.Adjust the filter with L2, C3, L4, and C7for a frequency response of no greaterthan ±.3 dB from 4.4 to 4.6 MHz.Adjust C19 for an overall peak-to-peakvariation of less than ±.3 dB from 4.4MHz to 4.6 MHz.Recheck the frequency response; it mayhave changed with the adjustment of theenvelope delay. If necessary, retune theboard.5.1.4 (A7) IF Carrier Oscillator Board(1191-1404; Appendix B)To align (A7) the IF carrier oscillatorboard:1. While monitoring J3 with aspectrum analyzer, observe the45.75-MHz visual IF (typical +5dBm).2. Connect a frequency counter to J3and adjust C17 for 45.750000 MHz.3. Connect a frequency counter to J1and check for 50 kHz; this is theaural phase lock loop (PLL)reference.5.1.5 (A5) Sync Tip Clamp/Modulator Board (1265-1302;Appendix B)To align (A5) the sync tip clamp/modulator board:1. Determine if jumper W4 on jack J3is present. Jumper W4 terminatesthe video input into 75Ω. Removejumper W4 if the video loop-through is required on the rearchassis at jacks J1 and J2.2. Set the controls R20, the white clip,R24, the sync clip, and R45, thesync stretch cut-in, to their fullycounter-clockwise (CCW) position.Set R48, the sync magnitude, fullyclockwise (CW).3. Place the jumper W7 on jack J4 tothe clamp off, disable, position.4. Connect a 5-step staircase videotest signal to the input of thetransmitter.5. Monitor TP2 with an oscilloscope.Adjust R12, the video gain pot, for1 Vpk-pk.6. Change the video input test signalto a multiburst test pattern. While
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-3 monitoring TP2, adjust C8 and R32for a flat-frequency response.Change the input video test signalback to the 5-step staircase.7. Monitor TP2 with an oscilloscope.Adjust the pot R41, manual offset,for a blanking level of -0.8 VDC.The waveform in Figure 5-1 shouldbe observed at this point. Movejumper W2 on J4 to the clampenable position. Adjust pot R152,depth of modulation, for a blankinglevel of -0.8 VDC.0 Volts.1 VoltsFigure 5-1. Waveform at TP2.Note: The waveform in Figure 5-1represents the theoretical level forproper modulation depth. Step 9below describes how to set themodulation depth through the use ofa television demodulator or a zero-spanned spectrum analyzer tuned tothe visual IF frequency.8. The following test setup is for theadjustment of the depth ofmodulation and ICPM at IF:A. Remove the cable that is nowon J18. Connect the doublesideband 45.75-MHz visual IFsignal from J18 to a 10-dBsplitter/coupler. Connect thecoupled port of the splitter/coupler to the RF input of atelevision demodulator.Connect the direct port to aspectrum analyzer.B. Connect the 75-Ω video outputof the demodulator to the videoinput of a waveform monitor.For incidental carrier phasemodulation (ICPM)measurements, also connectthe quadrature output of thedemodulator to the horizontalinput of the waveform monitorusing a 250-kHz low-pass filter.(An oscilloscope can be used inplace of a waveform monitor).C. Set the controls of thedemodulator as follows:• Detector Mode: Cont• Sound Trap: In• Zero Carrier: On• Auto: Sync• Audio Source: Split• De-Emphasis: In9. Move jumper W7 on J4 to the clampdisable position. Readjust pot R41,manual offset, for the correct depthof modulation by observing thedemodulated waveform on thewaveform monitor or on thespectrum analyzer set to zero span.10. Check the demodulated video forthe proper sync-to-video ratio (syncis 28.6% of the total white video
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-4 signal). If sync stretch is needed,adjust R45, sync stretch cut-in,until sync stretch occurs. AdjustR48, sync stretch magnitude, forthe proper amount of stretch.Readjust R41, manual offset, ifnecessary, for the correct depth ofmodulation.11. Move jumper W7 on J4 to the clampenable position. Readjust pot R152,the depth of modulation, for thecorrect depth of modulation.12. Set the waveform monitor todisplay ICPM. Preset R53 fully CCW,adjust C78 for the greatest effect atwhite on the ICPM display, andadjust R53 for minimum ICPM.13. Recheck the depth of modulationand, if necessary, adjust R152,depth of modulation.14. Adjust pot R70 for a level ofapproximately -10 dBm on thespectrum analyzer at J18.15. Remove the video input. Place thefront panel meter in the videoposition and, while monitoring themeter, adjust pot R144, zeroadjust, for a reading of zero.16. Replace the video input testsignal (the 5-step staircase).Turn the front panel meter tothe Video position and adjustR20 on the transmitter controlboard for a reading of 100 (10on the 0-to-10 scale). Thisboard does not have syncmetering.17. Reconnect the plug to J18 andmove the spectrum analyzer testcable to 41.25 IF output jack J16.Tune C59 and L17-L20 to maximizethe 41.25-MHz aural IF signal andminimize the out-of-band products.Adjust pot R97 for -20 dBm at J16.18. Reconnect the plug to J16 andmove the spectrum analyzer testcable to IF output jack J20. PresetR62, the visual IF gain pot, to themiddle. Insert a multiburst testsignal into the transmitter andobserve the visual frequencyresponse with the spectrumanalyzer set at 1 dB/division. TuneR63 and C30, the IF frequencyresponse adjustments, for a flat-frequency response (±0.5 dB).19. While still monitoring J20 with aspectrum analyzer, readjust R62,visual IF gain, for a visual outputlevel of 0 dBm. Adjust R85, A/Vratio, for a -10 dB aural-to-visualratio or to the needed A/V ratio.Reconnect the plug to J20.20. Using an input video test signal (the5-step staircase) with a 100 IREwhite level, monitor TP2 with anoscilloscope. Set the control R24,the sync clip, just below the pointwhere sync clipping begins to occur.Also, set R20, the white clip, to thepoint just below where the whitevideo begins to clip. Note: This procedure should beperformed after the system setup orif linearity problems occur.5.1.6 (A26) Diacrode VSBF BypassBoard (1293-1230; Appendix B)The (A26) diacrode VSBF bypass board isused to bypass the clamp board saw filterwhen S1 and S2 are in the enableposition. This double sideband signal canbe used to sweep the tube cavity with adouble sideband and no aural present. C2is used to flatten the double sidebandresponse. S1 and S2 are normally in thebypass position.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-5 5.1.7 (A4) Aural IF SynthesizerBoard, 4.5 MHz (1265-1303,Appendix B)1. The test equipment setup for (A4)the aural IF synthesizer board, 4.5MHz, is as follows:A. Connect a 600-Ω balancedaudio output from an audiooscillator to the balanced audioinput terminals of the tray atTB1-1 (+), TB1-2 (-), and TB1-3 (ground) on the rear chassis.B. Connect the combined IFoutput at J21, the IF sample onthe clamp modulator board, tothe input of an IF splitter.Connect one output of thesplitter to the videodemodulator and the otheroutput to the spectrumanalyzer.C. Connect a short cable at thefront of the demodulator fromthe RF-out jack to the IF-injack.D. Connect a cable from the 600-Ω audio output jack of thedemodulator to the input of anaudio distortion analyzer.2. Set the output frequency of theaudio oscillator to 400 Hz and theoutput level to +10 dBm.3. Center the aural carrier on thespectrum analyzer with thespectrum analyzer set to thefollowing:• Frequency/Division: 10 kHz• Resolution Bandwidth: 3 kHz• Time/Division: 50 msec• Trigger: Free runA. Adjust L5 for approximately+3.5 VDC at TP2.B. The green LED DS1 should beilluminated, indicating a lockedcondition. If not, retune L5 fora locked condition.4. Adjust R13, balanced audio gain, onthe aural IF synthesizer board for±25 kHz deviation.5. Check the distortion on the auraldistortion analyzer (< 0.5%).6. Disconnect the 600-Ω balancedaudio input to the tray. Connect a75-Ω stereo audio input (400 Hz at1 Vpk-pk) to composite audio inputjack J3 on the rear of the tray.Follow the procedure in the stereogenerator instruction manual formatching the level of the generatorto the exciter. R17 is used to adjustthe composite audio gain.7. Check the distortion level on thedistortion analyzer (< 0.5%).5.1.8 (A8) ALC Board (1265-1305;Appendix B) (Part 1 of 2)The following details the meaning of eachLED of (A8) the ALC board when it isilluminated:• DS1 - Red LED: Indicates that anabnormally low IF signal level ispresent at IF input connector J1• DS2 - Red LED: Indicates that theALC circuit is unable to maintain thesignal level requested by the ALCreference; this is usually due toexcessive attenuation in the linearityor the IF phase corrector signal path,or because the jumper W3 on J6 is inmanual gain• DS3 - Red LED: Indicates a video lossfault• DS4 - Red LED: Indicates that a Mutecommand is present (not used in thisconfiguration)
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-6 • DS5 - Green LED: Indicates that theoutput from the modulator is selectedas the input to the ALC board1. To align the ALC board, preset thefollowing controls in the UHF excitertray:• ALC board – Move jumper W1 on J4to disable, between pins 2 and 3 (todisable linearity correctors); movejumper W3 on J6 to manual, betweenpins 2 and 3 (for manual gaincontrol); adjust R87, the manual gainpot, to mid-range• IF phase corrector board – Movejumper W2 on J9 to the phasecorrection enable position; move thejumper W3 on J10 to the amplitudecorrection disable position.2. The combined IF output of the synctip clamp modulator board is cabledto jack J32 of the ALC board.Remove J32 from the board andcheck to see that DS1, Input Fault,is illuminated. Reconnect J32 andcheck to see that DS1 isextinguished.3. Jumper W3 on J6 should be in themanual position; monitor jack J3with a spectrum analyzer.4. With a multiburst video signalpresent, tune C4 for a flat-frequency response of ±0.5 dB.5. Before proceeding with part 2 of theALC board alignment (described insection 5.1.10), check the IF phasecorrector board to make sure that itis functioning properly.5.1.9 (A9) IF Phase Corrector Board(1227-1250; Appendix B)Refer to the system alignmentprocedures at the end of this chapter forthe set up of (A9) the IF phase correctorboard in the exciter tray. The signal levelinto the board should be approximatelythe same as the output of the board.The IF input jack of the IF phasecorrector board is fed from J3, the IFoutput jack of (A8) the ALC board.The IF output jack of the IF phasecorrector board is fed to J7, the IF inputjack of (A8) the ALC board.5.1.10 (A8) ALC Board, NTSC (1265-1305; Appendix B) (Part 2 of 2)Input a multiburst video test signal at thebaseband video input. Connect aspectrum analyzer to J11. Tune C63 for aflat-frequency response of ±0.5 dB.Move the Operate/Standby switch on thefront panel of the transmitter to theOperate position.Place jumper W3 on jack J6 in theManual mode and adjust R87 for 0.8volts at TP4.Place jumper W3 on J6 in the Auto modeand adjust the front panel power adjustcontrol A20 fully CW. If the optionalremote power raise/lower kit is present,adjust switch S1 on the board tomaximum voltage at TP4. Adjust R74,the range adjust, for 1 volt at TP4.Adjust the front panel power adjustcontrol (A20) for 0.8 VDC at TP4. If theoptional remote power raise/lower kit ispresent, adjust switch S1 on the board tothe mid-range of its travel and thenadjust the front panel Power Adjustcontrol (A20) for 0.8 VDC at TP4.Disconnect the plug that is now on J12(IF output) and monitor the output with aspectrum analyzer. The output should beapproximately 0 dBm. Adjust R99, ifnecessary, to increase the output level. Ifa smaller output level is needed, movethe jumpers J27 and J28 to pins 2 and 3and adjust R99 as needed. ReconnectJ12.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-7 Move W2 on J5 to the cutback enableposition. Remove the input video signaland verify that the output of thetransmitter drops to 25%. Adjust R71,the cutback level, if necessary. Restorethe video input signal.Note: This step affects the responseof the entire transmitter. Connect avideo sweep signal to the input ofthe tray. Monitor the output of thesystem with a spectrum analyzer.Adjust C71 with R103 and C72 withR106, as needed, to flatten theresponse. C71 and C72 can beadjusted for the frequency of thecorrection notch being applied to thevisual response of the transmitter.R103 and R106 are used to adjustthe depth and width of the correctionnotch.Controls R13, R18, and R23, themagnitude controls, should be set fullyCW. Controls R34, R37, and R40 are thelinearity cut-in adjustments.5.1.11 (A11) UHF Upconverter Board(1265-1310; Appendix B)To align (A11) the UHF upconverterboard, place W1 on J10 in the Manualposition. R10 is a gain control that isadjusted to give an output ofapproximately +17 dBm at J5 of theboard with an input of 0 dBm of IF.5.1.12 (A14-A1) Channel OscillatorBoard (1145-1201; Appendix B)The (A14-A1) channel oscillator board ismounted in (A14) the channel oscillatorassembly. To align this board:1. Connect J1, the main output of thechannel oscillator, to a spectrumanalyzer tuned to the crystalfrequency. Peak the tuningcapacitors C6 and C18 formaximum output. Tune L2 and L4for maximum output. The outputlevel should be about +5 dBm. Thechannel oscillator should maintainan oven temperature of 50° C.If a spectrum analyzer is notavailable, connect a digitalvoltmeter (DVM) to TP1 on the x8multiplier board. Tune capacitors C6and C18 for maximum voltage andtune L2 and L4 for maximumvoltage output at TP1.2. Connect J2, the sample output ofthe channel oscillator, to a suitablecounter and tune C11, coarseadjust, to the crystal frequency.Tune C9 for the fine-frequencyadjustment.Caution: Do not repeak C6, C18, L2,or L4. This can change the outputlevel.Note: While adjusting C9 and C11 tothe crystal frequency, the peakvoltage monitored at TP1 of the x8multiplier board should not decrease.If a decrease does occur, there maybe a problem with the crystal.Contact the ADC Field ServiceDepartment for further instructions.Note: If the channel oscillator in thechannel oscillator assembly is used,the C9 fine-frequency adjust is noton the channel oscillator board. Itcan be found on the FSKw/EEPROM board by using R9.3. Reconnect J1, the main output ofthe channel oscillator, to J1, theinput of the x8 multiplier.5.1.13 (A15-A1) x8 Multiplier Board(1227-1002; Appendix B)The (A15-A1) x8 multiplier board ismounted in an x8 multiplier enclosureassembly. During normal operation, thegreen LED DS1, which can be seenthrough the access hole in the enclosureassembly, will be lit to indicate that theLO is present at the output of the x8multiplier board.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-8 Connect a spectrum analyzer tooutput jack J2 of the board.Tune C4, C6, C10, C12, C18, and C20 formaximum output.Readjust all of the capacitors to minimizethe seventh and the ninth harmonics ofthe channel oscillator frequency. Theyshould be at least -30 dB down withoutaffecting the x8 multiplier output.If a spectrum analyzer is not available, aDC voltmeter can be used. When avoltmeter is used, the harmonicfrequencies must be minimized toprevent interference with other channels.While monitoring each test point with aDC voltmeter, maximize each test pointby tuning the broadband multipliers inthe following sequence:• Monitor TP1 with a DVM and tune C4for maximum (typical 0.6 VDC).• Monitor TP2 and tune C6 and C10 formaximum (typical 1.2 VDC).• Monitor TP3 and tune C12 and C18for maximum (typical 2.0 VDC).• Monitor TP4 and tune C20 formaximum.• Repeak C12 and C10 whilemonitoring TP4 (typical 3.5 VDC).• The typical output level is +15 dBm.5.1.14 (A19) Visual/Aural MeteringBoard (1265-1309; Appendix B)The (A19) visual/aural metering board isadjusted to give a peak-detected outputindication to the front panel meter for thevisual output and aural output of thedriver cabinet. The board should notneed to be adjusted to achieve normaloperation.5.1.15 (A3) +12 VDC (4A)/-12 VDC(1A) Power Supply Board (1265-1312; Appendix B)There are no adjustments that need tobe made to (A3) the +12 VDC (4A)/-12VDC (1A) power supply board. DS1 willbe lit if a +12 VDC output is connected toJ6. DS2 will be lit if a +12 VDC output isconnected to J3. DS3 will be lit if a +12VDC output is connected to J4. DS4 willbe lit if a +12 VDC output is connected toJ5. DS5 will be lit if a -12 VDC output isconnected to J7 and J8.5.1.16 Transmitter Control Board(1293-1221; Appendix B)To align the VSWR cutback, adjust the 3-watt amplifier tray for a 12.5% VisualPower reading on the metering controlpanel. Reverse the J6 and J3 cables on(A2-A2) the coupler on the output of thediacrode cavity. Adjust R22 unto theVSWR light starts to illuminate on theexciter front panel. Place the J3 and J6cables back in their original positions.To align the video metering, insert acomposite or some other 100-IRE testsignal into the exciter tray. Adjust R20for a full-scale reading (1 volt) on thebottom scale of the front panel meter ofthe exciter tray in the video meteringposition.To align the audio metering, adjust theaudio input level for a ±25 kHz deviationusing a spectrum analyzer. Adjust R19 onthe board for a 25-kHz reading on thebottom scale of the front panel meter ofthe exciter tray.This completes the detailed alignmentprocedures for the UHF exciter tray.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-9 5.2 (A9) 3-Watt Amplifier Tray(1068203; Appendix A)The 3-watt amplifier tray has beenaligned at the factory and should notrequire any further adjustments. If analignment is necessary, terminate the 3-watt tray into a dummy load beforeperforming any adjustments.5.2.1 (A1) UHF Filter (1007-1101;Appendix B)The (A1) UHF filter (1007-1101) hasbeen factory swept and should not betuned without the proper equipment. Thefiltered output is sent to (A2) the AGCboard input jack J1.5.2.2 (A2) AGC Board (1007-1201;Appendix B)Perform the following steps to align (A2)the AGC board (1007-1201):1. With S1 on the AGC board in theManual position, adjust R32 for abouta -2 dBm output at J2.2. The RF output of the AGC board is fedto (A27) the UHF phase shifter boardinput jack J1.5.2.3 (A27) UHF Phase Shifter Board(1142-1315; Appendix B)The (A27) UHF phase shifter board(1142-1315) adjusts the phase of thesignal to produce the maximum output ofthe transmitter when the two parallelamplifiers are added together.Adjust R7 on the front panel of the trayfor maximum output power. Monitor thecombined % Output power on the frontpanel meter of the transmitter.The phase-corrected RF output is fed to(A3) the UHF amplifier/regulator boardinput jack J1.5.2.4 (A3) UHF Amplifier/RegulatorBoard (1007-1204; Appendix B)The (A3) UHF amplifier/regulator board(1007-1204) has no tuning adjustmentsand has a gain of about +17 dB. Theoutput is fed to (A5) the 3-watt amplifierboard #1 input jack J1.5.2.5 (A5) 3-Watt Amplifier # 1(1007-1211; Appendix B)The (A5) 3-watt amplifier #1 (1007-1211) has a gain of about 9 dB and istuned with C2, C4, and C8 for maximumoutput.The operating current, static current withno drive applied, of the amplifier is set to800 milliamps with R7 on (A6) the opto-bias board. The current is determined bymeasuring the voltage drop across R3,the 3.3-ohm resistor in the collectorcircuit of Q1 on the amplifier board, andadjusting R7 for a voltage drop of 2.64volts.The RF output is fed to (A7) the 3-wattamplifier board #2.5.2.6 (A7) 3-Watt Amplifier # 2(1007-1211; Appendix B)The (A7) 3-watt amplifier #2 (1007-1211) has a gain of about 9 dB and istuned with C2, C4, and C8 for maximumoutput.The operating current of the amplifier isset to 850 mA with R7 on (A8) the opto-bias board. The current is determined bymeasuring the voltage drop across R3,the 3.3-ohm resistor in the collectorcircuit of Q1 on the amplifier board, andadjusting R7 for a voltage drop of 2.8volts.The output of the amplifier is fed through(A9) the UHF dual coupler assembly toRF output jack J2 of the tray. A forwardand reflected power sample is taken fromthe UHF dual coupler assembly and fed to(A10) the dual peak detector board.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-10 5.2.7 (A10) Dual Peak DetectorBoard (1002-1208; Appendix B)While monitoring the RF output of (A10)the dual peak detector board (1002-1208), adjust R32 on (A2) the AGC boardfor a reading of 3-watts peak envelopepower (3 watts CW). While in the Outputposition of the Meter Selector switch,adjust R14 on the dual peak detectorboard for a reading of 100% on the frontpanel meter.Move the cable from J1 of the dual peakdetector board to J2. Move the MeterSelector switch to the Reflected Powerposition and adjust R16 on the dual peakdetector board for a reading of 100%.Replace the cable onto J1.5.2.8 (A2) AGC Board (1007-1201;Appendix B)Remove RF input J1 to (A2) the AGCboard (1007-1201) and adjust R10 for areading of 0 volts on TP1. Replace the RFinput. The nominal reading at TP1 shouldbe +.35 volts.If necessary, adjust R32 for an outputpower reading of 100%. Switch S1 to theAGC position and adjust R49 for areading of 100% on the Output Powermeter.5.2.9 (A25) AGC Control Board(1137-1201; Appendix B)To align (A25) the AGC control board(1137-1201), measure TP3 with a DVMand adjust R3, gain #1, for a 0.9 voltnominal reading. Then, if the outer loopAGC is used, adjust R12, gain #2, for 1volt, with the output of the transmitter atthe normal output level.5.2.10 (A29) Overdrive ProtectionBoard (1142-1626; Appendix B)To set up the override circuit, check thatthe output power level of the transmitteris at 100% with a sync-only 0 IRE testsignal. Adjust R11 for a reading of .4VDC at TP1.Increase the output power level of thetransmitter to 110% and adjust R12 untilthe output power begins to drop off.Return the output power level of thetransmitter to 100%. The trip circuit mayneed to be readjusted if the amplifiertray is terminated into a different load.5.2.11 (A11) Power Supply ControlBoard (1007-1202; Appendix B)There are no adjustments to (A11) thepower supply control board (1007-1202).5.2.12 (A22) ±12V Power SupplyBoard (1062-1013; Appendix B)There are no adjustments to (A22) the±12V power supply board (1062-1013).5.2.13 (A16) +24V Power SupplyBoard (1007-1207; Appendix B)To adjust the power supply forovervoltage protection, start bypresetting R11 on (A16) the +24V powersupply board (1007-1207) fully CW.Measure the voltage at J1-10 with a DVMand adjust R8 for 25 volts. Adjust R11CCW until the power supply shuts off dueto overvoltage. Adjust R8 fully CCW. Turnoff the tray, wait a few seconds, and thenturn the tray back on. This will reset thepower supply board.While monitoring J1-10, slowly adjust R8CW toward 25 volts. If the power supplydoes not shut off at 25 volts, adjust R11slightly more CCW until it does shut off.Adjust R8 CCW. Reset the tray by turningthe tray off, waiting a few seconds, andthen turning the tray back on. Adjust R8CW while monitoring J1-10 and check tosee if the supply will now shut off at 25volts. If necessary, repeat this procedure.Adjust the output voltage of the board atJ1-10 to 24 volts using adjustableresistor R8.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-11 This completes the detailed alignmentprocedures for the 3-watt UHF amplifiertray.5.3 (A6, A7) 250-Watt Amplifier Tray(1044027/1044028/1044029;Appendix A)This tray has been adjusted at thefactory to meet all specifications,including feedforward correction, andshould not require any adjustments toattain normal operation.5.3.1 (A1-A1) Single Stage AmplifierAssembly, Class A (1286-1608/1286-1609/1286-1610; Appendix B)The (A1-A1) single stage amplifierassembly, class A, is made from ageneric single stage amplifier board,class A, with a frequency determining kit.This board operates class A and has again of approximately 11 dB. The bias ofthe transistor is set by the on-boardbiasing circuit. Adjust R6 for 5 amps ofidle current and no RF drive applied.Connect a voltage meter across E2 andE3 on (A15) the amplifier protectionboard and switch S1 to the #1 position.Adjust R6 for a reading of 50 mV.Connect a sweep test signal to J1, the RFinput jack of the UHF amplifier tray, andmonitor the output of the board at J2with a padded-input spectrum analyzer.Tune capacitor C5 for peak output andtune C6 for peak output power with aflat-frequency response at J2.5.3.2 (A1-A3) Stripline CouplerBoard (1286-1604; Appendix B)There are no adjustments to (A1-A3) thestripline coupler board.5.3.3 (A1-A5) Single Stage AmplifierAssembly, Class AB (1286-1605/1286-1606/1286-1607; Appendix B)The (A1-A5) single stage amplifierassembly, class AB, is made from ageneric single stage amplifier board,class AB, with a frequency determiningkit.This board operates class AB and has again of approximately 9 dB. The bias ofthe transistor is set by the on-boardbiasing circuit. Adjust R106 for 500milliamps and no RF drive applied.Connect a voltage meter across E2 andE3 on the amplifier protection board andswitch S1 to the #2 position. AdjustR106 for a reading of 5.0 mV. Connect asweep test signal to J1, the RF input jackof the UHF amplifier tray, and monitorthe output of the board at J2 with apadded-input spectrum analyzer. Tunecapacitor C105 for peak output and tuneC119 for peak output with a flat-frequency response and minimumcurrent at J2.5.3.4 (A19-A6) 2-Way SplitterAssemblyThere are no adjustments to (A19-A6)the 2-way splitter assembly (1044096).5.3.5 (A19-A7, A19-A8) Dual OutputPower Amplifier Assemblies, ClassAB (1286-1316/1286-1317/1286-1318; Appendix B)Each board in (A19-A7, A19-A8) the dualoutput power amplifier assemblies, classAB, is made from a generic dual stageamplifier board, class AB, with afrequency determining kit.These boards operate class AB and havea gain of approximately 9 dB. The idlingcurrent for each of the transistors is setto 250 mA.To adjust the idling currents, no RFapplied to the tray, of the devices on(A1-A7), connect a voltage meter acrossE2 and E3 on the amplifier protectionboard. Switch S1 to the #3 position andadjust R106 for a reading of 2.5 mV.Switch S1 to the #4 position and adjustR206 for a reading of 2.5 mV.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-12 To adjust the idling currents of thedevices, no RF applied to the tray, on(A1-A8), connect a voltage meter acrossE2 and E3 on the amplifier protectionboard. Switch S1 to the #5 position andadjust R106 for a reading of 2.5 mV.Switch S1 to the #6 position and adjustR206 for a reading of 2.5 mV.Connect a sweep test signal to J1, the RFinput jack of the UHF amplifier tray. On(A1-A7) the amplifier board, tunecapacitors C105 and C205 for peakoutput power. Tune C119 and C219 forpeak output power with a flat-frequencyresponse and minimum current.Connect a sweep test signal to J1, the RFinput jack of the UHF amplifier tray. On(A1-A8) the amplifier board, tunecapacitors C105 and C205 for peakoutput power. Tune C119 and C219 forpeak output power with a flat-frequencyresponse and minimum current.5.3.6 (A1-A9) 2-Way CombinerBoard (1292-1122/1292-1102/1292-1121; Appendix B)There are no adjustments to (A1-A9) the2-way combiner board.5.3.7 (A3) Phase/Gain AdjustModule (1286-1616; Appendix B)There is no basic setup for (A3) thephase/gain adjust module. All tuning oradjustments should be performed usingthe feedforward correction alignmentprocedure (see section 5.3.19).5.3.8 (A5) Stripline Coupler Board(1286-1604; Appendix B)There are no adjustments for (A5) thestripline coupler board.5.3.9 (A20-A1) Error AmplifierPhase/Gain Module (1286-1703;Appendix B)There is no basic setup for (A20-A1) theerror amplifier phase/gain module. Alltuning or adjustments should beperformed using the feedforwardcorrection alignment procedure (seesection 5.3.19).5.3.10 (A2-A2) 1-Watt UHF AmplifierAssembly (1286-1235; Appendix B)The (A2-A2) 1-watt UHF amplifier boardwithin the 1-watt amplifier assembly hasapproximately 10 dB of gain. There areno adjustments to this board.5.3.11 (A2-A3) Single StageAmplifier Assembly, Class A (1286-1608/1286-1609/1286-1610;Appendix B)The (A2-A3) single stage amplifierassembly, class A, is made from thegeneric single stage amplifier board,class A, with a frequency determining kit.This board operates class A and has again of approximately 11 dB. The bias ofthe transistor is set by the on-boardbiasing circuit. Adjust R6 for 5 amps ofidle current and no RF drive applied.Connect a voltage meter across E2 andE3 on (A15) the amplifier protectionboard and switch S1 to the #8 position.Adjust R6 for a reading of 50 mV.Connect a sweep test signal to J1, the RFinput jack of the UHF amplifier tray, andmonitor the output of the board at J2with a padded-input spectrum analyzer.Tune capacitor C5 for peak output andtune C6 for peak output power with aflat-frequency response at J2.5.3.12 (A7) 7-dB UHF Coupler (2011-1000/2011-1001; Appendix B)There are no adjustments to (A7) the 7-dB UHF coupler.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-13 5.3.13 (A8) UHF Coupler Assembly(1007-1208; Appendix B)There are no adjustments to (A8) theUHF coupler assembly.5.3.14 (A10) CirculatorThere are no adjustments to (A10) thecirculator.5.3.15 (A17) Dual Peak DetectorBoard (1002-1208; Appendix B)There are no adjustments to (A17) thedual peak detector board.5.3.16 (A15) Amplifier ProtectionBoard (1292-1125; Appendix B)There are no adjustments to (A15) theamplifier protection board.5.3.17 (A16) Amplifier Control Board(1292-1112; Appendix B)Note: The phase and gainadjustments should only beperformed during the feedforwardcorrection setup procedure (seesection 5.3.19).To set up the forward and reflectedmetering, perform the proceduredescribed in this section. The 250-watttray must be terminated into a dummyload rated for at least 250 watts and theamplifier Test switch should be enabledon the amplifier assembly meteringcontrol panel.Note: This procedure should only beperformed after the feedforwardcancellation setup in section 5.3.19,if required, has been completed.To set the video signal to 0 IRE with noaural, the aural must first be removedby pulling connector J16 from (A5) thesync tip clamp board in the exciter tray.Adjust manual gain pot R32 on (A2) theAGC board in the 3-watt amplifier trayfor 150 watts average power with 40IRE units of sync. Use correction or syncstretch, if necessary, to correct for 40IRE units of sync.Use a spectrum analyzer to referencethe visual carrier level.Reconnect the aural carrier at J16 on thesync tip clamp board with the correctV/A ratio from the exciter tray.Readjust R32, the manual gain pot, tomatch the visual carrier to the previousreference level. Use the correction orsync stretch again, if necessary, tocorrect for 40 IRE units of sync.Adjust R3 on (A16) the amplifier controlboard on the 250-watt amplifier tray fora 100% forward power meter reading onthe tray.Decrease the R32 manual gain pot onthe 3-watt tray for a 20% ForwardPower reading on the 250-watt amplifiertray meter.Disconnect the RF output from the 250-watt amplifier tray.Adjust R10 on (A16) the amplifiercontrol board on the 250-watt amplifiertray for a 20% reflected power meterreading.Reconnect the RF output to the 250-wattamplifier tray.Reset manual gain pot R32 on the 3-watt tray for a 100% forward powermeter reading.5.3.18 (A11) ASTEC America+26.5V/1500W Switching PowerSupply (VS1-L6-01-CE; Appendix B)The (A11) ASTEC America +26.5V/1500W switching power supply (VS1-L6-01-CE) contains no customer-repairableitems. If the power supply shouldmalfunction, do not attempt to repair thepower supply without first consulting theADC Field Service Department. The
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-14 power supply is adjusted to provide anoutput of +27 VDC.5.3.19 Calibration of theFeedforward Correction CircuitsNote: This procedure is factory setand should not need to bereadjusted in the field.Set up a network analyzer for thefollowing settings:• Frequency: Center of channel to betuned• Span: 20 MHz• Power level: > +10 dBm• Markers: > Center frequency, CF +6MHz, CF - 6 MHzTurn on the 250-watt amplifier tray andtune the main amplifier output powerpath for maximum gain. Verify that themain signal path is peaked.Verify that the response is within+/- 0.25 dB across the center frequency+/- 6 MHz. Using this main path as areference, calibrate Channel 1 of thenetwork analyzer for transmission.Turn off the 250-watt amplifier tray.Terminate (A18) the delay line outputwith a high-power termination andterminate the RF input on (A7) the 7-dBUHF coupler assembly.Terminate (A4) the delay line output andJ1 on (A5) the UHF dual stripline couplerboard.Turn on the 250-watt amplifier tray.Tune the correction amplifier path formaximum gain.Verify that the response is within+/- 0.25 dB across the center frequency+/- 6 MHz.Adjust R20, gain adjustment, on (A16)the amplifier control board until the gainis within 0.5 dB from the calibratedreference.Adjust R29, phase adjustment, on (A16)the amplifier control board until thephase is 180° from the calibratedreference.Make sure that the delay is within 5 nsecof the calibrated reference. Adjust A18)the delay line accordingly to achieve adelay of within 5 nsec.Note: The main output power pathwill need to be recalibrated if it isnecessary to adjust the delay line.After setting up the gain and phase, turnoff the 250-watt amplifier tray.Reconnect (A18) the delay line to (A7)the 7-dB UHF coupler assembly.Turn on the 250-watt amplifier tray andreadjust the R20 gain adjustment andthe R29 phase adjustment for the bestcancellation across the center frequency+/- 6 MHz.Note: The cancellation should be>20 dB.Turn off the 250-watt amplifier tray.Disconnect (A18) the delay line and re-terminate it with a high-powertermination.Re-terminate the RF input on (A7) the7-dB UHF coupler assembly with a 1-watt termination.Turn on the 250-watt amplifier tray and,using this path as the reference,calibrate Channel 1 of the networkanalyzer for transmission.Turn off the 250-watt amplifier tray.Disconnect and terminate J4 from (A5)the UHF stripline coupler board.Terminate the rigid line going to J4 of(A5) the UHF stripline coupler board.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-15 Reconnect (A4) the delay line to J1 of(A5) the UHF stripline coupler board.Turn on the 250-watt amplifier tray andadjust capacitors C1 and C2 on (A3) thephase/gain adjust module until they are180° from the 2nd calibrated reference.Adjust R22, gain adjust, on (A16) theamplifier control board until the gain iswithin 0.5 dB.Make sure that the delay is within 5 nsecfrom the 2nd calibrated reference. Adjust(A4) the delay line accordingly toachieve this delay.After setting up the gain and phase, turnoff the 250-watt amplifier tray.Reconnect the rigid line to J3 of (A5) thedual UHF stripline coupler board.Turn on the 250-watt amplifier tray.Adjust the phase adjustment caps on(A3) the phase/gain adjust module andR22, gain adjustment, on (A16) theamplifier control board for the bestcancellation.Note: Cancellation should be >20dB.Reconnect (A18) the delay line to (A7)the 7-dB UHF coupler assembly.At this point, the UHF amplifier tray isaligned, calibrated, and ready for normaloperation.5.4 IF Phase Corrector AdjustmentAs shipped, the exciter was preset toinclude linearity (gain vs. level) andphase (phase vs. level) predistortion. Thepredistortion was adjusted toapproximately compensate thecorresponding non-linear distortions ofthe amplifier trays and should need noadditional adjustments.Locate (A9) the IF phase corrector board(1227-1250) mounted in the UHF exciter.Because the amplitude correction portionof the board is not utilized in thisconfiguration, the jumper W3 on J10should be in the disable position, to +6.8VDC, and R35 and R31 should be fullyCCW. R68 is the range adjustment andshould be set in the middle of the range.The phase correction enable/disablejumper W2 on J9 should be in the enableposition to ground.Switch the video input test source toselect an NTSC 3.58-MHz modulatedstaircase or ramp test waveform and setup the station demodulator andmonitoring equipment to monitor thedifferential phase or intermodulationproducts of the RF output signal. Thereare three corrector stages on the IFphase corrector board, each with amagnitude and a threshold adjustment,that are adjusted as needed to correct forany differential phase or intermodulationproblems. If necessary, adjust the R3threshold for the cut-in point of thecorrection and the R7 magnitude for theamount of the correction.Jumper W1 on J8 is set to give thedesired polarity of the correction that hasbeen shaped by the threshold R11 andmagnitude R15 adjustments. Aftersetting the polarity, adjust the R11threshold for the cut-in point of thecorrection and the R15 magnitude for theamount of the correction that is needed.Finally, adjust the R19 threshold for thecut-in point of the correction and the R23magnitude for the amount of thecorrection that is needed.Note: Adjusting these pots changesall visual parameters and should bedone cautiously.On the IF phase corrector board (1227-1250), preset pots R7, R15, R23, andR35 fully CW and R3, R11, R19, and R31fully CCW.Set the waveform monitor to differentialstep filter and the volts/division scale to.1 volt. Center the display aroundblanking.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-16 Gradually adjust pots R3, R11, and R19CW, as needed, on the IF phase correctorboard to minimize the observed thicknessof the intermodulation as seen on thedisplay.While performing the precedingadjustments, the intermodulation beatproducts between the colorburst and theaural carrier at 920 kHz above visualcarrier should be observed on thespectrum analyzer. The frequency willvary for different video systems. Whenthe adjustments are performed properly,the intermodulation products on thespectrum analyzer should be at least -52dB down, with a red field input, frompeak visual carrier. The intermodulationdistortion, as displayed on the waveformmonitor, should be no more than 1 unitof IRE. The pot R31 on the IF phasecorrector board is used for any extraintermodulation corrections that may beneeded.Note: Any adjustment to the abovepots affects other visual parametersand some slight adjustments to all ofthe pots may be needed tosimultaneously meet all of thespecifications.5.5 Linearity Corrector AdjustmentThe IF linearity correction functionconsists of three non-linear cascadedstages, each having adjustablemagnitude and threshold, or cut-inpoints, on the ALC board. The thresholdadjustment determines at what IF signallevel the corresponding corrector stagebegins to increase gain. The magnitudeadjustment determines the amount ofgain change for the part of the signal thatexceeds the corresponding thresholdpoint. Refer to the UHF exciter trayassembly drawing (1064946) and theALC board parts location drawing (1265-5305) for the adjustments for the firstthrough third linearity corrector stages.Because the stages are cascaded, theorder of correction is important. The firststage should cut-in near white level, withthe cut-in point of the next stage towardblack, and with the last stage primarilystretching sync.To initially adjust the linearity correctors,make sure that the transmitter isoperating at full power with the desiredA/V ratio. Check that the jumper W1 onJ4 on the ALC board is enabled, betweenpins 1 and 2. Check that the ALC voltageis set to +0.8 VDC as monitored on thefront panel meter in the ALC position.Insert a modulated ramp video testsignal into the video input connector onthe remote interface panel of thetransmitter. Demodulate the outputsignal of the transmitter and observe thewaveform on a waveform monitor whilealso looking at the signal on a spectrumanalyzer. On the IF ALC board (1265-1305), preset pots R34, R37, and R40(threshold) fully CCW, and the magnitudeadjustments R13, R18, and R23 fully CW.Adjust pots R34, R37, and R40 CW onthe IF ALC board, as necessary, to givecorrection at sync or at low luminancelevels; these are viewed at the right-hand edge of the waveform monitor.If the transmitter is being driven veryhard, it may not be possible to getenough sync stretch while maintaining aflat differential gain. In this case, somevideo sync stretch may be used from thesync tip clamp on the modulator board.The sync stretch adjustment is R48 onthe sync tip clamp on the modulatorboard.Switch the transmitter to Standby.5.6 (A11) UHF High-Power TeeThe inputs to the UHF tee (1227-1017,low band; 1227-1018, mid band; or1227-1019, high band) are the outputsof the two UHF amplifier trays. Theinputs are 50-Ω impedances to match theoutput impedance of the UHF amplifiertrays. The two inputs are combined andthen sent through a piece of transmission
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-17 line, one quarter of a wavelength long, totransform the output impedance of thetee to 50Ω. The output of the UHF tee isthen sent to (A9) a bandpass waveguidefilter.Note: The bandpass filter and the(optional) trap filter are factoryswept and should not be tunedwithout the proper equipment. Donot attempt to tune the filterswithout a sweep generator or,preferably, a network analyzer. Iftuning is required, consult with theADC Field Support Departmentbefore attempting to tune the filters.5.7 (A13) Bandpass FilterThe input to the bandpass filter is theoutput of the hybrid combiner, which isthe combined output of the UHF amplifiertrays. The filter is made of aluminumwaveguide and has five resonant cavities.The filter has five bolts for tuningadjustments, three located in the middleon the left and two on the right, and fouror six rods on the front of the bandpassfilter, depending upon the channel, forcoupling adjustments between thesections. The bandpass filter also utilizestwo integral traps at -4.5 MHz and +9MHz from FV at the top and bottom,respectively, of the left-hand side of thebandpass filter, looking from the rear ofthe cabinet. Figure 5-2 shows thelocation of the bolts used for makingtuning adjustments.To tune the filter, connect a sweep signalto the input of the filter and adjust thefive tuning bolts for a 6-MHz bandwidthand a flat-frequency response across thedesired band.Note: The bandpass ripple should be≤≤≤≤0.25 dB. The 6-MHz band shouldalso have a minimum of 20 dB returnloss across the pass band.See Table 5-1 for typical bandpassvalues.Table 5-1. Typical Bandpass ValuesFREQUENCY INSERTION LOSS (dB) RETURN LOSS (dB)FV-4.5 ≥ 35FV-0.5 ≥ 20FV≤ 0.6 ≥ 20Fa≤ 0.6 ≥ 20FV+8.08 ≥ 15FV-9 ≥ 302FV≥ 30
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-18 Figure 5-2. Bandpass Filter5.8 (Optional) (A14) One- or Two-Section Trap FilterThe trap sections in the one- or two-section trap filter have been factorytuned and should not need majoradjustments. The trap filter is optionaland may not be part of this system.The input to the one- or two-section trapfilter is the output of the couplerassembly. The trap filter is comprised of3-1/8" EIA standard transmission linesections connected to the maintransmission line. The transmission lineassembly consists of 7/8" EIA standardrigid coaxial components.The traps on the output trap filter arelabeled with their center frequencyrelative to the frequency of the carrier(for example, the traps labeled -4.5 MHzare tuned for a center frequency of 4.5MHz lower than the frequency of thevisual carrier).The trap sections are reflective notchesand can be adjusted across the entireUHF frequency band. The electrical lengthof the outer sleeve and the center rod ofthe notch can be adjusted to tune thenotch frequency. The depth of the notchis set by the gap between the centerconductor of the trap section and thecenter conductor of the main line. Tightcoupling makes a deep notch, while loose
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-19 coupling makes a shallow notch. A one- section trap filter is shown in Figure 5-3.Figure 5-3. One-Section Trap Filter5.8.1 Fine TuningFine tuning of the center frequency of thenotches can be accomplished with thetuning bolts on the side of the filtersection. Loosen the nut that locks thebolt in place and adjust the bolt tochange the frequency of the notch.Monitor the output of the transmitterwith a spectrum analyzer and null thedistortion product with the bolt. Red fieldis a good video test signal to use in orderto see the +8.08-MHz product. Tightenthe nut when the tuning is completed.Hold the bolt in place with a screwdriveras the nut is tightened to prevent thebolt from slipping.5.8.2 Major TuningFor major tuning, such as changing thenotch depth or moving the notchfrequency more than 1 MHz, the outerconductor and the center conductor ofthe trap section must both be moved. AnRF sweep generator is required toperform major tuning. Apply the sweepsignal to the input of the trap filter andmonitor the output. Loosen the clampholding the outer conductor in place andlengthen the conductor to lower thefrequency of the notch or shorten it toraise the frequency of the notch. Loosenthe center conductor with an Allenwrench and move it deeper for a lower-frequency notch or out for a higher-frequency notch. These adjustmentsmust both be made to change the notchfrequency. Moving only the centerconductor or the outer conductor willeffect the notch depth and the centerfrequency. The variable that is beingadjusted with this procedure is the lengthof the center conductor inside the trapfilter. The gap between the trap and themain line should not be changed. Movingonly the inner or the outer conductorswill effect the gap and the notch depth.To only affect the notch depth, bothsections have to be moved. The notchdepth is controlled by the gap betweenthe center conductor and the trapsection. This gap also has an effect onthe center frequency. To deepen thenotch, shorten the outer conductor andpull out the center conductor until thenotch is back in the same place. Movethe sections in the opposite direction tomake a shallow notch.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-20 Note: The trap filter is typicallyadjusted for a notch depth of 10 dB. The results of tuning the output trap filterare described in Table 5-2.Table 5-2. Results of Tuning the Output Trap FilterTUNING ADJUSTMENT RESULTLengthening outer conductor only Notch frequency up, shallower notchShortening outer conductor only Notch frequency down, deeper notchInserting inner conductor deeper Notch frequency down, deeper notchInserting less inner conductor Notch frequency up, shallower notchTuning bolt in Notch frequency downTuning bolt out Notch frequency upMoving both inner and outer conductorsto keep the same gap inside Center frequency moves, notch stays thesameAfter the tuning has been completed,tighten the clamp and the Allen screwsthat hold the conductors. Use the fine-tuning bolts to bring in the frequency.The final tuning adjustments should becompleted with the transmitter drivingthe output trap filter for at least one hourto allow for warm-up drift.5.9 Phase and Gain Adjustment ofthe UHF Amplifier TraysThe following procedure was completedat the factory and should only beperformed if one of the 250-wattamplifier trays is replaced.To begin this procedure, terminate thedriver cabinet into a dummy load ratedfor at least 500 watts.Preset (A8) the line stretcher rod in therear of the driver cabinet to mid-range.Switch on the driver enable and adjustthe gain pot on the 3-watt tray for 25%Driver Output Power. Adjust the phasecontrol upward. If the % Driver OutputPower goes up, continue to adjust theline stretcher until either the peak isreached or the end-of -travel is reached.If the % Output Power goes down, push(A8) the line stretcher downward.If the end-of-travel is reached on thephase adjust as it is being movedupward, reset the phase control to mid-range and add a 2-inch length of cable tothe input of (A6) the 250-watt amplifiertray at J1. Readjust (A8) the linestretcher rod until a peak is reached oruntil end-of-travel is achieved. If end-of-travel is reached, repeat the aboveprocedure, but replace the 2-inch lengthcable with a 4-inch length of cable.If the amount of downward range runsout, add a 2-inch phase cable to theinput of (A7) the 250-watt tray and startmid-range with (A8) the line stretcher. Ifa visual power peak is reached, lockdown(A8) the line stretcher knob. If a peak isnot reached, replace the 2-inch cablewith a 4-inch cable and repeat thisprocedure.5.10 Calibration of the ForwardOutput Power Level of the AmplifierCabinetNote: Perform the followingprocedure only if the powercalibration is suspect. The amplifiercabinet output must be terminatedinto a minimum dummy load of 10kW.Switch the transmitter to Standby andperform the following adjustments, withno aural present, by removing jumpercable W1, aural IF loop-through,connected to J16 on the sync tip clampon the sync tip clamp/modulator board
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-21 (1265-1302). Connect a sync and blacktest signal to the video input jack of theUHF exciter tray. Switch the transmitterto Operate.Next, set up the transmitter for theappropriate average output power level(sync + black 0 IRE setup/wattmeter=5950 watts; sync + black 7.5 IREsetup/wattmeter=5400 watts).Note: The transmitter must have 40IRE units of sync.Adjust R28, visual and audio calibration,on (A19-A2) the visual/aural meteringboard (1161-1103) for 2 volts on FL5 onthe visual/aural metering assembly.Adjust R29 on the same board for 100%on the front panel meter in the % VisualOutput position.With the spectrum analyzer set to zerospan mode, obtain a peak reference onthe screen with the following readings:• Resolution bandwidth – maximum• Span – 0 MHz• Scale – linearReconnect jumper cable W1 to J16 on(A5) the sync tip clamp on the modulatorboard. Turn the power adjust pot on the3-watt amplifier tray front panel until theoriginal peak reference level is attained.Peak C5 for a maximum aural powerreading and then also adjust R11 for a100% aural power reading. Switch to theVisual Output Power position and adjustR39 for 100% Visual Power. Turn the 3-watt amplifier tray front panel gain potfully CCW and switch the exciter tostandby. Re-terminate the drive outputinto the diacrode cavity.5.11 Calibration of ReflectedMeteringAdjust the 3-watt amplifier tray frontpanel gain pot for 15% Visual Power onthe metering control panel. Switch S4,the power meter, to the Reflectedposition. Reverse the J6 cable and the J4termination on (A18) the final outputcoupler. Adjust R6 on (A19-A1) the singlepeak detector board (1164-1403) in thevisual/audio metering assembly for a15% Reflected Power reading. Return J4and J6 to their original positions.5.12 Board Level Adjustments5.12.1 (A1) Control Logic Board(1137-1402; Appendix B)The rear of the metering control panel isshown in Figure 5-4. The control logicboard is in the metering control paneland provides the circuitry needed for thecontrol of the automatic on/off sequenceof the transmitter and the monitoring ofthe operation of the transmitter for faultconditions. An Operate command and theinterlocks for the transmitter are alsoconnected to the board.The control logic board monitors the air-on sense, the filament-on sense, thebias-on sense, the high voltage-on sense,and the screen-on sense commandsduring each step of the automatic turn-on procedure. The board also providesthe on-command outputs in the propersequence and enables to the CommandStatus and Operating Status LEDs on thefront panel. The fault circuits monitor theoperation of the power supplies and thetube, the air flow to the tube, and thetemperature of the transmitter; theboard will shut down the transmitter ifany of these faults occur.The board supplies the air-on, filament-on, bias-on, screen-on, high voltage-on,and RF-on commands to the transmitter.In addition, the board is connected to theHigh-Voltage Enable/Disable switch toprovide commands to magnetic latchingrelay K1.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-22 Figure 5-4. Metering Control Panel (Rear)The status indicators on the board, and adescription of what each of the indicators represent when they are lit, are listed inTable 5-3.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-23 Table 5-3. Control Logic Board Status IndicatorsLED FUNCTION DESCRIPTIONDS1 OPERATE Indicates that transmitter isin the Operate modeDS2* INTLK. (INTERLOCK)Whole system shutdowninterlock used for externalconnections; normallyjumpered across on theremote control and interfaceassemblyDS3 AIRIndicates that air pressureswitch is closed and there issufficient air flow around thetubeDS4 FIL (FILAMENT) Indicates that filamentpower supply is operatingDS5 FIL UV (FILAMENT UNDERVOLTAGE)Indicates that filamentvoltage is above the presetof the lower threshold pointDS6 BIAS Indicates that bias powersupply is operatingDS7* INTLK (INTERLOCK)High-voltage shutdowninterlock; normallyjumpered across on theremote control and interfaceassemblyDS8 H.V. (HIGH VOLTAGE) Indicates that high-voltagesupply is on and above thepreset levelDS9* INTLK (INTERLOCK)Interlock is not used in the10-kW amplifier; jumperedacross on the control logicboard (J3, pins 9 and 10)DS10 RF (DRIVE)Indicates that Mutecommand has beenremoved from theupconverter trayNote: If the exciter andthe aural and visualdriver sections areoperating normally, thetransmitter will have anoutput.DS11 FAULT 3Indicates that three faultshave occurred in successionor within a given time frameNote: This action willremove the high voltage,screen, and RF drive.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-24 LED FUNCTION DESCRIPTIONDS13 VSWRIndicates that a voltagestanding wave ration thatexceeds 12.5% of reflectedpowerDS14 SCREEN Indicates that the screencurrent is greater than ±120mADS15 HVPSIndicates that the cathodecurrent exceeds 5 amps orthe high-voltage powersupply current exceeds thepreset limitDS12 GRID Indicates that the biascurrent exceeds the presetlimit of ±50 mAS1 IND. RESETWhen pushed, will only resetthe fault indicator LEDs(DS12 through DS13); willnot reset the transmitter orthe DS11 LED if lit. To resetthe DS11 LED, the faultreset switch on the frontpanel of the meteringcontrol panel must be used.* The three Interlock indicators should be lit at all times unless they are connected to anexternal sensor and a fault occurs.5.12.2 Filament Power Supply Board(1293-1304; Appendix B)The following steps will allow a thoroughtest of the software programmed into themicrocontroller and used on the filamentpower supply board (1293-1304):1. Install a pre-programmed U4, usingthe latest 1293-6316 softwareversion, into its socket on thefilament power supply board (1293-1304).2. On the filament power assembly(1299-1107), connect +12 volts toTB1-2, -12 volts to TB1-1, andground to TB1-3.3. Disconnect J3 from the filamentpower supply board (1293-1304) andturn on the external DC voltages.Verify that DS1 is blinking at a 1-Hzrate.4. Turn off the external DC voltages.Reconnect J3 to the controller board;220 VAC to TB2-1 and TB2- 2; andground to TB2-3. Connect the powersupply output to a .1-ohm, 300-wattresistor, TB2-5 to the (+) side of theresistor, and TB2-6 to the (–) side.Turn on the resistor-cooling fan.5. Turn on the external voltages;momentarily close SW1-8 and thenreopen it. Verify that J3-1 is 0.0 voltsand DS1 is blinking at a 1-Hz rate.The power supply output should be1.5 volt at this point and TB1-8should have a low voltage. Take noteof the time; a 10-minute timeoutmust be measured from powerapplication to the board.6. At this point, DS1 should be blinkingat a 1-Hz rate. Measure the voltageon TB1-7; it should be +12 volts.Measure the output voltage of the
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-25 filament power supply; it should be1.5 volts.7. Verify that J3-1 remains at 0 voltsand DS1 blinks at a 1-Hz rate whilethe following actions are performed:• Switch on SW1-3 and turn onSW1-5, SW1-6, and SW1-7individually (no time limit).• Connect +12 volts to TB1-5 forless than 5 seconds.• Turn off the external +/-12-voltpower supply for less than 5seconds.• Remove J6 from the controllerboard for less than 5 seconds.• Ground TB1-6 several times andthen leave it unconnected.• Turn off the 220 VAC at TB2-1and TB2-2 for less than 5seconds.8. After 10 minutes, DS1 should beginblinking at a 2-Hz rate. This signalsthat the 10-minute time-out periodhas successfully been completed. Atthis point, with SW1-3 on, switchSW1-5 on. J3-1 should be 0 volts.Switch SW1-5 off and SW1-6 on; J3-1 should be 4.625 volts. Switch SW1-6 off and SW1-7 on; J3-1 should be5.0 volts. If necessary, adjust R6 onthe controller board until a reading of5.0 volts is obtained.9. Ground TB1-6 to simulate a filament-on command and note the time. Thevoltage at TB1-7 should be 0 volts;220 VAC should now be present atTB2-7 and TB2-8; and DS1 should beblinking at a 4-Hz rate. The voltage atJ3-1 should increase to 4.625 voltsover a three-minute time frame.During this ramp-up phase, thefollowing conditions should not causeDS1 to stop blinking at its 4-Hz rateor the ramp-up to discontinue:• Connecting TB1-5 to +12 volts forless than 5 seconds• Turning off the external +/-12-volt power supply for less than 5seconds• Removing J6 from the controllerboard for less than 5 seconds• Turning off the 220 VAC at TB2-1and TB2-2 for less than 5 seconds• Switching SW1-5, SW1-6, andSW1-7 on and off individually (notime limit)Note: Leaving any of the aboveconditions on for longer than 5seconds should cause the filamentpower supply to revert back to the10-minute warm up cycle (J3-1 at 0volts).10. Remove the ground from TB1-6. Thevoltage at J3-1 should begin todecrease. Re-ground TB1-6. Thisshould cause J3-1 to start rampingback up. Once J3-1 is at 4.625 volts(5.2 volts across the load resistor),DS1 should not be blinking. Performall of the tasks in step 10 and verifythat J3-1 remains at 4.625 volts. Itshould be noted once again thatperforming these tasks for longerthan 5 seconds should cause thevoltage at J3-1 to again return to 0volts for 10 minutes.11. Remove the ground from TB1-6. The5 volts at J3-1 should start to rampdown. Re-ground TB1-6. The voltageat J3-1 should start to ramp back up.Remove the ground again. J3-1should return to 0 volts over a 3-minute time frame; TB1-7 shouldremain at 0 volts; TB2-7 and TB2-8should not have 220 VAC present;and DS1 should be blinking at a 4-Hzrate. Perform the same tasks as instep 10 and verify that they have noeffect on the ramp-down cycle.Taking any more than 5 seconds for
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-26 any of them should cause J3-1 toreturn to 0 volts for the 10-minutewarm-up cycle.12. Remove all of the connections to thefilament power supply assembly. Thetest is complete. 5.12.3 10-kW Bias Power SupplyBoard, 230 VAC (1181-1001;Appendix B)With the high voltage disabled,disconnect the bias cable from theTH18610 cavity assembly. Measure theDC voltage on the cable output. AdjustR14 on the bias supply board to calibratethe bias voltage on the meter on themetering control panel on the amplifierassembly.To calibrate the bias current, attach avariable power supply and currentmetering device with the (+) leadconnected to the R5/R4 junction and the(-) lead to ground. Adjust the current to10 mA and adjust R6 for a 10-mAreading on the current meter on themetering control panel.5.12.4 Screen Power Supply Board(1293-1319; Appendix B)With the high voltage enabled, and thescreen power supply breaker turned off,disconnect the screen supply cable fromthe TH18610 cavity. Turn on the screenpower supply breaker and measure thevoltage with a meter capable of at least600 VDC. Adjust R14 on the screenpower supply board (1293-1319) for 500volts. Adjust R20 on the same board for500 volts of screen power supply voltageon the metering control panel.To calibrate the screen current, turn offthe screen power supply breaker. Attacha variable power supply and currentmeasuring device with the (-) leadconnected to the R7/R8 junction and the(+) lead connected to ground. Adjust thepower supply current until a reading of10 mA is obtained on the currentmeasuring device. Adjust R9 on thescreen power supply board for a 10-mAreading on the current meter on themetering control panel. The screencurrent is now calibrated.5.12.5 Dual Polarity Fault SensingBoard (1016-1402; Appendix B)To align the screen current fault, switchoff the screen breaker and disable thehigh voltage. Attach a variable powersupply and a current meter as describedin the alignment procedures for thescreen power supply board (1293-1319)in Section 5.12.4. Adjust the current for90 mA and turn R6 until the Screen FaultLED DS14 lights. Reduce the current andDS14 should go out after fault reset S9on (A1) the control logic board (1137-1402) has been pushed.To align the screen overcurrent fault(reverse polarity), reverse the variablepower supply connections and repeat thealignment procedures for the screencurrent fault while using R12 to adjustthe trip point.To align the bias overcurrent fault, switchoff the bias supply breaker; thetransmitter will be in the Standby mode.Attach a variable power supply and acurrent meter as described in thealignment procedures for the 10-kW biaspower supply board, 230 VAC (1181-1001), in Section 5.12.3. Adjust thepower supply for a 30-mA current andadjust R25 until the Bias Current FaultLED DS12 lights. Slightly reduce thecurrent and push fault reset switch S9 on(A1) the control logic board (1137-1402).To align the bias overcurrent fault(opposite polarity), reverse the variablepower supply connections and repeat theprocedure described above while usingR18 to adjust the trip point.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-27 5.12.6 Inverting Fault Sensing Board(1016-1401; Appendix B)To align the plate overcurrent function,attach a variable power supply and acurrent meter as described in thealignment procedure for (A9) the currentmetering board (1084-1205) in Section5.12.9. Adjust the current for 5 ampsand turn R6 until the Plate Current FaultLED DS15 on (A1) the logic control board(1137-1402) lights. Slightly reduce thecurrent and push fault reset switch S9 on(A1) the control logic board (1137-1402).DS15 should go out.To align the reflected power fault, set thetransmitter for 12.5% output power.Reverse the cable at J6 and theattenuator on J5 of (A2-A2) the diacrodeoutput coupler. Adjust R12 until theVSWR Fault LED DS7 illuminates.Note: This is a 3-fault adjustment.The transmitter logic looks for thesame fault three times beforelatching in a permanent fault state.Reverse the J5 and J6 connections andclear the fault by pushing the 3-faultreset switch on the metering control frontpanel.To align the bias-on sense, the highvoltage should be enabled and thereshould be no RF drive. Adjust the biasvoltage for 2 amps static plate current.Adjust R18 until the Bias Status LEDDS18 goes out on the metering controlpanel. Return the bias voltage to theoriginal reading of 1.5 amps of staticphase current.5.12.7 Fault Sensing Board (1293-1307; Appendix B)To align the screen sense, place theexciter tray in the Standby mode. AdjustR14 on the screen power supply boardfully CCW (approximately 430 volts).Adjust R6 until the Screen Status LEDDS20 just goes out. Return R14 to 500volts screen voltage.To align the high-voltage sense, turn offCB1 and discharge all high voltage.Caution: Make sure that the high-voltage power supply cabinet issafely turned off.Remove fuse F1 from one of the high-voltage rectifier boards (A5, A6, or A7).Turn the screen breaker off and bring thetransmitter power up normally (with thehigh voltage enabled). Adjust R12 untilthe High-Voltage Status LED DS19 on themetering control panel goes out. Shutdown the transmitter and rectifier F1 onthe rectifier board while making sure thatthe high-voltage power supply cabinet issafely discharged.To align the filament ready function, setthe filament voltage to 5.2 volts. AdjustR18 until the Filament Status LED DS17just goes out and then turn the pot untilDS17 just comes back on.To align the filament undervoltage, setthe filament voltage to 5.2 volts. Placethe transmitter in the Standby mode byusing S5 on the metering control panel.At ≈5.0 volts, adjust R25 until theFilament Undervoltage LED DS5 on (A1)the control logic board (1137-1402) justgoes out. Return the transmitter toOperate. DS5 should be lit when thefilament voltage is normal (5.2 volts).5.12.8 Transmitter Control Board(1137-1003; Appendix B)To align the VSWR fault adjust on thetransmitter control board, turn thetransmitter power down to 10%. Usingthe 3-watt amplifier tray front panel gainpot, reverse the cable on J6 and theattenuator on J5 on (A2-A2) the outputcoupler. Adjust R44 until the VSWRCutback LED DS23 just begins to light onthe front panel of the metering controlpanel. Place J5 and J6 in their originalpositions.To align the output fault adjust, turn thetransmitter output power down to 10%.
10-kW UHF Transmitter with Chapter 5, Detailed Alignment ProceduresFeedforward Drive840A, Rev. 0 5-28 Adjust R38 until the RF Request LEDDS21, on the metering control frontpanel in the Operating Status section,just goes out. When the transmitteroutput power is above 10%, the LEDshould be illuminated.5.12.9 (A9) Current Metering Board(1084-1205; Appendix B)Caution: Extreme care must be takenwhen aligning the current meteringboard.First, disable the high-voltage section ofthe high-voltage power supply by turningcircuit breaker CB2 (HV) to the Offposition. Connect a variable power supplycapable of 5 amps and a currentmeasuring device across E1 (-) and E2(+) on (A9) the current metering board(1084-1205). Set the current for 4 ampson the measuring device. Adjust R3 onthe board for a 4-amp reading on thecurrent meter on the metering controlboard.This completes the detailed alignmentprocedures for the transmitter. If aproblem occurred during the alignment,refer to the detailed alignment procedurefor that tray.

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