UBS Axcera 835-3 UHF television transmitter User Manual Chapter 4

UBS-Axcera UHF television transmitter Chapter 4

Chapter 4

3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-1Chapter 4Detailed Alignment ProceduresBefore beginning the alignment procedures, make sure that the RF output at J2 of (A11)the output coupler assembly of the transmitter is terminated into a dummy load of atleast 3000 watts. While performing the alignment, refer to the test data sheet for thetransmitter and compare the final readings from the factory with the readings on eachof the trays. The readings should be very similar. If one of the readings is off by asignificant degree, the problem is likely to be in that tray.Switch on the UHF exciter tray circuit breaker on the AC distribution panel in the UHFexciter cabinet and the circuit breaker on the rear of the UHF exciter tray for the 3-kWtransmitter. Also switch on the main and the individual amplifier circuit breakers on theAC distribution panel in the amplifier array cabinet.4.1 (A1) UHF Exciter Tray (1227-1200; Appendix A)The (A1) UHF exciter tray has been factory tuned and should need no alignment toachieve normal operation. Apply the baseband video and audio inputs of the test signals,as needed, to the A/V input and remote interface panel on the rear of the transmitter. 4.1.1 (Optional) (A6) Delay Equalizer Board (1227-1204; Appendix B)This board may not be present in the tray.This board has been factory tuned and should not be re-tuned without the properequipment. To align this board:• Connect a sinX/X test signal into jack J1-2 on the delay equalizer board.• Monitor the video output of the board at video sample jack J2 with a videomeasuring set VM700 adjusted to measure group delay.• Tune the four stages of the board using the variable inductors (L1-L4) andpotentiometers (R7, R12, R17, and R22) until the signal attains the FCC group delaycurve. The stages are arranged in order of increasing frequency. Adjust R29, ifneeded, for the desired video gain.4.1.2 (A7) IF Carrier Oven Oscillator Board (1191-1404; Appendix B)While monitoring J3 with a spectrum analyzer, observe the 45.75 MHz visual IF (+5dBm).Connect a frequency counter to J3 and adjust C17 for 45.750000 MHz.Connect a frequency counter to J1 and check for 50 kHz; this is the aural phase lockloop reference.4.1.3 (A5) Clamp/Modulator Board (1227-1208; Appendix B)Determine if jumper W1 on jack J3 is present. Jumper W1 terminates the video inputinto 75 ohms. Remove jumper W1 if video loop-through is required on the rear chassisjacks J1 and J2.
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-2Set the controls R28, the white clip; R31, the sync clip; and R43, the sync stretch, totheir fully counter-clockwise (CCW) position. Note: On Revision 6 or later boards, controls R43, sync stretch cut-in, andR176, sync stretch magnitude, should be set fully CCW.Place jumper W5 on jack J11 to the clamp disable position (towards the top of theboard) and jumper W2 on jack J4 to the AGC disable (out) position.Connect a 5-step staircase video test signal to the input of the transmitter.Monitor TP5 (on Revision 1 or later boards) with an oscilloscope. Adjust R15, the videogain pot, for 1 Vpk-pk. Alternately, pin 2 on video sample jack J7 can be monitored for 1Vpk-pk when terminated into 75 ohms (2 Vpk-pk when unterminated).Change the video input test signal to a multiburst test pattern. While monitoring TP5 orvideo sample jack J7, pin 2, adjust C8 and R35 for a flat-frequency response. Changethe input video test signal back to the 5-step staircase.Decrease the amplitude of the input video test signal (the 5-step staircase) to 0.5 Vpk-pk. (Double terminating the input will accomplish the required level reduction or R15can be adjusted as needed.) Monitor pin 2 of IC U8B (or TP6 on Revision 1 or laterboards) with an oscilloscope. Adjust R76, the sync separator, to obtain a steadywaveform as shown in Figure 4-1.Figure 4-1. Steady Waveform Obtained When R76 is AdjustedMonitor pin 9 of IC U9 with an oscilloscope. The waveform shown in Figure 4-2 shouldbe observed.Figure 4-2. Waveform Observed When Pin 9 of IC U9 is Monitored
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-3Monitor pin 13 of IC U6 (or TP7 on Revision 1 or later boards) with an oscilloscope. Thewaveform shown in Figure 4-3 should be observed.Figure 4-3. Waveform Observed When Pin 13 of IC U6 is MonitoredRestore the input video level to 1 Vpk-pk.Monitor TP5 (on Revision 1 or later boards) or pin 2 of J7 (terminated into 75 ohms)with an oscilloscope. Adjust pot R105, manual bias, for a blanking level of -0.8 VDC. Thewaveform shown in Figure 4-4 should be observed. Move jumper W5 on J11 to theclamp enable position (towards the bottom of the board). Adjust pot R95, clamp bias, fora blanking level of -0.8 VDC. Again, the waveform in Figure 4-4 should be observed.Figure 4-4. Waveform Observed When An Adjustment is Made for a Blanking Level of –0.8 VDCNote: The waveform in Figure 4-4 represents the theoretical level for propermodulation depth. The second step below explains how to set the modulationdepth by the use of a television demodulator or a zero-spanned spectrumanalyzer tuned to the visual IF frequency.Connect the oscilloscope to the lead of L4 that is closest to C32 and adjust the colornotch subcarrier trap, C32, until the 3.58-MHz color burst is nulled.Check the ratio of sync to video (0.286 volts of sync for a 1 Vpk-pk total video signal). Ifnecessary, adjust R43, the sync stretch cut-in (on Revision 6 or later boards, also adjustR176, the sync stretch magnitude) for the proper sync ratio. Re-adjust R15, the videogain pot, as described above, to maintain a 1 Vpk-pk video signal.To construct the test setup for the adjustment of the depth of modulation and ICPM atIF:• Remove the cable on J18 and connect the double sideband 45.75-MHz visual IFsignal from J18 to a 10-dB splitter/coupler. Connect the coupled port of the
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-4splitter/coupler to the RF input of a television demodulator. Connect the direct portto a spectrum analyzer.• Connect the 75-ohm video output of the demodulator to the video input of awaveform monitor. For ICPM measurements, also connect the quadrature output ofthe demodulator to the horizontal input of the waveform monitor using a 250-kHzlow pass filter (an oscilloscope can be used in place of a waveform monitor).• Set the controls of the demodulator to the following:Detector mode – ContSound Trap – InZero Carrier – OnAuto – SyncAudio Source – SplitDe-emphasis – InMove jumper W5 on J11 to the clamp disable position. Re-adjust pot R105, manual bias,for the correct depth of modulation by observing the demodulated waveform on thewaveform monitor or on the spectrum analyzer set to zero span. Move jumper W5 on J11 to the clamp enable position. Re-adjust pot R95, the clampbias, for the correct depth of modulation.Set the waveform monitor to display ICPM. Preset R143 fully clockwise (CW) and adjustC65 for the greatest effect at white on the ICPM display. Adjust R143 for minimumICPM.Recheck the depth of modulation and adjust R95, clamp bias, if necessary.Remove the video input signal. Alternately, turn the front panel meter switch betweenthe video and sync positions and adjust blanking pot R49 for a reading of zero on bothpositions on the front panel meter.Replace the input video test signal (the 5-step staircase). While monitoring the frontpanel meter in the sync position, adjust R19 on the transmitter control board (1227-1209) for a reading of 40 (4 on the 0 to 10 scale). Turn the front panel meter to thevideo position and adjust R20 on the transmitter control board for a reading of 100 (10on the 0 to 10 scale).Place jumper W2 on jack J4 to the AGC enable position. Adjust R60, the sync level, forthe proper depth of modulation in the AGC mode. Return jumper W2 on jack J4 to theAGC disable position.Note: Use the AGC mode only if the incoming program video level cannot beproperly maintained.Reconnect the plug to J18 and move the spectrum analyzer test cable to 41.25 IF outputjack J16. Tune C56 and L10 to L13 to maximize the 41.25-MHz aural IF signal andminimize the out-of-band products.Reconnect the plug to J16 and move the spectrum analyzer test cable to IF output jackJ20. Preset R150, the visual IF gain pot, to the middle of the range. Insert a multibursttest signal into the transmitter and observe the visual frequency response with the
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-5spectrum analyzer set at 1 dB/division. Tune R153 and C77, the IF frequency responseadjustments, for a flat-frequency response (±0.5 dB).While still monitoring J20 with a spectrum analyzer, re-adjust R150, visual IF gain, for a0-dbm visual output level. Adjust R127, A/V ratio, for a –13-dB aural-to-visual ratio orto the required A/V ratio. Reconnect the plug to J20.Using an input video test signal (the 5-step staircase) with 100-IRE white level, monitorTP5 or video sample jack J7, pin 2, with an oscilloscope. Set control R31, the sync clip,just below the point where sync clipping begins to occur. Similarly, set R28, the whiteclip, to the point just below where the white video begins to clip. Note: This procedure should be checked after system setup or if linearity problemsoccur.4.1.4 (A4) Aural IF Synthesizer Board (1227-1205; Appendix B)To set up the test equipment for this board, begin by connecting the 600-ohm balancedaudio output from an audio oscillator to the balanced audio input jack of the transmitter,J4-2 (+), J4-3 (-), and J4-1 (ground), on the A/V input and remote interface assemblyof the transmitter.Connect the aural IF output at J16 on the clamp modulator board to the input of an IFsplitter. Connect one output of the splitter to the video demodulator and the otheroutput to the spectrum analyzer.Connect a short cable at the front of the demodulator from the RF out jack to the IF injack.Connect a cable from the 600-ohm audio output jack of the demodulator to the input ofan audio distortion analyzer.Set the output frequency of the audio oscillator to 400 Hz and the output level to +10dBm.Center the aural carrier on the spectrum analyzer with the spectrum analyzer set to thefollowing:Frequency/Division – 10 kHzResolution bandwidth – 3 kHzTime/Division – 50 msecTrigger – Free runAdjust L5 for approximately +3.5 VDC on the cathode of CR17. The green LED DS1should be illuminated, indicating a locked condition. If not, re-tune L5 for a lockedcondition.Adjust R13 on the aural IF synthesizer board for ±25-kHz deviation.Check the distortion on the aural distortion analyzer (S/B =< 0.5%).Disconnect the 600-ohm balanced audio input to the tray. Connect a 75-ohm stereoaudio input (400 Hz at 1 Vpk-pk) to composite audio input jack J6 on the A/V input andinterface assembly. Follow the procedure in the stereo generator instruction manual for
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-6matching the level of the generator to the exciter. R17 adjusts the composite audiogain.Check the distortion level on the distortion analyzer (S/B =< 0.5%).4.1.5 (A8) ALC Board (1227-1207; Appendix B) (Part 1 of 2)The following explains the meaning of each LED on (A8) the ALC Board when they areilluminated:• DS1 - Indicates that an abnormally low IF signal level is present at IF inputconnector J1• DS2 - Indicates that the ALC circuit is unable to maintain the signal level requestedby the ALC reference; this is usually due to excessive attenuation in the linearity orthe IF phase corrector signal path, or switch S1 is in the Manual Gain mode• DS3 - Indicates a video fault• DS4 - Indicates that a Mute command is presentTo align the ALC board, preset the following controls in the UHF exciter tray:• ALC Board – To disable linearity correctors: jumper W1 on J4 to Disable mode(towards the bottom of the board); for manual gain control: jumper W3 on J6 toManual mode (towards the top of the board); R87, the manual gain pot, adjusted tomid-range• IF Phase Corrector Board – W2 on J9 in phase correction enable; W3 on J10 inamplitude correction disableThe combined IF output of the clamp modulator board is cabled to jack J1 of the ALCboard. Remove J1 from the board, and look to see that DS1, the Input Fault LED, isilluminated. Reconnect J1 and check to see that DS1 is extinguished.Jumper W3 on J6 should be in the Manual position (towards the top of the board).Monitor jack J3, IF output, with a spectrum analyzer and adjust R87 for approximately a–20-dBm level.With a multiburst video signal present, tune C4 for a flat-frequency response of±0.5 dB.Before proceeding with the second part of the ALC board alignment, check the IF phasecorrector board to make sure that it is functioning properly.4.1.6 (A9) IF Phase Corrector Board (1227-1250; Appendix B)Refer to the alignment procedure for the setup of the IF phase corrector board.The IF input jack of the IF phase corrector board is fed from J3, the IF output jack of(A8) the ALC board. The IF output jack is fed to J7, the IF input jack of the ALC board.4.1.7 (A8) ALC Board (1227-1207; Appendix B) (Part 2 of 2)
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-7Input a multiburst video test signal. Remove the plug from J8 and connect a spectrumanalyzer. Tune C63 for a flat-frequency response of ±0.5 dB. Reconnect the plug to J8.Move the Operate/Standby switch on the front panel to the Operate position. Place jumper W3 on jack J6 in the Manual mode (towards the top of the board) andadjust R87 for 0.8 volts at J19, pin 2, or at TP4.Place jumper W3 on J6 in the Auto mode (towards the bottom of the board) and adjustfront panel power adjust control A20 fully CW. If the optional remote power raise/lowerkit is present, adjust switch S1 on the board to maximum voltage at J19, pin 2, or atTP4. Adjust R74, the range adjust, for 1 volt at TP4.Adjust front panel power adjust control A20 for 0.8 VDC at J19, pin 2, or at TP4. If theoptional remote power raise/lower kit is present, adjust switch S1 on the board to themid-range of its travel. Adjust front panel power adjust control A20 for 0.8 VDC at TP4.Disconnect the plug that is now on J12 (IF output) and monitor it with a spectrumanalyzer. Verify an output of approximately 0 dBm. Adjust R99, if needed, to increasethe output level. Reconnect the plug on J12.Move W2 on J5 to the cutback enable position (towards the bottom of the board).Remove the input video signal and verify that the transmitter output drops to 25%.Adjust R71, the cutback level, if necessary. Restore the input video.Note: The following step affects the response of the entire transmitter. Connect a video sweep signal to the input of the transmitter. Monitor the output of thesystem with a spectrum analyzer. Adjust C71 with R103 and C72 with R106, as needed,to flatten the response. C71 and C72 adjust for the frequency of the correction notchbeing applied to the visual response of the transmitter. R103 and R106 are used toadjust the depth and width of the correction notch.Refer to the alignment procedures for the setup of the linearity correctors. ControlsR13, R18, and R23, the magnitude controls, should be set fully CW. Controls R34, R37,and R40 are the linearity cut-in adjustments. 4.1.8 (A11-A1) UHF Upconverter Board (1227-1237; Appendix B)This board is mounted in (A11) a UHF upconverter enclosure assembly (1227-1238).R10 is a gain control that is adjusted to give an approximately +17-dBm output at J5 ofthe board.4.1.9 (A14-A1) Channel Oscillator Board (1145-1201; Appendix B)This board is mounted in (A14) the channel oscillator assembly (1145-1202).To align this board, begin by connecting the main output of the channel oscillator, J1, toa spectrum analyzer, tuned to the crystal frequency, and peak the tuning capacitors C6and C18 for maximum output. Tune L2 and L4 for maximum output. The output levelshould be about +5 dBm. The channel oscillator should maintain an oven temperature of50° C.
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-8If a spectrum analyzer is not available, connect a digital voltmeter (DVM) to TP1 on thex8 multiplier board. Tune capacitors C6 and C18 for maximum voltage and then alsotune L2 and L4 for maximum voltage output at TP1.Connect the sample output of the channel oscillator, J2 to a suitable counter and tuneC11, coarse adjust, and C9, fine adjust, to the crystal frequency. Note: Do not re-peak C6, C18, L2, or L4 because this may change the outputlevel.Note: While adjusting C9 and C11 to the crystal frequency, the peak voltagemonitored at TP1 of the x8 multiplier board should not decrease. If a decreasedoes occur, there may be a problem with the crystal. Contact ADC Field Supportfor further instructions.Note: If the VCXO board (1145-1204) in the VCXO assembly (1145-1206) isused, C9, the fine-frequency adjust, is not located on the VCXO board, but onthe FSK identifier board by using R18.Reconnect the main output, J1, of the channel oscillator to the input, J1, of the x8multiplier board.4.1.10 (A15-A1) x8 Multiplier Board (1227-1002; Appendix B)This board is mounted in a x8 multiplier enclosure assembly (1227-1240).During normal operation, the green LED DS1, which can be seen through the accesshole in the enclosure assembly, will be lit to indicate that the LO is present at the outputof the x8 multiplier board.To align this board, connect a spectrum analyzer to the output jack, J2, of the board.Tune C4, C6, C10, C12, C18, and C20 for maximum output. Readjust all of thecapacitors to minimize the seventh and the ninth harmonics; they should be at least -30dB downwithout affecting the x8 multiplier output.If a spectrum analyzer is not available, a DC voltmeter can be used, but the harmonicfrequencies must be minimized to prevent interference with other channels.While monitoring each test point with a DC voltmeter, maximize each test point bytuning the broadband multipliers in the following sequence:• Monitor TP1 with a DVM and tune C4 for maximum (typically 0.6 VDC)• Monitor TP2 and tune C6 and C10 for maximum (typically 1.2 VDC)• Monitor TP3 and tune C12 and C18 for maximum (typically 2.0 VDC)• Monitor TP4 and tune C20 for maximum• Re-peak C12 and C10 while monitoring TP4 (typically 3.5 VDC)• The typical output level is +15 dBm.4.1.11 (A19-A1) Visual/Aural Metering Board (1227-1202; Appendix B)This board is mounted in a visual/aural metering enclosure assembly (1227-1212).
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-9The board is adjusted to give a peak-detected output indication to the front panel meterfor combined output, visual-only output, aural-only output, and reflected output. Theboard should need no adjustments to achieve normal operation.4.1.12 (A3-A2) +12-VDC(4A)/-12-VDC(1A) Power Supply Board (1227-1203;Appendix B)This board is mounted in (A3) the +12V(4A)/-12V(1A) power supply assembly (1227-1210).The board has no adjustments.DS1 will be lit if a +12-VDC output is connected to J2. DS2 will be lit if a +12-VDCoutput is connected to J3. DS3 will be lit if a +12-VDC output is connected to J4. DS4will be lit if a +12-VDC output is connected to J5. DS5 will be lit if a –12-VDC output isconnected to J6.4.2 (A1, A2, A3, A4, A5, and A6) 600-Watt UHF Amplifier Trays (1227-1300;Appendix A)The trays have been adjusted at the factory to meet all specifications, including phaseadjustment with other 600-watt amplifier trays, and should not need to be adjusted toattain normal operation. During adjustments of the amplifier boards, switch S1 on theamplifier control board should be in the Manual Gain position. The output voltage from(A12) the switching power supply should be adjusted for +29.5 VDC.4.2.1 (A1) UHF Filter (1007-1101; Appendix B)Apply a multiburst test signal to the transmitter. Monitor J2 with a spectrum analyzerand tune C1 and C3 for peak output with a flat-frequency response.4.2.2 (A2-A1) Variable Gain/Phase Board (1227-1330; Appendix B)This board is mounted in the variable gain/phase enclosure (1227-1331).There are no adjustments to this board; it has an adjustable gain of 0 to 20 dB.4.2.3 (A3-A1) 1-WatT UHF Amplifier Board (1227-1303; Appendix B)This board is mounted in the 1-watt amplifier enclosure (1227-1319).The board has approximately 10 dB of gain and has no adjustments.4.2.4 (A4-A1) Dual Stage Amplifier Board, Class A (1227-1305; Appendix B)This board is part of the dual stage amplifier assembly, class A (1227-1340). The boardoperates class A and has a gain of approximately 11 dB.The biases of the transistors are set by the on-board biasing circuits. Adjust R106 andR206 for 3 amps of idle current, no RF drive applied. Connect a voltage meter across E1and E2 on the amplifier protection board. Move switch S1 to the I2 position and adjustR106 for a reading of 30 mV. Move switch S1 to the I1 position and adjust R206 for areading of 30 mV.
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-10Connect a sweep test signal to J1, the RF input jack of the 600-watt amplifier tray andmonitor the output of the board at J2 with a padded-input spectrum analyzer. Tunecapacitors C104 and C204 for peak output and then tune C106 and C206 for peakoutput power with a flat-frequency response at J2.4.2.5 (A4-A2) Coupler Board Assembly (1227-1316; Appendix B)There are no adjustments to this board.4.2.6 (A4-A3) Dual Stage Amplifier Board, Class AB (1227-1301; Appendix B)This board is part of the dual stage amplifier assembly, class AB (1227-1339).This board operates class AB and has a gain of approximately 9 dB. The biases of thetransistors are set by the on-board biasing circuits. Adjust R106 and R206 for 100milliamps of idle current per side, no RF drive applied. Connect a voltage meter acrossE1 and E2 on the amplifier protection board. Move switch S1 to the I4 position andadjust R106 for a reading of 1.0 mV. Move switch S1 to the I3 position and adjust R206for a reading of 1.0 mV.Connect a sweep test signal to J1, the RF input jack of the 600-watt amplifier tray, andmonitor the output of the board at J2 with a padded-input spectrum analyzer. Tunecapacitors C104 and C204 for peak output and then tune C106 and C206 for peakoutput with a flat-frequency response and minimum current at J2.4.2.7 (A5-A1) 4-Way Splitter Board (1227-1312; Appendix B)There are no adjustments to this board.Monitor the output of the tray at J2 with a padded-input spectrum analyzer.4.2.8 (A5-A2, A5-A3, A5-A4, and A5-A5) Dual Stage Amplifier Boards, Class AB (1227-1301; Appendix B)Each of these boards is part of a dual stage amplifier assembly, class AB (1227-1339).These boards operate class AB and have a gain of approximately 9 dB. The idlingcurrents for each of the transistors are set to 250 mA.To adjust the idling currents, no RF applied to the tray, of the devices on the (A5-A2)amplifier board, connect a voltage meter across E1 and E2 on the amplifier protectionboard and switch S1 to the I6 position. Adjust R106 for a reading of 2.5 mV. Moveswitch S1 to the I5 position and adjust R206 for a reading of 2.5 mV.Connect a sweep test signal to J1, the RF input jack of the 600-watt amplifier tray. Onthe (A5-A2) amplifier board, tune capacitors C104 and C204 for peak output power.Tune C106 and C206 for peak output power with a flat-frequency response andminimum current.To adjust the idling currents, no RF applied to the tray, of the devices on the (A5-A3)amplifier board, connect a voltage meter across E1 and E2 on the amplifier protectionboard. Move switch S1 to the I8 position and adjust R106 for a reading of 2.5 mV. Moveswitch S1 to the I7 position and adjust R206 for a reading of 2.5 mV.Connect a sweep test signal to J1, the RF input jack of the 600-watt amplifier tray. On
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-11the (A5-A3) amplifier board, tune capacitors C104 and C204 for peak output power.Tune C106 and C206 for peak output power with a flat-frequency response andminimum current.To adjust the idling currents, no RF applied to the tray, of the devices on the (A5-A4)amplifier board, connect a voltage meter across E1 and E2 on the amplifier protectionboard. Move switch S1 to the I10 position and adjust R106 for a reading of 2.5 mV.Move switch S1 to the I9 position and adjust R206 for a reading of 2.5 mV.Connect a sweep test signal to J1, the RF input jack of the 600-watt amplifier tray. Onthe (A5-A4) amplifier board, tune capacitors C104 and C204 for peak output power.Tune C106 and C206 for peak output power with a flat-frequency response andminimum current.To adjust the idling currents, no RF applied to the tray, of the devices on the (A5-A5)amplifier board, connect a voltage meter across E1 and E2 on the amplifier protectionboard. Move switch S1 to the I12 position and adjust R106 for a reading of 2.5 mV.Move switch S1 to the I11 position and adjust R206 for a reading of 2.5 mV.Connect a sweep test signal to J1, the RF input jack of the 600-watt amplifier tray. Onthe (A5-A5) amplifier board, tune capacitors C104 and C204 for peak output power.Tune C106 and C206 for peak output power with a flat-frequency response andminimum current.4.2.9 (A5-A6) 4-Way Combiner Board (1227-1311; Appendix B)There are no adjustments to this board.4.2.10 (A5-A7) CirculatorThe circulator contains no adjustments.4.2.11 (A6-A1) Dual Peak Detector Board, Single Supply (1227-1333; AppendixB)There are no adjustments to this board.4.2.12 (A7) Amplifier Protection Board (1227-1306; Appendix B)There are no adjustments to this board. One of the red LEDs, DS1 to DS13, will light ifthe fuse associated with it is opened.4.2.13 (A8) Amplifier Control Board (1227-1308; Appendix B)To check the operation of the overdrive circuit, increase the gain pot of the 600-wattamplifier tray to approximately 110%. The Overdrive LED DS2 should light and theoutput power should not increase above the 110% level.4.2.14 Calibration of Output Power and VSWR CutbackTo calibrate the output power and VSWR cutback of the 600-watt amplifier trays, place awattmeter and dummy load of at least 600 watts at the output of the tray that is to becalibrated and switch the front panel meter to the % Output Power position. Preset R16,manual gain, on (A8) the amplifier control board (1227-1308) fully CCW.
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-12Move switch S1 on the amplifier control board to the Manual position. Insert a visual-only with sync-only test signal to the system and verify 40 IRE units of sync. Adjust R16for 360 watts on the wattmeter. Monitor a sample of the output with a spectrumanalyzer set to the zero-span position and adjust the spectrum analyzer so that thelevel of the output is at the top line of the gaticule. Insert -13 dB of aural to the visualsync-only test signal and adjust R16 for the same visual-only input reference level onthe spectrum analyzer. The output power on the wattmeter should be approximately450-watts visual +/-13-dB aural. Calibrate the front panel output power meter to 100%with R2, forward calibration, on the amplifier control board.Reduce manual gain pot R16 to a 50% reading on the front panel meter in the %Output Power position. Turn the tray off. Remove the load from the output of the trayand switch the front panel meter to the Reflected Output Power position. Switch the trayon. Adjust reflected power adjust pot R22, on the amplifier control board, for a 50%reading. Then adjust R29, the VSWR threshold cutback pot on the amplifier controlboard, until the VSWR Cutback LED DS1 on the front panel just lights. This sets up theVSWR cutback circuitry.After the setup is completed, move switch S1 on the amplifier control board to theAutomatic Gain Control position; this is the normal operating position for the switch. This completes the alignment procedures for the 600-watt UHF amplifier tray. The trayis now aligned, calibrated, and ready for normal operation.4.3 Alignment of (A9) the Bandpass Filter and (A10) the Output Trap FilterThe (A9) bandpass filter (A9) and (A10) the output trap filter are tuned to rejectunwanted distortion products generated when the signals are diplexed and also duringthe amplification process. The bandpass filter is factory tuned to the proper bandwidthand should not need to be re-tuned. Please consult the ADC Field Support Departmentbefore tuning the filters.The traps on the output trap filter are labeled with their center frequency relative to thefrequency of the carrier (for example, the traps labeled -4.5 MHz are tuned for a centerfrequency of 4.5 MHz lower than the frequency of the visual carrier).The trap sections are reflective notches that can be adjusted across the entire UHFfrequency band. The electrical length of the outer sleeve and the center rod of the notchcan be adjusted to tune the notch frequency. The depth of the notch is set by the gapbetween the center conductor of the trap section and the center conductor of the mainline. Tight coupling makes a deep notch, while loose coupling makes a shallow notch.The trap sections have been factory tuned and should not need major adjustments. Thefrequency, relative to the visual carrier, that the trap is tuned to is marked on that trapsection. Fine tuning of the center frequency of the notches can be accomplished with the tuningbolts on the side of the filter section. Loosen the nut locking the bolt in place and adjustthe bolt to change the frequency of the notch. Monitor the output of the transmitterwith a spectrum analyzer and null the distortion product with the bolt. Red field is agood video test signal to use to see the +8.08-MHz product. Tighten the nut when thetuning is completed. Hold the bolt in place with a screwdriver as the nut is tightened toprevent it from slipping.
3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures835-3, Rev. 0 4-13For major tuning, such as changing the notch depth or moving the notch frequencymore than 1 MHz, the outer conductor and the center conductor of the trap section mustboth be moved. This requires an RF sweep generator to accomplish. Apply the sweepsignal to the input of the trap filter and monitor the output. Loosen the clamp holdingthe outer conductor in place and make the length longer to lower the frequency of thenotch or shorter to raise the frequency of the notch. Loosen the center conductor withan Allen wrench and move it deeper for a lower-frequency notch or out for a higher-frequency notch. These adjustments must both be made in order to change the notch frequency; theeffects of these adjustments are shown in Table 4-1. Moving only the center conductoror the outer conductor will effect the notch depth in addition to the center frequency.The variable that is being adjusted with this procedure is the length of the centerconductor inside the trap filter. The gap between the trap and the main line should notbe changed. Moving only the inner or the outer conductors by themselves will affectboth the gap and the notch depth.To effect the notch depth only, both sections will have to be moved. The notch depth iscontrolled by the gap between the center conductor and the trap section. This gap alsohas an effect on the center frequency. To deepen the notch, shorten the outer conductorand pull the center conductor out until the notch is back in the same place. Move thesections in the opposite direction to make a shallow notch.Table 4-1. Effects of Tuning the Output Trap FilterADJUSTMENT EFFECTLengthening 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 tuning has been completed, tighten the clamp and the Allen screws that hold theconductors. Use the fine-tuning bolts to bring in the frequency. The final tuningadjustments should be completed with the transmitter driving the output trap filter forat least one hour to allow for drift during the warming-up period.This completes the alignment procedures for the bandpass filter and output trap filterassembly.

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