OUS840A10,000-watt UHF solid state television transmitter

ADC-840A Type Acceptance Report Users Manual July 20005-1 5. USER’S MANUAL The user’s manual for the ADC-840A system is provided as separate files to this type acceptance report.

10-kW UHF Transmitter with Chapter 1, Introduction Feedforward Drive 840A, Rev. 01-1 Chapter 1 Introduction This manual explains the installation, setup, alignment, and maintenance procedures for the 840A 10-kW UHF transmitter with feedforward drive. It is important that you read all of the instructions, especially the safety information in this chapter, before you begin to install or operate the unit. 1.1 Manual Overview This instruction manual is divided into five chapters and supporting appendices. Chapter 1, Introduction, contains information on the assembly numbering system used in the manual, safety, maintenance, return procedures, and warranties. The second chapter describes the transmitter and includes discussions on system control and status indicators as well as remote control connections. Chapter 3 explains how to unpack, install, setup, and operate the transmitter. Chapter 4 contains a detailed discussion of the circuits and boards that make up the 840A transmitter. Chapter 5, Detailed Alignment Procedures, provides information on adjusting the system to achieve peak operation of the assemblies. The appendices contain assembly and subassembly drawings and parts lists as well as system specifications. 1.2 Assembly Designation Procedure ADC has assigned assembly numbers, such as Ax (x=1,2,3...), to all assemblies, trays, and boards that are referenced in the text of this manual and shown on the block diagrams and interconnect drawings provided in the appendices. These supporting documents are arranged in increasing numerical order in the appendices. Section titles in the text for assembly and tray descriptions or alignment procedures also indicate the associated drawing(s) and the relevant appendix that contains that drawing. Sections describing vendor-supplied items, such as meters and power supplies, do not contain this information. 1.3 Safety The UHF transmitters manufactured by the Broadcast Systems Division of ADC are designed to be easy to use and repair while providing protection from electrical and mechanical hazards. Listed throughout the manual are notes, cautions, and warnings concerning possible safety hazards that may be encountered while operating or servicing the transmitter. Please review these warnings and familiarize yourself with the operation and servicing procedures before working on the transmitter. Read All Instructions – All of the operating and safety instructions should be read and understood before operating this equipment. Retain Manuals – The manuals for the transmitter should be retained at the transmitter site for future reference. We provide two sets of manuals for this purpose; one set can be left at the office while one set can be kept at the site. Heed all Notes, Warnings, and Cautions – All of the notes, warnings, and cautions listed in this safety section and throughout the manual must be followed. Follow Instructions – All of the operating and use instructions for the transmitter should be followed. Cleaning – Unplug or otherwise disconnect all power from the equipment before cleaning. Do not use liquid or aerosol cleaners. Use a damp cloth for cleaning. 10-kW UHF Transmitter with Chapter 1, Introduction Feedforward Drive 840A, Rev. 01-2 Ventilation – Openings in the cabinets and tray front panels are provided for ventilation. To ensure reliable operation of the transmitter, and to protect the unit from overheating, these openings must not be blocked. Servicing – Do not attempt to service this product yourself until becoming familiar with the equipment. If in doubt, refer all servicing questions to qualified ADC service personnel. Replacement Parts – When replacement parts are used, be sure that the parts have the same functional and performance characteristics as the original part. Unauthorized substitutions may result in fire, electric shock, or other hazards. Please contact the ADC Technical Service Department if you have any questions regarding service or replacement parts. 1.4 Maintenance The 840A is designed with components that require little or no periodic maintenance except for the routine cleaning of the fans and the front panels of the trays. The amount of time between cleanings depends on the conditions within the transmitter room. While the electronics have been designed to function even if covered with dust, a heavy buildup of dust, dirt, or insects will affect the cooling of the components. This could lead to a thermal shutdown or premature failure of the affected trays. When the front panels of the trays become dust covered, the top covers should be removed and any accumulated foreign material should be removed. A vacuum cleaner, utilizing a small wand- type attachment, is an excellent way to suction out the dirt. Alcohol and other cleaning agents should not be used unless you are certain that the solvents will not damage components or the silk- screened markings on the trays and boards. Water-based cleaners can be used, but do not saturate the components. The fans and heatsinks should be cleaned of all dust or dirt to permit the free flow of air for cooling purposes. It is recommended that the operating parameters of the transmitter be recorded from the meters on the trays and the system metering control panel at least once a month. It is suggested that this data be retained in a rugged folder or envelope. 1.5 Material Return Procedure To insure the efficient handling of equipment or components that have been returned for repair, ADC requests that each returned item be accompanied by a Material Return Authorization Number (MRA#). An MRA# can be obtained from any ADC Field Service Engineer by contacting the ADC Field Service Department, Broadcast Systems Division, at (724) 941-1500 or by fax at (724) 941-4603. This procedure applies to all items sent to the Field Service Department regardless of whether the item was originally manufactured by ADC. Note: To prevent damage to the product during shipping, ADC supplies a shippin…

Text truncated - open the document above for the full version.

10-kW UHF Transmitter with Chapter 2, System Description Feedforward Driver 840A, Rev. 02-1 Chapter 2 System Description The 840A (1064941) is a complete 10- kW UHF internally diplexed television transmitter that operates at a nominal visual output power of 10,000 watts peak sync visual and an average aural output power of 1000 watts with a 10 dB aural/visual ratio. 2.1 System Overview The 840A is made up of three cabinet assemblies: the (A1) dual 250-watt driver/amplifier assembly (1064946); (A2) the 10-kW amplifier assembly (1299-1100); and (A3) the high-voltage power supply assembly, 208/240 VAC (1068022). 2.1.1 (A1) Dual 250-Watt Exciter/Amplifier Assembly (1064946; Appendix A) The dual 250-watt driver/amplifier assembly is made up of the assemblies and trays shown in Table 2-1. Table 2-1. Driver/Amplifier Assembly Assemblies and Trays DESIGNATION NUMBERTRAY/ASSEMBLY NAMEDRAWING NUMBER A2AC distribution assembly1265-1600 A4UHF exciter tray1063301 A93-watt amplifier tray1068203 A6 and A7250-watt amplifier trays 1044027, low-band; 1044028, mid-band; 1044029, high-band A14Bandpass filter assembly-- The exciter/amplifier assembly (1064946) is connected to the baseband video and aural inputs. The assembly also provides connections for the remote monitoring and operation of the exciter/amplifier assembly. The UHF exciter tray (1063301) takes the baseband aural and video inputs and produces the visual and aural RF signals on the channel frequencies. The combined visual and aural RF output (+7 dBm) of the exciter feeds the 3-watt amplifier tray (1068203). The 3-watt amplifier tray contains an automatic gain control circuit and two 3-watt amplifier boards. The tray generates the output level needed to drive the 250-watt amplifier trays (1044027, low-band; 1044028, mid-band; and 1044029, high- band). The output from the 3-watt tray is fed to the (A10) RF hybrid splitter SMA connection J1. The RF hybrid splitter output feeds the RF signal to one of the 250-watt amplifiers directly and, through (A5) the line stretcher, to the other 250- watt amplifier. The line stretcher gives the operator the ability to control the phase of the output signal that is fed to one of the 250-watt trays. Each of the 250-watt amplifier trays contains an amplifier enclosure and feedforward circuits to achieve an output of 250-watts peak visual power and 25 watts of aural power. In the 250-watt amplifier tray, a forward power sample from the UHF coupler is connected to the dual peak detector board; this board provides a peak- detected forward sample to the amplifier control board for metering purposes. Before exiting the 250-watt amplifier tray, the RF is fed through a circulator for the protection of the tray from high VSWR conditions. The reject port of the circulator is cabled to the reject 10-kW UHF Transmitter with Chapter 2, System Description Feedforward Driver 840A, Rev. 02-2 load/coupler board; this board supplies the reflected sample to the dual peak detector board, single supply. This signal is then sent to the amplifier control board for metering purposes. The output of the 250-watt visual amplifier trays is combined in a UHF tee combiner, and fed through (A14) a bandpass filter and (A11) a directional coupler, before being connected with1/2" heliax to the RF input jack (A2-A1-J1) of the tube cavity assembly in the 10-kW amplifier assembly cabinet. The combined output of the 250-watt visual amplifier trays (350 watts) is the level needed to drive the 10-kW amplifier to 10,000 watts peak sync visual output. The main AC input to the exciter/amplifier assembly is (A2) the AC distribution panel assembly (1265-1600). The AC distribution panel assembly contains a terminal block (TB1) that connects to the main AC input (208/240 VAC). The terminal block has four metal- oxide varistors (MOVs) connected across the input lines for surge and transient protection. The AC distribution panel contains CB1, the 40-amp main AC circuit breaker that distributes the AC through the circuit breakers CB2 to CB7 to the exciter and amplifier trays. 2.1.2 (A2) 10-kW Diacrode Amplifier (1299-1100; Appendix A) The (A11) metering control panel (1293- 1308) on the amplifier assembly provides the operator with front panel metering for all voltage (M1 using S1) and current (M2 using S3) readings that apply to the tube. The metering control panel also provides the aural, visual, and reflected output power readings for the transmitter using meter M3 with switch S4. The front panel assembly contains the switches that control the Operate/Standby (S5) and Automatic/Manual (S6) operation of the 10-kW amplifier. When switched to Operate, the panel supplies the driver enable (Operate command) to the exciter/amplifier assembly. The Automatic/Manual switch selects either the automatic operation of the transmitter, which uses the video input to control the on/off state of the transmitter, or the Normal front panel control, manual operation, of the transmitter. The metering control panel also provides front panel control, through switch S8, of the Visual Output Power level. High-Voltage Enable/Disable switch S7 controls the high-voltage power supply from the front panel of the 10-kW diacrode amplifier. Normal/Exciter Test switch S10, when in the Exciter Test position, gives the operator the ability to operate the exciter/amplifier assembly without operating the 10-kW amplifier. Note: The exciter/amplifier assembly output must be terminated into a dummy load prior to using this function . The metering control panel also has LEDs on the front panel for a visual indication of the operating status of the transmitter: Operate/Standby, Auto/Manual, High Voltage Enable/Disable, Driver Mode Normal/Test, 3-Fault with Fault Reset Switch (S9), Fault Status Overtemp, and VSWR Cutback. The front panel has command status LEDs that indicate, when they are lit, that the command has been given. In addition, the front panel has Operate status LEDs that indicate, when t…

Text truncated - open the document above for the full version.

10-kW UHF Transmitter with Chapter 3, Installation and Feedforward Drive Setup Procedures 840A, Rev. 03-1 Chapter 3 Installation and Setup Procedures There are special considerations that need to be taken into account before the 840A can be installed. For example, if the installation is completed during cool weather, a heat-related problem may not surface for many months, suddenly appearing during the heat of summer. This section provides planning information for the installation and set up of the transmitter. 3.1 Site Considerations The 840A transmitter requires two main AC input lines, a 3-phase 208/240 VAC, 60 Hz input of at least 100 amp rating that connects to the high-voltage power supply assembly and a single-phase 208/240 VAC, 60 Hz input of at least 40 amp rating that connects to the exciter/driver assembly. Make sure that the proposed site has the necessary voltage requirements. The cabinets should be positioned with consideration given for adequate air intake and exhaust. In addition, installation planning should take into account the amount of space required for the opening of the front of the metering control panel on the 10-kW amplifier; the opening of the rear doors on the 10-kW amplifier and exciter/driver cabinets; access to the trays, including sliding them out for testing; the main AC hook- up to the high-voltage power supply assembly; and the installation of the output transmission line, including the trap filters and the directional coupler. The 10-kW amplifier cabinet contains a tube cavity air exhaust stack that is a 10.5-inch chimney mounted on the roof of the cabinet. Forced air flows though this chimney from the blower assembly that cools the tube mounted in the cavity assembly (1,100 CFM at 30° C rise). The 10-kW amplifier cabinet also has two exhaust fans, rated at 240 CFM, mounted in the top cover assembly of the cabinet. Air intake for the tube cavity blower assembly is through the large filter mounted on the bottom rear of the cabinet. The high-voltage power supply cabinet has two exhaust fans, each rated at 550 CFM, mounted in the top cover assembly of the cabinet. Air intake for the cabinet is through the two filters mounted on each side of the cabinet. The 840A is designed and built to provide long life with a minimum of maintenance. The environment in which it is placed is important and certain precautions must be taken. The three greatest dangers to the transmitter are heat, dirt, and moisture. Heat is usually the greatest problem, followed by dirt, and then moisture. Over-temperature can cause heat-related problems such as thermal runaway and component failure. Each amplifier tray in the transmitter contains a thermal interlock protection circuit that will shut down that tray until the temperature drops to an acceptable level. A suitable environment for the transmitter can enhance the overall performance and reliability of the transmitter and maximize revenues by minimizing down time. A properly designed facility will have an adequate supply of cool, clean air, free of airborne particulates of any kind, and no excessive humidity. An ideal environment will require temperature in the range of 40° F to 70° F throughout the year, reasonably low humidity, and a dust-free room. It should be noted that this is rarely if ever attainable in the real world. However, the closer the environment is to this design, the greater the operating capacity of the transmitter. 10-kW UHF Transmitter with Chapter 3, Installation and Feedforward Drive Setup Procedures 840A, Rev. 03-2 The fans and blowers designed and built into the transmitter will remove the heat from within the trays, but additional means are required for removing this heat from the building. To achieve this, a few considerations should be taken into account. The first step is to determine the amount of heat to be removed. There are generally three sources of heat that must be considered. The first and most obvious is the heat from the transmitter itself. This can be determined by subtracting the average power to the antenna (6950 watts) from the AC input power (25,000 watts). This number in watts (18,050) is then multiplied by 3.41, which gives 61,550, the BTUs to be removed every hour. 12,000 BTUs per hour equals one ton, so a 6-ton air conditioner will cool a 10-kW transmitter that is vented into the room. If the air exhaust will be vented externally, a 1.5- ton air conditioner will be needed to properly cool the transmitter. The second source of heat is other equipment in the same room. This number is calculated in the same way as the equation for BTUs. The third source of heat is equally obvious but not as simple to calculate. This is the heat coming through the walls, roof, and windows on a hot summer day. Unless the underside is exposed, the floor is usually not a problem. Determining this number is usually best left up to a qualified HVAC technician. There are far too many variables to even estimate this number without detailed drawings of the site showing all construction details. The sum of these three sources is the total amount of heat that must be removed. There may be other sources of heat, such as personnel, and all should be taken into account. Now that the amount of heat that must be removed is known, the next step is to determine how to accomplish this. The options are air conditioning, ventilation, or a combination of the two. Air conditioning is always the preferred method and is the only way to create anything close to an ideal environment. Ventilation will work if the ambient air temperature is below 100° F, or about 38° C, and the humidity is be kept at a reasonable level. In addition, the air stream must be adequately filtered to ensure that no airborne particulates of any kind will be carried into the transmitter. The combination of air conditioning for summer and ventilation during the cooler months is acceptable when the proper cooling cannot be obtained through the use of ventila…

Text truncated - open the document above for the full version.

10-kW UHF Transmitter with Chapter 4, Circuit Feedforward Drive Descriptions 840A, Rev. 04-1 Chapter 4 Circuit Descriptions 4.1. (A1) Dual 250-Watt Driver/Amplifier Assembly (1094334; Appendix A) 4.1.1 (A1-A4) UHF Exciter Tray (1094019; Appendix A) 4.1.1.1 (A4) Aural IF Synthesizer Board, 4.5 MHz (1265-1303; Appendix B) The aural IF synthesizer board amplifies each of the three possible audio inputs and the amplifier circuits that supply the single audio output. The balanced audio or the composite audio input is connected to the board while the subcarrier audio (SCA) input can be connected at the same time as either of the other two inputs. The board has the 4.5-MHz voltage-controlled oscillator (VCO) and the aural modulation circuitry that produces the modulated 4.5-MHz output. The board also contains a phase lock loop (PLL) circuit that maintains the precise 4.5-MHz separation between the aural (41.25 MHz) and the visual (45.75 MHz) IF frequencies. Balanced Audio Input The first of the three possible baseband inputs to the board is a 600Ω-balanced audio input (+10 dBm) that enters through jack J2, pins 1 (+), 2 (GND), and 3 (-), and is buffered by U1B and U1C. Diodes CR1 to CR4 protect the input stages of U1B and U1C if an excessive signal level is present on the input leads of jack J2. The outputs of U1B and U1C are applied to differential amplifier U1A; U1A eliminates the common mode signals (hum) on its input leads. A pre-emphasis of 75 ms is provided by R11, C11, and R10 and can be eliminated by removing jumper W5 on J5. The signal is then applied to amplifier U1D whose gain is controlled by jumper W3 on J11. Jumper W3 on jack J11 is positioned according to the input level of the audio signal (0 or +10 dBm). If the input level is approximately 0 dBm, the mini-jumper should be in the high gain position between pins 1 and 2 of jack J11. If the input level is approximately +10 dBm, the mini-jumper should be in low gain position between pins 2 and 3 of jack J11. The balanced audio is then connected to buffer amplifier U2A whose input level is determined by the setting of balanced audio gain pot R13. The output of the amplifier stage is wired to the summing point at U2D, pin 13. Composite Audio Input The second possible audio input to the board is the composite audio (stereo) input at BNC jacks J3 and J13. The two jacks are loop-through connected; as a result, the audio can be used in another application by connecting the unused jack and removing W4 from J12. Jumper W4 on jack J12 provides a 75Ω-input impedance when the jumper is between pins 1 and 2 of jack J12 and a high impedance when it is between pins 2 and 3. Diodes CR9 to CR12 protect the input stages of U6A and U6B if an excessive signal level is applied to the board. The outputs of U6A and U6B are applied to differential amplifier U2C, which eliminates common mode signals (hum) on its input leads. The composite input signal is then applied to amplifier U2B; the gain of this amplifier is controlled by composite audio gain pot R17. The composite audio signal is connected to the summing point at U2D, pin 13. Subcarrier Audio Input The third possible input to the board is the SCA input at BNC jack J4. The SCA input has an input impedance of 75Ω that can be eliminated by removing jumper W2 from pins 1 and 2 of J14. The SCA input is bandpass filtered by C66, C14, R22, C15, C67, and R23 and is fed to 10-kW UHF Transmitter with Chapter 4, Circuit Feedforward Drive Descriptions 840A, Rev. 04-2 buffer amplifier U3A. The amplified signal is then applied though SCA gain pot R24 to the summing point at pin 13 of U2D. Audio Modulation of the VCO The balanced audio, or the composite audio and/or the SCA-buffered audio signals, are fed to the common junction of resistors R14, R20, and R27 that connect to pin 13 of amplifier U2D. The output audio signal at pin 14 of U2D is typically .8 Vpk-pk at a ±25-kHz deviation for balanced or .8 Vpk-pk at ±75-kHz deviation for composite as measured at TP1. This signal is applied to VCO U10. A sample of the deviation level is amplified, detected by U7A and U7B, and connected to J10 on the board. This audio-deviation level is connected to the front panel meter through the transmitter control board. The audio is connected to CR13 to CR16; these are varactor diodes that frequency modulate the audio signal onto the generated 4.5-MHz signal in U10. U10 is the 4.5-MHz VCO that generates the 4.5- MHz continuous wave (CW) signal. The output frequency of this signal is maintained and controlled by the correction voltage output of U5 PLL IC. The audio-modulated, 4.5-MHz signal is fed to amplifiers U11A and U11B. The output of U11B is connected to the 4.5- MHz output jacks at J7 and J8. Phase Lock Loop (PLL) Circuit A sample of the signal from the 4.5-MHz aural VCO at the output of U11A is applied to PLL IC U5 at the F in connection. In U5, the signal is divided down to 50 kHz and is compared to a 50- kHz reference signal. The reference signal is a divided-down sample of the visual IF, 45.75-MHz signal that is applied to the oscillator-in connection on the PLL chip through jack J6 on the board. These two 50-kHz signals are compared in the IC and the fV, and fR is applied to the differential amplifier U3B. The output of U3B is fed back through CR17 to the 4.5-MHz VCO IC U10; this sets up a PLL circuit. The 4.5-MHz VCO will maintain the extremely accurate 4.5- MHz separation between the visual and aural IF signals; any change in frequency will be corrected by the AFC error voltage. PLL chip U5 also contains an internal lock detector that indicates the status of the PLL circuit. When U5 is in a "locked" state, pin 28 goes high and causes the green LED DS1 to illuminate. If the 4.5- MHz VCO and the 45.75-MHz oscillator become "unlocked," out of the capture range of the PLL circuit, pin 28 of U5 will go to a logic low and cause the red LED DS2 to light. A mute output signal from Q3 (unlock mute) will be applied to jack J9.…

Text truncated - open the document above for the full version.

10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures Feedforward Drive 840A, Rev. 0 5-1 Chapter 5 Detailed Alignment Procedures This transmitter was aligned at the factory and should not require additional alignments to achieve normal operation. Before beginning the alignment procedures, check that the RF output at J2 of (A18) the output coupler assembly of the transmitter is terminated into a dummy load or is connected to the antenna. While performing any alignments, refer to the Test Data Sheet for the transmitter and compare the final readings from the factory with the readings on each of the trays. They should be very similar. If a reading is off by a substantial amount, the problem is likely to be in that tray. 5.1 (A1-A4) UHF Exciter Tray (1063301; Appendix A) If the (optional) 4.5-MHz composite input kit has been purchased, the UHF exciter tray is capable of operating using either the 4.5-MHz composite input or the baseband audio and video inputs. The kit adds (A24) the composite 4.5-MHz filter board and (A25) the 4.5-MHz bandpass filter board to the UHF exciter. The 4.5 MHz generated by the aural IF synthesizer board is not used when the 4.5-MHz composite input kit has selected the 4.5-MHz intercarrier signal generated by the 4.5-MHz composite input. The composite 4.5-MHz filter board and the 4.5-MHz bandpass filter board are not used when the 4.5-MHz composite input kit uses the 4.5-MHz intercarrier signal generated by the baseband video and audio inputs with baseband select. The exciter tray has been factory tuned and should not need to be aligned to achieve normal operation. To align the UHF exciter for 4.5-MHz composite input, apply the 4.5-MHz composite input, with the test signals used as needed, to video input jack J1 on the rear of the tray. Select the 4.5-MHz composite input by removing the baseband select from J7-6 and J7-7 on the rear of the tray, if applied. To align the UHF exciter using baseband video and audio inputs, connect the baseband video, with the test signals used as needed, to video input jack J2 on the remote interface panel. For balanced audio input, connect the baseband audio to TB1-1(+), TB1-2(-), and TB1-3 (GND) on the remote interface panel. For composite/stereo audio, connect the stereo source to J6 on the remote interface panel. 5.1.1 (A6) (Optional) Delay Equalizer Board (1227-1204; Appendix B) This board has been factory tuned and should not be retuned without the proper equipment. If it is necessary to tune the board: 1. Select a sinX/X test signal as the video source to the delay equalizer board. 2. Monitor the video output of the board at video sample jack J2 with a video measuring set (VM700) that has been adjusted to measure group delay. 3. Tune the four stages of the board using the variable inductors (L1-L4) and potentiometers (R7, R12, R17, and R22) until the signal attains the FCC group delay curve. The stages are arranged in order of increasing frequency. Adjust R29 as needed to attain the same level coming out of the board as is going into the board. 10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures Feedforward Drive 840A, Rev. 0 5-2 5.1.2 (A24) (Optional) Composite 4.5-MHz Filter Board (1227-1244; Appendix B) The (A24) (optional) composite 4.5-MHz filter board will only function properly with a 4.5-MHz composite input signal and with the 4.5-MHz composite input selected. Connect the test signal from an envelope delay measurement set to the video input of the tray at J1 or J2. Connect an oscilloscope to jack J7, video out, between the J7 center pin and pin 1 or 3 ground. Adjust C21, frequency response, if needed, for the best frequency response. Adjust R32, video gain, for a signal level of 1 Vpk-pk on the oscilloscope. The output at J6 and J7 of the board should be video only with no 4.5-MHz aural subcarrier. 5.1.3 (A25) (Optional) 4.5-MHz Bandpass Filter Board (1265-1307; Appendix B) The (A25) (optional) 4.5-MHz bandpass filter board will only function properly with a 4.5-MHz composite input signal and with the 4.5-MHz composite input selected. Adjust the filter with L2, C3, L4, and C7 for a frequency response of no greater than ±.3 dB from 4.4 to 4.6 MHz. Adjust C19 for an overall peak-to-peak variation of less than ±.3 dB from 4.4 MHz to 4.6 MHz. Recheck the frequency response; it may have changed with the adjustment of the envelope delay. If necessary, retune the board. 5.1.4 (A7) IF Carrier Oscillator Board (1191-1404; Appendix B) To align (A7) the IF carrier oscillator board: 1.While monitoring J3 with a spectrum analyzer, observe the 45.75-MHz visual IF (typical +5 dBm). 2.Connect a frequency counter to J3 and adjust C17 for 45.750000 MHz. 3.Connect a frequency counter to J1 and check for 50 kHz; this is the aural 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 J3 is present. Jumper W4 terminates the video input into 75Ω. Remove jumper W4 if the video loop- through is required on the rear chassis at jacks J1 and J2. 2.Set the controls R20, the white clip, R24, the sync clip, and R45, the sync stretch cut-in, to their fully counter-clockwise (CCW) position. Set R48, the sync magnitude, fully clockwise (CW). 3.Place the jumper W7 on jack J4 to the clamp off, disable, position. 4.Connect a 5-step staircase video test signal to the input of the transmitter. 5.Monitor TP2 with an oscilloscope. Adjust R12, the video gain pot, for 1 Vpk-pk. 6.Change the video input test signal to a multiburst test pattern. While 10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures Feedforward Drive 840A, Rev. 0 5-3 monitoring TP2, adjust C8 and R32 for a flat-frequency response. Change the input …

Text truncated - open the document above for the full version.