UBS Axcera 420A Low Power Television User Manual Chapter 4

UBS-Axcera Low Power Television Chapter 4

Chapter 4

100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-1Chapter 4Detailed Alignment ProceduresIf this transmitter contains the (optional)4.5 MHz composite input kit, thebaseband video input is used when thebaseband video is connected to J2 and abaseband select is connected to J18 pins6 and 7 on the rear of the tray.Check that the RF output at J15 of thetransmitter is terminated into a dummyload of at least 100 watts. Whileperforming the alignment, refer to theTest Data Sheet for the transmitter andcompare the final readings from thefactory with the meter readings on thetray. They should be very similar. If areading is more than 10% different, aproblem with the tray may exist. Switchon the on/off AC circuit breaker on therear of the tray.4.1 Alignment of the 420ATransmitter4.1.1 Baseband SectionThis tray has adjustments for video andaudio modulation levels and other relatedparameters.Connect an NTSC composite video testsignal input (1 Vpk-pk) or an (optional)4.5 MHz composite input to thetransmitter video input jack J2 on therear of the tray.Note: J2 is a loop-through connectedto J1. It can be used as a basebandvideo source if the jumper W1 on J3of the sync tip clamp/modulatorboard is removed.Connect the baseband audio, if it isbalanced audio (+10 dBm), to theterminal block (TB1) or connect thecomposite audio (stereo) (1 Vpk-pk) tothe BNC jack (J13).Note: J13 is a loop-throughconnected to J3. It can be used as acomposite audio source if the jumperW4 on J12 of the aural IFsynthesizer board is removed.The baseband audio is not used with the(optional) 4.5 MHz composite input.Observe the front panel meter on thetray. In the video position, the meterindicates active video from ≅ 0.3V to1.0V. With an input video of 1 Vpk-pk,the display should indicate 100 IRE unitsat white. If the reading is at not theproper level, the overall video level canbe changed by adjusting the video levelcontrol (R15) on (A5) the sync tipclamp/modulator board (1265-1302).Switch the meter to the audio positionthat will indicate the audio deviation(modulation level) of the signal; themeter indicates from 0 to 100 kHz. Theaural IF synthesizer board was factoryset for ±25 kHz deviation with a balancedaudio input of +10 dBm. If the reading isnot the correct level, adjust the balancedaudio gain pot R13 on the aural IFsynthesizer board, as needed, to attainthe ±25 kHz deviation. The aural IFsynthesizer board was factory set for±75 kHz deviation with a compositeaudio input of 1 Vpk-pk. If the reading isnot correct, adjust the composite audiogain pot R17 on the aural IF synthesizerboard, as needed, for the ±75 kHzdeviation.
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-24.1.2 IF/Upconverter SectionThe upconverter section of the trayincludes adjustments for automatic levelcontrol (ALC), linearity (amplitude pre-distortion), and incidental phase (phasechange vs. level) pre-distortion forcorrection of the non-linearities of the RFamplifier section of the tray. Theupconverter section also includesadjustments to the local oscillator chaintuning and the local oscillator centerfrequency tuning. Both of thesealignments were completed at the factoryand should not need to be adjusted atthis time. Move the Operate/Standbyswitch located on the front panel of thetray to Standby.The set-up of the RF output includes anadjustment to the drive level of theamplifier section of the tray, theadjustment of the linearity, and the(optional) incidental phase predistortionwhich compensate for any nonlinearresponse of the amplifier section.Verify that all red LEDs on the ALC boardare extinguished. The following listdetails the meaning of each LED whenilluminated:• DS1 (Input fault) – Indicates thatabnormally low or no IF is present atthe input of the board• DS2 (ALC fault) – Indicates that theALC circuit is unable to maintain thesignal level requested by the ALCreference due to excessiveattenuation in the linearity or ICPMcorrector signal path or that jumperW3 on J6 is in the Manual ALC Gainposition• DS3 (Video loss) - Indicates a loss ofvideo at the input of the board• DS4 (Visual mute) - Indicates that aVisual Mute command is present (Thevisual mute is not used in thissystem.)• DS5 (Modulator Enable) - Indicatesthat the modulator output is selectedCheck that the jumper W3 on J6 of (A8)the ALC board (1265-1305) is in the Autoposition and adjust the power gain pot(R1) on the front panel of the tray toobtain +0.85 VDC on the front panelmeter in the ALC position. Move thejumper W3 on J6 to the Manual positionand adjust R87 on the ALC board for+0.85 VDC on the front panel meter inthe ALC position. Move the jumper backto Auto; this is the normal operatingposition. The detected IF signal level atJ19-2 of the ALC board is connected tothe transmitter control board. This signalsupplies the voltage to the high-bandmixer/amplifier board where it is used asan automatic gain control (AGC) for theRF output signal of the upconvertersection in the amplifier section of thetray.4.1.3 Amplifier Section of the TrayNote: Power is applied to theamplifier boards when thetransmitter is switched to Operate.Switch the transmitter to Operate andverify that the visual power reading onthe front panel meter is 100%. If not,adjust the front panel power adjust potto achieve 100%.Switch the input video test source toselect an NTSC 3.58 MHz modulatedstaircase or ramp test waveform. Set upthe station demodulator and monitoringequipment to monitor the differentialgain and phase of the RF output signal.If a synchronous demodulator having aquadrature video output is available, itcan be used with an X-Y oscilloscope todisplay incidental carrier phasemodulation (ICPM). As shipped, theexciter was preset to include linearity(gain vs. level) and incidental phase(carrier phase vs. level) predistortion.The predistortion was adjusted toapproximately compensate the
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-3corresponding non-linear distortions ofthe amplifier that is driven to place thesync level near saturation.4.1.4 Linearity Corrector AdjustmentThe IF linearity correction functionconsists of three non-linear cascadedstages, each having adjustablemagnitude and threshold, or cut-in,points. The threshold adjustmentdetermines at what IF signal level thecorresponding corrector stage begins toincrease gain. The magnitude adjustmentdetermines the amount of gain changefor the part of the signal that exceeds thecorresponding threshold point. Find theALC board on the tray level controllocations drawing (1265-5305) to locatethe adjustments for the three linearitycorrector stages. Because the stages arecascaded, the order of correction isimportant. The first stage should cut-innear white level, with the cut-in point ofthe next stage toward black, and the laststage primarily stretching sync.To adjust the linearity correctors, checkthat the IF phase corrector jumper W2 onJ9 of the IF phase corrector board isdisabled. Also check that the jumper W1on J4 of the ALC board is enabled. Selecta 3.58 MHz modulated staircase or rampinput test video signal and monitor thedifferential gain at the output of thetransmitter.Check that the ALC is set to +0.85 VDCon the front panel meter in the ALCposition. The ALC will maintain thecorresponding peak power level followingthe correctors. A positive aspect oflinearity adjustment with the ALCenabled is that the control movementswill not affect peak power.Note: The adjustment proceduremust be repeated to achieve thecorrect differential gainpredistortion.Start with the first linearity stage andadjust R34 CW on the IF ALC board tostretch the signal above the white region.Back off on the corresponding magnitudecontrol R13 as required. Next, advancethe second threshold control R37 tostretch the signal above the black rangeand then back off on the magnitudecontrol R18 as required. Adjust the thirdthreshold pot R40 to stretch sync. Backoff on the corresponding magnitudecontrol R23 as required. Go back throughthe white through black and synccorrectors to touch up the effects of ALClevel changes resulting from theadjustment.Note: If additional sync stretch isrequired, adjust R43 on the (A5)sync tip clamp/modulator board.4.1.5 IF Phase Corrector AdjustmentAs shipped, the exciter was preset toinclude linearity (gain vs. level) andincidental phase (carrier phase vs. level)predistortion. The predistortion wasadjusted to approximately compensatethe corresponding non-linear distortionsof the amplifier trays.Locate (A9) the IF phase corrector board(1227-1250). The amplitude correctionportion of the board is not utilized in thisconfiguration; as a result, the jumper W3on J10 should be in the disable positionand R35 and R31 should be fully CCW.R68 is the range adjustment and shouldbe set to the mid-point of the range. Thephase correction enable/disable jumperW2 on J9 should be in the enableposition.Switch the input video test source toselect an NTSC 3.58 MHz modulatedstaircase or ramp test waveform. Set upthe station demodulator and monitoringequipment to monitor the differentialphase or intermod products of the RFoutput signal. There are three correctorstages on the IF phase corrector board,each with a magnitude and a thresholdadjustment. They are adjusted asnecessary to correct for any differentialphase or intermod problems. Adjust the
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-4R3 threshold for the cut-in point of thecorrection and the R7 magnitude for theamount of the correction that is needed.The jumper W1 on J8 is set to give thedesired polarity of the correction shapedby the threshold R11 and magnitude R15adjustments. After setting the polarity,adjust the R11 threshold for the cut-inpoint of the correction and the R15magnitude for the amount of thecorrection that is needed. Finally, adjustthe R19 threshold for the cut-in point ofthe correction and the R23 magnitude forthe amount of the correction that isneeded.4.1.6 Calibration of the OutputPower LevelNote: Do not perform this procedureunless the power calibration issuspect.Switch the transmitter to standby. Movejumper W1 on J5 of the filter/amplifierboard, high output (1064150), to theManual position (J5-1, 2). Preset R51,the aural null pot on the visual/auralmetering board (1265-1309), full CCW.Adjust R48, the offset null pot on thevisual/aural metering board (1265-1309), for 0% visual output.Perform the following adjustments, withno aural present, by removing thejumper cable W1, the aural IF loop-through connected to J16 on (A5) thesync tip clamp/modulator board. Switchthe transmitter to Operate. Connect async and black test signal to the videoinput jack of the tray. Set up thetransmitter for the appropriate averageoutput power level on a wattmeter (sync+ black and 0 IRE setup,wattmeter=59.5 watts; sync + black and7.5 IRE setup, wattmeter=54.5 watts).Note: The transmitter output musthave 40 IRE units of sync.Adjust R28, visual calibration adjust on(A19) the visual/aural metering board,for a 100% reading on the front panelmeter in the % Visual Output position.With the spectrum analyzer set to zerospan mode, obtain a peak reference levelon the screen. Reconnect the jumpercable W1 to J16 on (A5) the sync tipclamp/modulator board. While in theVisual Output Power position, adjust L3for a Minimum Visual Power reading.Turn the gain adjust pot on the frontpanel until the original peak referencelevel is attained. Peak L1 and C8 formaximum aural power reading, thenadjust R20 for a 100% Aural Powerreading. Switch to the Visual OutputPower position and adjust R51 for 100%Visual Power.To adjust the VSWR cutback of thetransmitter, after the visual and auraloutputs are calibrated for 100%, adjustthe power to 20%, using the front panelpower adjust pot, with the jumper inmanual on the VHF filter/mixer board(1064150). Reverse the forward andreflected cables on the (A31) outputcoupler board and adjust R39 on thevisual/aural metering board for a 20%reading. Adjust R22 on the transmittercontrol board (1068933) until the frontpanel VSWR LED is illuminated. Put thecables back in the original configurationand place the transmitter in Standby.Return jumper W1 on the filter/amplifierboard, high output (1064150), to theAGC position (J5-2, 3). Use the frontpanel gain adjust pot to set all of thevoltages to .85V. If necessary, use R73on the transmitter control board to bringthe tray to 100% power.This completes the detailed alignmentprocedures for the transmitter. If aproblem occurred during the alignment,refer to the board-level alignmentprocedures that follow for more detailedinformation.
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-54.2 Board Level AlignmentProcedures4.2.1 (Optional) 4.5 MHz CompositeInput KitIf the (optional) 4.5 MHz composite inputkit is purchased, the tray is capable ofoperating by using either the 4.5 MHzcomposite input or the baseband audioand video inputs. The kit adds the (A24)composite 4.5 MHz filter board (1227-1244) and the (A25) 4.5 MHz bandpassfilter board (1265-1307). When the 4.5MHz intercarrier signal generated by the4.5 MHz composite input has beenselected by the 4.5 MHz composite inputkit, the 4.5 MHz generated by the auralIF synthesizer board is not used. Whenthe 4.5 MHz intercarrier signal generatedby the baseband video and audio inputswith baseband has been selected by the4.5 MHz composite input kit, thecomposite 4.5 MHz filter board and the4.5 MHz bandpass filter board are notused.The tray has been factory tuned andshould need no alignments to achievenormal operation. To align the tray forthe 4.5 MHz composite input, apply the4.5 MHz composite input, with the testsignals used as needed, to the videoinput jack (J1 or J2 [loop-throughconnections]) on the rear of the tray.Select the 4.5 MHz composite input byremoving the baseband select from J18-6and J18-7 on the rear of the tray.To align the exciter using baseband videoand audio inputs, apply the basebandvideo, with the test signals used asneeded, to the video input jack (J1 or J2[loop-through connections]) and thebaseband audio to the proper basebandaudio input on the rear of the tray. Forbalanced audio input, connect TB1-1(+),TB1-2(-), and TB1-3 (GND). Forcomposite/stereo audio, connect thecomposite audio input jack (J3 or J13[loop-through connections]) and connecta baseband select from J18-6 and J18-7on the rear of the tray.4.2.2 Delay Equalizer Board (1227-1204)The jumper W1 on J5 of the sync tipclamp/modulator board, if present, mustbe in the Enable position between pins 2and 3.Note: This board has been factorytuned and should not be retunedwithout the proper equipment.To tune this board:1. Connect a sinX/X test signal intojack J1-2 on the delay equalizer board.2. Monitor the video output of theboard, at the video sample jack J2,with a video measuring set, such asthe VM700, 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 out of theboard as into the board.4.2.3 (A24) Composite 4.5 MHz FilterBoard (1227-1244)This board is part of the 4.5 MHz input kitand will only function properly with a 4.5MHz composite input signal and the 4.5MHz composite input selected. To alignthis board:1. Connect the test signal from anenvelope delay measurement set tothe video input of the tray at J1 orJ2.2. Connect an oscilloscope to jack J7,video out, between J7 center pinand pin 1 or 3 ground. Adjust C21,frequency response, if needed forthe best frequency response.Adjust R32, video gain, for a signal
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-6level of 1 Vpk-pk on theoscilloscope.The output at J6 and J7 on the boardshould be video only, without the 4.5MHz aural subcarrier.4.2.4 (Optional) (A25) 4.5 MHzBandpass Filter Board (1265-1307)This board is part of the 4.5 MHz input kitand will only function properly with a 4.5MHz composite input signal and the 4.5MHz composite input selected. To alignthis board:1. Adjust the filter with L2, C3, L4,and C7 for a frequency response ofno greater than ±0.3 dB from 4.4to 4.6 MHz.2. Adjust C19 for an overall peak-to-peak variation of less than ±0.3 dBfrom 4.4 MHz to 4.6 MHz.3. Recheck the frequency response; itmay have changed with theadjustment of the envelope delay.If necessary, retune the board. 4.2.5 (A7) IF Carrier Oven OscillatorBoard (1191-1404)To align this board: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, which is theaural phase lock loop reference.4.2.6 (A5) Sync TipClamp/Modulator Board (1265-1302)To align this board:1. Determine if jumper W4 on jack J3is present. Jumper W4 terminatesthe video input into 75Ω. Removejumper W4 if a video loop-throughis required on the rear chassis atjacks J1 and J2.2. Set the controls R20, the white clip,R24, the sync clip, and R45, thesync stretch cut-in, to their fullcounter clockwise (CCW) position.Set R48, the sync magnitude, fullyCW and place the jumper W7 onjack J4 to the clamp off, disable,position.3. Connect a 5-step staircase videotest signal to the input of thetransmitter.4. Monitor TP2 with an oscilloscope.Adjust R12, the video gain pot, for1 Vpk-pk.5. Change the video input test signalto a multiburst test pattern. Whilemonitoring TP2, adjust C8 and R32for a flat frequency response.Change the input video test signalback to the 5-step staircase.6. Monitor TP2 with an oscilloscope.Adjust the pot R41, manual offset,for a blanking level of -0.8 VDC.The waveform shown in Figure 4-1should be observed. Move thejumper W2 on J4 to the clampenable position. Adjust the potR152, depth of modulation, for ablanking level of -0.8 VDC.Note: This waveform represents thetheoretical level for propermodulation depth. Step 9 belowdescribes how to set the modulationdepth through the use of a televisiondemodulator or a zero-spannedspectrum analyzer tuned to thevisual IF frequency.
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-7Figure 4-1. Waveform7. The following test setup is for theadjustment of the depth ofmodulation and ICPM at IF:A. Remove the cable that is onJ18 and connect the doublesideband 45.75 MHz visual IFsignal from J18 to a 10 dBsplitter/coupler. Connect thecoupled port of thesplitter/coupler to the RF inputof a television demodulator.Connect the direct port to aspectrum analyzer.B. Connect the 75Ω video outputof the demodulator to the videoinput of a waveform monitor.For ICPM measurements, alsoconnect the quadrature outputof the demodulator to thehorizontal input of thewaveform monitor using a 250kHz low pass filter. (Anoscilloscope can be used inplace of a waveformmonitor).C. Set the controls of thedemodulator to the following:Detector mode – ContSound trap – InZero carrier – OnAuto – SyncAudio source – SplitDe-emphasis – In8. Move the jumper W7 on J4 to theclamp disable position. Readjust thepot R41, manual offset, for thecorrect depth of modulation byobserving the demodulatedwaveform on the waveform monitoror on the spectrum analyzer set tozero span.9. Check the demodulated video forproper sync to video ratio (sync is28.6% of the total white videosignal). 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, ifneeded, for the correct depth ofmodulation.10. Move the jumper W7 on J4 to theclamp enable position. Readjust thepot R152, depth of modulation, forthe correct depth of modulation.11. Set the waveform monitor todisplay ICPM. Preset R53 full CCW,adjust C78 for the greatest effect atwhite on the ICPM display, and thenadjust R53 for minimum ICPM.12. Recheck the depth of modulationand, if necessary, adjust R152,depth of modulation.
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-813. On a spectrum analyzer, adjust thepot R70 for a level of approximately-10 dBm at J18.14. Remove the input video test signal.Place the front panel meter in thevideo position and, while monitoringthe meter, adjust pot R144, zeroadjust, for a reading of zero.15. Replace the input video testsignal (the 5-step staircase).Turn the front panel meter tothe video position and adjustR20 on the transmitter controlboard for a reading of 1V (10on the 0-10 scale). This boarddoes not have sync metering.16. Reconnect the plug to J18 andmove the spectrum analyzer testcable to the 41.25 IF output jackJ16. Tune C59 and L17-L20 tomaximize the 41.25 MHz aural IFsignal and minimize the out-of-band products. Adjust pot R97 for -20 dBm at J16.17. Reconnect the plug to J16 andmove the spectrum analyzer testcable to the IF output jack J20.Preset R62, the visual IF gain pot,to the middle. Insert a multibursttest signal into the transmitter andobserve the visual frequencyresponse with the spectrumanalyzer set at 1 dB/division. TuneR63 and C30, the IF frequencyresponse adjustments, for a flatfrequency response (±0.5 dB).18. While still monitoring J20 with aspectrum analyzer, readjust R62,visual IF gain, for a 0 dBm visualoutput level. Adjust R85, A/V ratio,for a minus 10 dB aural-to-visualratio or to the desired A/V ratio.Reconnect the plug to J20.19. Using an input video test signal (the5-step staircase) with 100 IREwhite level, monitor TP2 with anoscilloscope. Set the control R24,the sync clip, just below the pointwhere sync clipping begins to occur.Similarly, set R20, the white clip, tojust below the point at which thewhite video begins to clip.4.2.7 (A4) Aural IF SynthesizerBoard, 4.5 MHz (1265-1303)1. To set up the test equipment forthis board:A. Connect the 600Ω 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 (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. At the front of thedemodulator, connect a shortcable from the RF-out jack tothe IF-in jack.D. Connect a cable from the 600Ωaudio 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 kHzResolutionbandwidth – 3 kHzTime/Division – 50 msec
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-9Trigger – 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 (THD=< 0.5%).6. Disconnect the 600Ω balancedaudio input to the tray. Connect a75Ω stereo audio input (400 Hz at 1Vpk-pk) to the composite audioinput jack J3 on the rear of thetray. Follow the procedure in thestereo generator instruction manualfor matching the level of thegenerator to the exciter. Use R17 toadjust the composite audio gain.7. Check the distortion level on thedistortion analyzer (THD)=< 0.5%) 4.2.8 (A8) ALC Board (1265-1305)(Part 1 of 2)Table 4-1 describes the functions of eachLED on the ALC board (A8).Table 4-1. ALC Board LEDsLED FUNCTIONDS1 (Red LED) Indicates that an abnormally low IF signallevel is present at IF input connector J1DS2 (Red LED) Indicates that the ALC circuit is unable tomaintain the level requested by the ALCreference due to excessive attenuation inthe linearity, the IF phase corrector signalpath, or the jumper W3 on J6 is in manualgainDS3 (Red LED) Indicates a video loss faultDS4 (Red LED) Indicates that a Mute command is presentDS5 (Green LED) Indicates that the output from themodulator is selected as the input to theboard1. To align the ALC board, preset thefollowing controls in the tray:A. ALC Board (1265-1305)Connect jumper W1 on J4 todisable, between pins 2 and 3 (todisable linearity correctors).Connect jumper W3 on J6 tomanual, between pins 2 and 3 (formanual gain control).Adjust R87, manual gain pot, tomid-range.B. IF Phase Corrector Board (1227-1250)Move W2 on J9 to phasecorrection: enable. Move W3 onJ10 to amplitude correction:disable.2. The combined IF output of the synctip clamp modulator board is cabledto jack J32 of the ALC board.Remove J32 from the board, andlook to see if DS1, input fault, isilluminated. Reconnect J32 andobserve that DS1 is extinguished.
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-103. 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 flatfrequency response of ±0.5 dB.5. Before proceeding with the secondpart of the ALC board alignment,check to see that the IF phasecorrector board (1227-1250) isfunctioning properly.4.2.9 (A9) IF Phase Corrector Board(1227-1250)Refer to Section 4.1.5 of this chapter forthe system alignment procedures for theIF phase corrector board. 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 the J3 IF O/Pjack of the ALC board (A8).The IF output jack of the IF phasecorrector board is fed to the J7 IF I/Pjack of the ALC board (A8).4.2.10 (A8) ALC Board, NTSC (1265-1305) (Part 2 of 2)To align this board:1. Input a multiburst video test signal.Connect a spectrum analyzer toJ11. Tune C63 for a flat frequencyresponse of ±0.5 dB.2. Move the Operate/Standby switchon the front panel to the Operateposition.3. Place jumper W3 on jack (J6) in theManual mode and adjust R87 for0.5 volts at TP4.4. Place jumper W3 on J6 in the Automode and adjust the front panelpower adjust control A20 fullclockwise (CW). If the (optional)remote power raise/lower kit ispresent, then adjust switch S1 onthe board to maximum voltage atTP4. Adjust R74, the range adjust,for 1 volt at TP4.5. Adjust the front panel power adjustcontrol A20 for 0.5 VDC at TP4. Ifthe (optional) remote powerraise/lower kit is present, adjustswitch S1 on the board to midrangeand then adjust the front panelpower adjust control (A20) for 0.8VDC at TP4.6. Disconnect the plug that is on J12(IF output) and monitor J12 with aspectrum analyzer. Verify an outputof approximately 0 dBm. Ifnecessary, adjust R99 to increasethe output level. If less output levelis needed, move the jumpers J27and J28 to pins 2 and 3 and thenadjust R99. Reconnect J12.7. Move W2 on J5 to the cutbackenable position. Remove the inputvideo signal and verify that theoutput of the transmitter drops to25%. Adjust R71, the cutback level,if necessary. Restore the inputvideo.Note: The following step affects theresponse of the entire transmitter.8. Connect a video sweep signal to theinput of the tray. Monitor theoutput of thesystem with a spectrum analyzer.Adjust C71 with R103 and C72 withR106 as needed to flatten theresponse. C71 and C72 adjust forthe frequency of the correctionnotch being applied to the visualresponse of the transmitter. R103and R106 are used to adjust thedepth and width of the correctionnotch.9. Refer to the Section 4.1.4 of thischapter for the system alignmentprocedures for the linearity
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-11correctors. Controls R13, R18, andR23, the magnitude controls,should be set full CW. Controls R34,R37, and R40 are the linearity cut-in adjustments.4.2.11 (A14-A1) Channel OscillatorBoard (1145-1201)This board is mounted in (A14) thechannel oscillator assembly (1145-1202).To align the board:1. Connect the main output of thechannel oscillator (J1) to aspectrum analyzer, tuned to thecrystal frequency, and peak thetuning capacitors 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 DVM to TP1 onthe x4 multiplier board. Tunecapacitors C6 and C18 formaximum voltage, then also tuneL2 and L4 for maximum voltageoutput at TP1.2. Connect the sample output of thechannel oscillator (J2) to a suitablecounter and tune C11, coarseadjust, and C9, fine adjust, to thecrystal frequency.Note: Do not repeak C6, C18, L2, orL4. This may change the outputlevel.Note: While adjusting C9 and C11 tothe crystal frequency, the peakvoltage monitored at TP1 of the x4multiplier board should notdecrease. If a decrease doesoccur, there may be a problem withthe crystal. Contact ADCTelecommunications Field Supportfor further instructions.Note: If the VCXO board (1145-1204) in the VCXO assembly (1145-1206) is used, the C9 fine frequencyadjust is not located on the VCXOboard. Use R9 on the FSK w/EEPROMboard.3. Reconnect the main output (J1) ofthe channel oscillator to the input(J1) of the x4 multiplier.4.2.12 (A15-A1) x4 Multiplier Board(1174-1112)While monitoring the board with a DCvoltmeter, maximize each test pointvoltage by tuning the broadbandmultipliers in the following sequence:1. Monitor TP1 with a DVM and tuneC4 for maximum voltage. MonitorTP2 with a DVM and tune C6 andC10 for maximum voltage.Monitor TP3 with a DVM and tuneC12; repeak C4, C6, and C10 formaximum voltage.2. Connect a spectrum analyzer,tuned to four times the crystalfrequency, to the x4 multiplieroutput jack (J2). While trying tokeep the out-of-band products toa minimum, monitor the outputand peak the tuning capacitors formaximum output.The output of the x4 multiplier connectsto (A11-A1) the filter/mixer board.4.2.13 (A11-A1) Filter/Mixer Board(1150-1102)To align the board:1. Monitor J4, the LO output of theboard, with a spectrum analyzerand adjust C12 and C18 formaximum output (+14 dBm) atthe LO frequency.2. Adjust C13 and C17 for the bestfrequency response for the LOfrequency.
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-124.2.14 (A11-A2) Filter/AmplifierBoard, High Output (1064150)The filter/amplifier board has beenfactory swept and adjusted for a 6 MHzbandwidth.Note This board should not be tunedwithout the proper equipment.The filtered output connects to J1 of theboard and is amplified by U1 to anominal +11 dBm visual and +1 dBmaural level by adjusting R9. The output isfed to the (A23-A1) high-band amplifierboard (1218-1201) mounted on the VHFamplifier heatsink assembly (A23). 4.2.15 (A23-A1, A23-A3, A23-A4)High-Band Amplifier Boards (1218-1201)Each of the high-band amplifier boardshas 20 dB of gain. A23-A1 is biased at 2amps of idling current with no RF driveapplied. A23-A3, A4 are biased at 1.5amps each, with no RF drive applied. Toset the bias for the final amplifier board(A23-A1), the RF drive will need to beremoved. To monitor the currentadjustment, read the voltage drop acrossthe 3-watt resistor, R5, mounted on theovercurrent protection board (1273-1130). Using Ohm’s Law, determine thevoltage drop across the resistor (2 ampsx 0.01Ω=0.020 volts). Preset the biasadjust pots R5 and R9 CCW. Slowlyadjust the bias adjust pot R5 for 1 ampon the meter and then adjust R9 for 2amps total current on the meter.To set the bias for the final amplifierboard (A23-A3), the RF drive will need tobe removed. To monitor the currentadjustment, read the voltage drop acrossthe 3-watt resistor, R6, mounted on theovercurrent protection board (1273-1130). Using Ohm’s Law, determine thevoltage drop across the resistor (1.5amps x 0.01Ω=0.015 volts). Preset thebias adjust pots R5 and R9 CCW. Slowlyadjust the bias adjust pot R5 for .75amps on the meter and then adjust R9for 1.5 amps total current on the meter.To set the bias for the final amplifierboard (A23-A4), the RF drive will need tobe removed. To monitor the currentadjustment, read the voltage drop acrossthe 3-watt resistor, R7, mounted on theovercurrent protection board (1273-1130). Using Ohm’s Law, determine thevoltage drop across the resistor (1.5amps x 0.01Ω=0.015 volts). Preset thebias adjust pots R5 and R9 CCW. Slowlyadjust the bias adjust pot R5 for .75amps on the meter and then adjust R9for 1.5 amps total current on the meter.4.2.16 Frequency Adjustment of theHigh-Band Amplifier BoardsThe following procedures describe how toadjust these boards:Move the ALC/manual jumper on the(A11-A2) filter/amplifier board to themanual position, disabling the ALCcircuit. Remove two fuses (F2 and F3) onthe overcurrent protection board todisable the (A23-A3 and A4) high-bandamplifier boards. Connect a spectrumanalyzer to output connector J2 on the(A23-A1) high-band amplifier board.Adjust C9 and C19 for peak power andfrequency response.Move the spectrum analyzer to theoutput connector J2 on the (A23-A3)high-band amplifier board. Install fuse F2and adjust C9 and C19 (on the [A23-A3]high-band amplifier board) for peakpower and frequency response.Move the spectrum analyzer to theoutput connector J2 on the (A23-A4)high-band amplifier board. Remove fuseF2, install fuse F3, and adjust C9 andC19 (on the [A23-A4] high-bandamplifier board) for peak power andfrequency response.Move the spectrum analyzer to theoutput, J2, of the (A23) amplifierheatsink assembly. Install all of the fusesand readjust C9 and C19, if needed, on
100 Watt High Band VHF Transmitter Chapter 4, Detailed Alignment Procedures420A, Rev. 0 4-13all three amplifier boards for peak powerand frequency response.4.2.17 (A29) Overcurrent ProtectionBoard (1273-1130)There are no adjustments to this board.4.2.18 (A19) Visual/Aural MeteringBoard (1265-1309)The board is calibrated to give a peakdetected output indication to the frontpanel meter for % Visual Output, %Aural Output, and % Reflected Outputand should not be adjusted. If necessary,refer to Section 4.1.2 of this chapter forthe alignment procedures for the frontpanel meter.4.2.19 (A3) +12 VDC (4A)/-12 VDC(1A) Power Supply Board (1265-1312)There are no adjustments to this board.DS1 will be lit if a +12 VDC output isconnected to J6. DS2 will be lit if a +12VDC output is connected to J3. DS3 willbe lit if a +12 VDC output is connected toJ4. DS4 will be lit if a +12 VDC output isconnected to J5. DS5 will be lit if a -12VDC output is connected to J7 and J8.4.2.20 (A31) Output Coupler Board(1211-1004)There are no adjustments to this board.This completes the detailed alignmentprocedures for the boards in the 420Atransmitter.

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