INSTRUCTION MANUAL DT835A DIGITAL UHF TRANSMITTER AXCERA, LLC 103 FREEDOM DRIVE P.O. BOX 525 LAWRENCE, PA 15055-0525 USA (724) 873-8100 • FAX (724) 873-8105 www.axcera.com • info@axcera.
Digital UHF Transmitter Table of Contents TABLE OF CONTENTS CHAPTER 1 INTRODUCTION Section 1.1 1.2 1.3 1.4 1.5 Page Manual Overview ..................................................................................1-1 Safety .................................................................................................1-1 Maintenance ........................................................................................1-2 Material Return Procedure ....................................................
Digital UHF Transmitter Table of Contents TABLE OF CONTENTS CHAPTER 4 CIRCUIT DESCRIPTIONS - Continued Section Page 4.3.4 PLL Board ...................................................................................4-5 4.3.5 Power Entry Module.....................................................................4-7 4.3.6 IF Phase Corrector Board .............................................................4-7 4.3.7 ALC Board ..................................................................................
Digital UHF Transmitter Table of Contents TABLE OF CONTENTS - (continued) Section Page CHAPTER 5 DETAILED ALIGNMENT PROCEDURES 5.1 DM8-R Modulator ..................................................................................5-1 5.1.1 DM8-R Modulator Board Configuration .........................................5-1 5.2 UHF Exciter Tray ...................................................................................5-2 5.2.1 Delay Equalization Adjustment.............................................
Digital UHF Transmitter Table of Contents LIST OF FIGURES 2-1 2-2 Exciter Remote Interface Assembly ................................................ 2-10 Amplifier Array Remote Interface Panel .......................................... 2-14 3-1 3-2 1 kW Minimum Ventilation Configuration...........................................3-4 Tray Installation Instructions ...........................................................3-6 5-1 Typical Digital Spectrum ................................................
Digital UHF Transmitter Table of Contents LIST OF TABLES 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14 DT835A Major Assemblies ...............................................................2-1 Metering Panel Meters.....................................................................2-4 UHF Exciter Tray Meters..................................................................2-5 UHF Exciter Tray Switches...............................................................
Digital UHF Transmitter Chapter 1, Introduction Chapter 1 Introduction This manual explains the installation, setup, alignment, and maintenance procedures for the DT835A Digital UHF Transmitter. 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. procedures before working on the transmitter.
Digital UHF Transmitter Chapter 1, Introduction hazards. Please contact the Axcera Technical Service Department if you have any questions regarding service or replacement parts. To insure the efficient handling of equipment or components that have been returned for repair, Axcera requests that each returned item be accompanied by a Material Return Authorization Number (MRA#). 1.
Digital UHF Transmitter Chapter 1, Introduction 1.5 Limited One-Year Warranty for Axcera Products damage (including direct, consequential, or incidental) caused by the breach of any or all warranties, shall be limited to the following: (a) repairing or replacing (in Axcera’s sole discretion) any defective parts free of charge (F.O.B. Axcera’s plant) and/or (b) crediting (in Axcera’s sole discretion) all or a portion of the purchase price to the buyer.
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections Chapter 2 System Description and Customer Remote Connections MAJOR ASSEMBLY NUMBER A1 A2 and A3 A4 A7 TRAY/ASSEMBLY NAME Single UHF exciter assembly two 2-3kW amplifier array assemblies Hybrid combiner assembly Directional coupler assembly Output coupler assembly DM8-R digital modulator tray Table 2-1: DT835A Major Assemblies processed digital IF signal is then cabled to the J32 on the ALC board (12651305).
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections is located in the (Optional) (A10) 10-MHz reference kit (1286-1108). The board contains a high-stability crystal oscillator that provides a 10-MHz output that is used as reference frequency for the transmitter. The board is mounted within an enclosed assembly that helps to maintain the operating temperature of the oscillator board. variable phase/gain tray connects to (A2) the side A amplifier array assembly.
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections A4, A5 & A6) UHF amplifier trays, (A7) a 4 to 6-way combiner, (A8) an output coupler, (A10) an AC distribution assembly, and (A11) an interface panel. combines the output from the amplifier assemblies into a single output. The reject output of the hybrid combiner is connected to (A7) an output coupler that provides a reject sample from J3 to the metering panel in the single UHF exciter assembly for monitoring purposes.
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections On the UHF exciter tray, switch (S1) is an Operate/Standby switch that provides the Operate command (Enable), when in Operate, to the each of the amplifier arrays. The Enable to each amplifier array is split four, five or six ways and then applied to the UHF amplifier trays. The Enable is needed to turn on the switching power supplies located in the UHF amplifier trays.
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections 2.1.8 UHF Exciter Tray METER Meter (A18) Switch (S3), meter ALC (0 - 1 V) % Exciter SWITCH Transmitter (S1) Operate/Standby Mode Select (S2) Auto/Manual FAULT INDICATOR Modulation loss (DS9 red) VSWR cutback (DS7 amber) DT835A, Rev. 1 Table 2-3: UHF Exciter Tray Meters FUNCTION Displays power in terms of a percentage of the calibrated exciter output level on the upper scale.
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections Table 2-6: UHF Exciter Tray Samples DESCRIPTION A sample of the channel oscillator output taken from the sample jack of the PLL board An output power sample of the exciter taken from the UHF upconverter board SAMPLE f(s) Exciter O/P 2.1.
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections Table 2-10: UHF Amplifier Tray Status Indicators INDICATOR FUNCTION Enable (DS4 green) Indicates that an Enable, Operate command, is applied to the UHF amplifier tray from the selected UHF exciter tray Overdrive (DS2 red) Indicates that the level of the drive is too high. The protection circuit will limit the drive to the set threshold. The fault is generated on the amplifier control board.
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections 2.1.12 Main AC Input that only used as part of the 2.5 and 3 kW amplifier array assemblies. The transmitter needs an AC input of 208/240 VAC at 100 amps for each amplifier array assembly and at 20 amps for the exciter assembly. The 208/240 VAC input to the single UHF exciter assembly connects to (A8) the AC distribution assembly, single UHF exciter assembly (1245-1500), in the right, center rear of the cabinet.
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections Figure 2-1: Exciter Remote Interface Assembly Jack (J7) should have a dummy plug connected to it, with a jumper connected between pins 1 and 2, to provide the interlock to the exciter needed to operate the transmitter. If the jumper is missing, the transmitter will not switch to Operate. If remote connections are made to the transmitter, they should be made DT835A, Rev.
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections Table 2-14: Remote Control Interface Connections REMOTE JACK/PIN FUNCTION INTERFACE TYPE NUMBER Exciter Enable Interlock Exciter Enable Interlock Rtn J7-1 J7-2 J7-1 and 2 must be jumpered together for normal operation.
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections REMOTE JACK/PIN NUMBER INTERFACE TYPE Exciter VSWR Cutback Indicator J8-7 50 mA max current sink Video Loss Indicator Video Loss Indicator Rtn J9-7 J9-8 50 mA max current sink Exc Receiver Fault Ind (optional) J8-9 50 mA max current sink FUNCTION Side A Driver Remote Metering Side A Driver Output Power Side A Driver Output Power Rtn J10-1 J10-2 1V full scale at 1kΩ source resistance Side B Driver Remote Met
Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections Figure 2-2: Amplifier Array Remote Interface Panel Amplifier Array Assembly Remote Metering (A1) UHF Amp Tray Refl Pwr (A1) Reflected Power Rtn J5-2 J5-1 1V full scale at 1kΩ source resistance (A1) UHF Amp Tray Fwrd Pwr (A1) Forward Power Rtn J5-4 J5-3 1V full scale at 1kΩ source resistance (A2) UHF Amp Tray Refl Pwr (A2) Reflected Power Rtn J5-6 J5-5 1V full scale at 1kΩ source resistance (A2) UHF Amp Tray Fwrd
Digital UHF Transmitter Chapter 3, Installation and Setup Procedures Chapter 3 Installation and Setup Procedures There are special considerations that need to be taken into account before the DT835A 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.
Digital UHF Transmitter Chapter 3, Installation and Setup Procedures 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.
Digital UHF Transmitter Chapter 3, Installation and Setup Procedures where dirt, leaves or snow will not be carried in with the cooling air. 5. The exhaust should be located as high as possible. Some ducting is usually required to insure the complete flushing of heated air with no stagnant areas. 6. The filter area must be adequate to insure a maximum air velocity of 300 feet per minute through the filter. This is not a conservative number but a never-exceed number.
Digital UHF Transmitter Chapter 3, Installation and Setup Procedures Figure 3-1. 1 kW Minimum Ventilation Configuration 3.2 Unpacking the Cabinets and Trays around the cabinets. Do not remove any labeling or tags from any cables or connectors. These are identification markers that make reassembly of the transmitter much easier. Note: Air conditioning and any related heat exhaust ducts should be in place before continuing with the installation of the transmitter. 3.
Digital UHF Transmitter Chapter 3, Installation and Setup Procedures If trays are pre-mounted in the exciter cabinet, remove the two L-brackets, mounted on the front panel rails of the single exciter cabinet, which hold the trays in place during shipment. The UHF amplifier trays are shipped separately from the amplifier array cabinets because of the weight of each tray. The trays are mounted in the cabinet using Chassis Trak cabinet slides.
Digital UHF Transmitter Chapter 3, Installation and Setup Procedures 3. Verify that the circuit breaker (CB1), located on the rear of the tray, and the main circuit breaker for the system are off. assembly, exciter cabinet (1245-1500), near the center, right-hand side, rear portion of cabinet #1. Connect terminal 1 to line 1, terminal 3 to line 2 (208/240 VAC), and terminal 2 to the chassis ground. 4.
Digital UHF Transmitter Chapter 3, Installation and Setup Procedures Table 3-2: Jumper Positions in the Gain 1 and Gain 2 Circuits for an Input Level of Between –6 and –26 dBm IF Input Range W3 on J4 and W4 on J5 W5 on J6 and W6 on J7 -11 to -6 dBm Low Low -16 to -11 dBm Low High -21 to -16 dBm High Low -26 to -21 dBm High High 3.6 Setup and Operation Procedures automatically cause the transmitter to revert to Standby.
Digital UHF Transmitter Chapter 3, Installation and Setup Procedures for the system and needs to be checked and corrected. A center bullet missing from the 1-5/8" or 3-1/8" rigid coax lines or loose bolts on the connections can cause this problem. Return the Operate/Standby switch to Standby. very similar.
Digital UHF Transmitter Chapter 4, Circuit Descriptions Chapter 4 Circuit Descriptions 4.1 (A1) UHF Exciter Assembly The (A1) UHF Exciter Assembly contains (A1) a UHF Exciter Tray (1142445), (A4 & A5) two Variable Gain/Phase Trays (1245-1200), (A6) a Metering Panel (1061456), (A8) an AC Distribution Assembly, Exciter (12451500) and (A9) a Remote Interface Assembly (1061198). The (A1) UHF Exciter Tray (1142445), takes the Digital IF Input that is upconverted to the On Channel RF by mixing it with a L.O.
Digital UHF Transmitter which has a jumper connected between Pins 1 & 2, that provides the Interlock to the Exciter needed to operate the Transmitter. If the Jumper is missing, the Transmitter will not switch to Operate. If remote connections are made to the Transmitter, they should be made through the plugs provided in the Installation Material as noted on the Interconnect Drawing (1056919 or 1278-8400) for the Single UHF Exciter. 4.1.
Digital UHF Transmitter the FPGA. The output of the pulse shaping filters is then applied to a PreDistortion Linearizer chip, U4, which can be used to correct for nonlinearities in the data transmission path. The output of the Pre-Distortion chip is gain scaled and output to a dual D/A converter that output a baseband I and Q analog signal. 4.2.1.
Digital UHF Transmitter The x8 circuitry consists of three identical x2 broadband frequency doublers. The input signal at the fundamental frequency is fed through a 6-dB pad consisting of R21, R24, and R25 to amplifier U3. The output of the amplifier stage is directed through a bandpass filter consisting of L8 and C32, which is tuned to the fundamental frequency (67 MHz to 132 MHz). The voltage measured at TP1 is typically +.6 VDC.
Digital UHF Transmitter will occur, thus lowering the temperature of the assembly. The +12 VDC enters the board at J2 and is filtered by L1 and C1 before it is applied to the remaining circuits on the board. 4.3.4 (A13) PLL Board (1286-1104; Appendix D) The PLL board is part of the phase lock loop (PLL) circuit, which provides the automatic frequency control (AFC) voltage, that connects to the VCXO assembly, and maintains the accurate output frequency of the VCXO.
Digital UHF Transmitter applies the external 10-MHz reference signal to U1 for use in the PLL circuits. Internal 10-MHz Reference Circuitry The internally generated 10-MHz reference signal connects from jack J7 on the board to pins 3 and 6 of relay K1. If the external 10-MHz reference is missing, or the interlock is not present at J8, pin 1, the relay is de-energized. The internally generated 10-MHz reference connects through the closed contact of the relay from pin 3 to pin 1 to amplifier U1.
Digital UHF Transmitter On, the drain goes low and removes the high to pin 1 of J1, which is connected to the Lock LED, on the LED display board, which is extinguished. Chapter 4, Circuit Descriptions much larger in amplitude than the inphase IF. When these paths are combined in Z1, they provide the required adjustable phase correction to the IF signal. Voltage Requirements The ±12 VDC needed for the operation of the board enters through jack J11.
Digital UHF Transmitter Chapter 4, Circuit Descriptions through the L-pad is lowered, causing black stretch. to the IF signal by controlling the attenuation through the path. Two reference voltages are utilized in the corrector stages and both are derived from the +12 VDC line. Zener diode VR1, with R46 as a dropping resistor, provides +6.8 VDC from the +12 VDC line. Diodes CR11 and CR12 provide a .
Digital UHF Transmitter attenuation through the L-pad is lowered, causing signal stretch, which is the amount of stretch determined by the adjustment of R35. Chapter 4, Circuit Descriptions Disable position; this will move the breakpoint past sync tip so that it will have no affect on the signal. 4.3.6.3 Output Circuit The signal is next applied to amplifier U5 to compensate for the loss in level through the L-pad.
Digital UHF Transmitter de-energized, it connects the receiver IF input at J1, if present, to 50 watts. When K3 is de-energized, it connects to the modulator IF input at J32 and from there to the rest of the board. At this point, the Modulator Enable LED DS5 will be lit. 4.3.7.2 Receiver Selected With the receiver selected, J11-10 and J11-28, which are on the rear of the UHF exciter tray and connect to J30 on the board, are not connected together; relays K3 and K4 are energized.
Digital UHF Transmitter path from the -12 VDC line, through the red Input Level Fault Indicator LED DS1 (which lights), resistor R54, and transistor Q2 to +12 VDC. The high from U9A also connects through diode CR16 to U9B, pin 5, whose output at pin 7 goes high. The high connects through range adjust pot R74 to J20, which connects to the front panelmounted power adjust pot. This high connects to U10A, pin 2, which causes it to go low at output U10A, pin 1.
Digital UHF Transmitter value resistor. The larger current flow increases the voltage drop across R9 and tends to turn off the diodes CR1 and CR2, causing them to act as highvalue resistors. In this case, the shunt elements act as high resistance and the series element acts as low resistance, which represents the minimum loss condition of the attenuator, maximum signal output. The other extreme case occurs as the voltage at TP1 is reduced, going towards ground or even slightly negative.
Digital UHF Transmitter reference voltage is then connected to diode CR5 through choke L11. Chokes L11 and L12 form a high impedance for the RF that serves to isolate the op-amp ICs from the IF. After the signal is amplified by U2, it is applied to the second corrector stage through T2. This corrector and the third corrector operate in the same fashion as the first. All three corrector stages are independent and do not interact with each other.
Digital UHF Transmitter transmitter is accomplished, if the (optional) remote power raise/lower kit (1227-1039) is purchased, by R75, a motor-driven pot controlled by switch S1 on the board or screwdriver adjust pot R1 on the front panel of the UHF exciter tray. An external power raise/lower switch can be used by connecting it to jack J10, at J10-11 power raise, J10-13 power raise/lower return, and J10-12 power lower on the rear of the UHF exciter tray.
Digital UHF Transmitter R81 and C61. When the transistor section of U11 is on, -12 VDC is also connected through CR22 to the pindiode attenuator circuit. This establishes a very fast muting action, by reverse biasing CR3, in the event of an external VSWR fault. Chapter 4, Circuit Descriptions up a detector circuit. The detected signal is amplified by U6B and its output is split. One amplified output of U6B connects to the digital level circuit, the other output is not used in digital operation. 4.3.8.
Digital UHF Transmitter the board. The +12 VDC also connects to U5, a 5-VDC regulator that provides the voltage needed to operate U4. The -12 VDC is applied to J5, pin 1, and is isolated and filtered by L5 and C35 before it is connected to the rest of the board. 4.3.9 (A11) UHF Upconverter Board (1265-1310; Appendix D) The UHF upconverter board provides upconversion processing by mixing the IF and LO signals in mixer Z1 to produce the desired RF frequency output.
Digital UHF Transmitter variable attenuator in which each pin diode functions as a voltage-variable resistor that depends on the DC bias supplied to the diode for the resistance value. The pin diodes, because of a large, intrinsic region, cannot rectify signals at this RF frequency; therefore, they act as a linear voltage-variable resistor. The pin diodes are configured in shunt configuration: CR1 is the first shunt element, CR2 is the second shunt element, and CR5 is the series element.
Digital UHF Transmitter transmitter, as needed, to maintain a maximum of 20% VSWR. An interlock (low) must be present at J8-24 for the transmitter to be switched to Operate and, when the interlock is present, the green Interlock LED DS5 will be lit. 4.3.10.1 Operate/Standby Switch K1 is a magnetic latching relay that controls the switching of the transmitter from Operate and Standby.
Digital UHF Transmitter low. The low is applied to J8-7 and this will enable any remote auto indicator that is connected to it. The low to Q23 biases it off and removes the enable to any remote manual indicator connected to J8-6. When switch S2 is set to the Manual position, the operation of the transmitter is no longer controlled by the fault circuits; it is controlled by Operate/ Standby switch S1.
Digital UHF Transmitter only function if a receiver tray is part of the system. The overtemperature fault is controlled by the temperature of the reject load. Modulation Loss Fault If a modulation loss occurs while the transmitter is in Auto, the system will go to Standby after a few seconds until the modulation is returned. The transmitter will immediately revert to Operate. An input loss fault applies a low from the ALC board to the fault input at J7-5 on the board.
Digital UHF Transmitter sample that is split is connected to U2B, pin 5. If the reflected sample level increases above the level set by R22, the VSWR cutback pot, the output of U2B at pin 7 goes high. The high is connected to Q11 through CR11, which is biased on, making U2C, pin 10, low and causing U2C, pin 8, to go low. This low is split and fed out of the tray at J1-6, J1-7, J1-8, and J1-9; these are ALC outputs to the amplifier trays that cut back the output power of the amplifier trays.
Digital UHF Transmitter amplifier U1A and 100-Ω resistor R87 to position 2 of switch S3. The ALC sample connects to the board at J6-1 and is connected through buffer amplifier U2C; R15, the ALC calibration pot that adjusts the output of U2A, pin 1; through 100-Ω resistor R18; and to position 1 on switch S3.
Digital UHF Transmitter lit if +12 VDC is present to J6; C3 and C4 are bypass capacitors. The +12VDC output of U2 connects to J3, pins 1, 2, 3, and 4, which is another one of the +12-VDC outputs of the board. The green LED DS2 will be lit if +12 VDC is present to J3; C5 and C6 are bypass capacitors. 4.3.11.
Digital UHF Transmitter panel mounted ALC adjust Pot (A8) connects through (A5) the Metering Board (1245-1202) to J5 on the Board which controls the output level to the tray. A front panel mounted Phase adjust Pot (A7) connects through the Metering Board to J4 on the Variable Phase/Gain Board which controls the phasing of the RF output. The Phasing adjust is needed to phase the two RF outputs of the Amplifier Arrays, when they are combined, to achieve maximum output.
Digital UHF Transmitter The (A13) Front Panel Meter is for Combined Output Power that is controlled by (S1) the Meter Control Switch, the (A15) Front Panel Meter is for Side A Output Power with (S2) the Meter Control Switch and the (A17) Front Panel Meter is for Side B Output Power with (S3) the Meter Control Switch. 4.5.
Digital UHF Transmitter front panel meter. Another input to the (A9) Dual Peak Detector Module is the Forward Sample from the Side A Amplifier Array which is peak detected and connected to the (A15) front panel meter. 4.5.4 (A18) Detector Threshold Board (1245-1402; Appendix D) The Detector Threshold Board consists of three identical signal paths.
Digital UHF Transmitter by capacitor C1 and bypassed by C2 to prevent oscillations. The filtered +12 VDC is applied to U1 a 7812 IC voltage regulator and current limiter. C3 is a bypass capacitor to prevent oscillations in the output DC lines. DS1 is a Green LED which when lit indicates that the +12VDC is present at the output of the board. The +12 VDC is distributed thru Pins 2 & 7 of each of the Output Jacks, J1, J2, J3 & J4, to the rest of the boards in the Tray.
Digital UHF Transmitter six outputs of the splitter are used, depending on output power, (A1 thru A6) UHF Amplifier Trays (1281-1100), the number used depending on the output power needed, (A7) a 4, 5 or 6 Way Combiner, depending on the output power needed, (A8) an Output Coupler (1016-1043), (A10) an AC Distribution Assembly (1278-1200) for Single Phase AC Input or (1278-1100) for Three Phase AC Input and (A11) an Interface Panel. If the Amplifier Array contains the 2.
Digital UHF Transmitter the Amplifier Array contains an External Exhaust Kit, then a Fan Enable is supplied at J4-19 with +12V at J4-20 that connect to the fan mounted on the roof which turns it on.. Main AC Input Each Amplifier Assembly needs an AC Input of 208/240 VAC at 100 Amps Single Phase or 208/240 VAC at 55 Amps Three Phase wired to it.
Digital UHF Transmitter Chapter 4, Circuit Descriptions as the heatsink, for the 1-watt UHF amplifier board (1227-1303) that is mounted inside the assembly. Depending on the frequency of the channel of operation, the assembly has approximately 9 dB of gain. connected across R3, VR1, VR2, R1, and R2, which sets the base bias voltage at +.8 VDC and forward biases Q1. C6, L1, and L2 provide RF decoupling of the bias voltage before it is connected to the base.
Digital UHF Transmitter parallel transistors that make up Q1. The base circuit is RF bypassed by C2, C7, C17, C28, and C29. The collectors are impedance matched to 12.5Ω by C22, C23, and C19, which can be adjusted for peak output with the best linearity. C25 provides AC coupling and DC blocking for the output signal to SMA RF output connector J2. L2 and its associated circuitry form a balun that transforms the two balanced signals back to a single, unbalanced 50-Ω impedance output.
Digital UHF Transmitter transistors in parallel and operating Class A, which amplify the signal by approximately +11 dB. Bias adjust pot R6 sets the operating current for Q1. Q1 and Associated Circuitry The RF input signal connects to SMA jack J1 on the board. The RF input is applied through AC coupling and DC blocking capacitor C1 to L1 and associated circuitry. This forms a balun that converts the input signal from a 50-Ω unbalanced impedance to a 12.
Digital UHF Transmitter current that was fed through R11 and Q1 to flow more through Q2, from collector to the emitter ground, and setting up the negative feedback path. The negative feedback tends to stabilize the current flow through Q1. Capacitor C8 provides an active filtering action for this current source, which provides an improved response in Q1 during the vertical interval average current changes that take place. 4.8.4.
Digital UHF Transmitter network consisting of R7, R9, and adjustable resistor R6. R6 is adjusted to set up the operating current at 5 amps. When the opto-isolator LED turns on, it causes the transistor portion to also turn on. When the transistor portion turns on, it biases on Q2, which acts as a shunt regulator for the base current of Q1.
Digital UHF Transmitter sensitive to changes in the video level. A sample of the forward power is tapped off by R6 and R8 and fed to J3, the forward sample output jack. Diode CR2 provides temperature compensation for diode CR1. An input signal level of approximately +17 dBm is enough to give a 1-VDC level at the output of U1C. A reflected output power sample enters the board at SMA jack J2. Resistors R18, R19, and R20 form an input impedance-matching network of 50Ω.
Digital UHF Transmitter generic dual stage amplifier board, Class AB (1265-1404). The board uses two PTB20101 Ericsson transistors in parallel-biased Class AB to amplify the signal by approximately +9 dB. Bias adjust R106 sets the idling current for Q101 at 300 mA and bias adjust R206 sets the idling current for Q201 at 300 mA. Each dual amplifier device is mounted in identical, parallel circuits. These devices may be biased up to 600 mA depending on the linearity of the tray.
Digital UHF Transmitter The collector voltage is applied at E201. The collector voltage is connected through R208 to the collectors on the two devices that make up Q201. R206 can be adjusted to set up the operating currents. The collector circuit is RF bypassed by C212 to C215, C217, C218, C221, C224, C230, and C231.
Digital UHF Transmitter The bias voltage to the bases of the paralleled transistors, Q201, is applied at E201. The transistors are protected from overvoltage by Q202, Q203, R204, R205, and R206, which can be adjusted to set the bias, operating currents of the transistors. The base voltage is RF bypassed by C229, C202, C207, C208, C209, and C210 and applied to the bases through R202 and R203. The collectors are impedance matched to 12.
Digital UHF Transmitter The collector voltage is applied at E101. The collector voltage is connected through R108 to the collectors on the two devices that make up Q101. R106 can be adjusted to set up the operating currents. The collector circuit is RF bypassed by C112 to C115, C117, C118, C121, C124, C130, and C131. Q201 and Associated Circuitry The other output of the splitter is applied through AC coupling and DC blocking capacitor C201 to L201 and associated circuitry.
Digital UHF Transmitter Chapter 4, Circuit Descriptions Table 4-1: Fuses, Idling Currents, and Voltage Settings for the Class AB Amplifier Devices SWITCH POSITION AMPLIFIER MODULE TRANSISTOR DEVICE BIAS ADJUST POT IDLING CURRENT VOLTAGE SETTING FUSE I1 A4-A1 Q1 R6 *5 Amps 50 mV F1 I2 A4-A3 Q201 R206 600 mA 6.0 mV F2 I3 A4-A3 Q101 R106 600 mA 6.0 mV F3 I4 A5-A2 Q201 R206 300 mA 3.0 mV F4 I5 A5-A2 Q101 R106 300 mA 3.0 mV F5 I6 A5-A3 Q201 R206 300 mA 3.
Digital UHF Transmitter Overtemperature LED DS3 on the front panel is lit. 4.8.12.1 Phase Control The phase control pot on the front of the tray connects to J8-1 (+26 VDC), J8-3 (phase I/P), and J8-4 (RTN) on the board. The phase-control output connects from J7 on the board to the input of the phase-control circuit on the variable gain/phase board (12651425). 4.8.12.
Digital UHF Transmitter amplifier. The output of U1A is split, with one part going to the AGC circuits, another sample connected to J1-5 for remote metering, and the final sample applied to the meter at position 3 on S2, the front panel meter switch. R2 can be adjusted to calibrate the % Forward Power indication on the front panel meter. A sample of the reflected power output of the tray is applied to jack J2-1 and J2-2 of the board from the dual peak detector board, single supply.
Digital UHF Transmitter output when the input signal level drops below a threshold set by R16, R17, and CR5. This high is applied to the red Input Fault LED DS1, which lights to indicate an input fault. DS1 can be seen through the hole in the lid on the variable gain/phase assembly. The high is also connected to the gate of Q1, which biases it on and causes its drain to go low. The low is applied to the pin-diode attenuator circuit consisting of CR1, CR2, and CR3.
Digital UHF Transmitter combiners. Two of the RF inputs to the board are soldered directly to the inputs for the 2-way combiner that contains R5. R5 is a balancing resistor in which any RF due to mismatching in the combiner will be dissipated. The other two RF inputs are soldered directly to the 2-way combiner that contains R6. R6 is a balancing resistor in which any RF due to mismatching in the combiner will be dissipated.
Digital UHF Transmitter and CB7 are 20 Amp Circuit Breakers that are added to the AC Distribution Assembly when the two extra UHF Amplifier Trays are needed for the 5 kW and 6 kW Transmitters. CB6 is a 20 Amp Circuit Breaker which protects the AC connected through J5 on the AC Distribution Assembly to J4 on the (A5) UHF Amplifier Tray. CB7 is a 20 Amp Circuit Breaker which protects the AC connected through J6 on the AC Distribution Assembly to J4 on the (A6) UHF Amplifier Tray. 4.
Digital UHF Transmitter The heatsink and the fans cool the Assembly while the thermal switches provide overtemperature protection for the Transmitter, if the temperature of the heatsink raises above 175°F. Chapter 4, Circuit Descriptions 4.11.1 (A12-A2) Combiner Reject Load Board, (1278-1311; Appendix D) The Board is made up of 6 “N” connectors to which 50 ohm 400 Watt load resistors are connected. This completes the description of the 23kW Amplifier Array and the DT835A Transmitter. DT835A, Rev.
Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures Chapter 5 Detailed Alignment Procedures This transmitter was aligned at the factory and should not require additional alignments to achieve normal operation. Switch on the main AC and the UHF exciter circuit breakers on the AC distribution panel behind the rear door of the exciter cabinet. This transmitter operates using a MPEG digital input.
Digital UHF Transmitter IF Input Range -5 to 0 dBm -10 to -5 dBm Chapter 5, Detailed Alignment Procedures Table 5-3: Jumper Positions on the 6-dB Pad 6-dB Pad W1 on J23 & W2 on J27 Enable 2-3 2-3 Disable 1-2 1-2 5.2 (A4) UHF Exciter Tray (12941111; Appendix C) local oscillator chain tuning and the local oscillator center frequency tuning. Both of these were completed at the factory and should not require adjustments at this time.
Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures receiver tray is present in the system. DS5 is always on with no receiver. The ALC is muted when the transmitter is in Standby. To monitor the ALC, turn off the four amplifier on/off circuit breakers on the AC input assembly in the rear of the cabinet and switch the transmitter to Operate. Adjust the power adjust gain pot on the front panel of the UHF exciter tray to obtain +0.8 VDC on the front panel meter in the ALC position.
Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures 5.2.2 IF Phase Corrector Adjustment output signal. A typical digital spectrum is shown in Figure 5-1. There are three corrector stages on the IF phase corrector board, each with a magnitude and a threshold adjustment which are adjusted as needed to correct for any intermod problems. Adjust the R3 threshold for the cut in point of the correction and the R7 magnitude for the amount of the correction that is needed.
Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures 5.2.3 (A15-A1) UHF Generator Board (1565-1109) frequencies must be minimized to prevent interference with other channels. The (A15-A1) UHF generator board is mounted in (A15) the UHF generator enclosure. This procedure should be performed to align this board.
Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures Table 5-5: Switch Positions SWITCH SW1-8 SW1-7 SW1-6 SW1-5 POSITION N5 N4 N3 N2 SW2-8 SW2-7 SW2-6 SW2-5 N1 N0 A5 A4 SW3-8 SW3-7 SW3-6 SW3-5 A3 A2 A1 A0 Table 5-6 shows the proper switch positions according to channel frequencies. Note: N7 and N6 are fixed values and can not be programmed.
Digital UHF Transmitter CHANNEL 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 FREQUENCY (MHz) 673 679 685 691 697 703 709 715 721 727 733 739 745 751 757 763 769 775 781 787 793 799 805 811 817 823 829 835 841 847 Chapter 5, Detailed Alignment Procedures N N7-N0 A A5-A0 84 84 85 86 87 87 88 89 90 90 91 92 93 93 94 95 96 96 97 98 99 99 100 101 102 102 103 104 105 105 01010100 01010100 01010101 01010110 01010111 01010111 01011000 01011001 01011010 01011010
Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures 5.3.1 (A2-A1) Variable Gain/Phase Board (1265-1425; Appendix D) 5.3.5 (A4-A2) Coupler Board Assembly (1227-1316; Appendix D) The board is mounted in (A2) the variable gain/phase enclosure. The board has an AGC adjustable gain of 0 to 20 dB. There are no adjustments to this board. 5.3.6 (A4-A3) Dual Stage Amplifier Assembly, Class AB (1265-1413, low band/1265-1411, mid band/12651420, high band; Appendix D) 5.3.
Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures 1404) with a frequency determining kit. These boards operate class AB and have a gain of approximately 9 dB. The idling current for each of the transistors is set to 100 mA digital. Connect a sweep test signal to J1, the RF input jack of the UHF amplifier tray.
Digital UHF Transmitter 5.3.12 (A7) Amplifier Protection Board (1265-1412; Appendix D) There are no adjustments to this board. 5.3.13 (A8) Amplifier Control Board (1265-1414; Appendix D) To check the operation of the overdrive circuit, increase the gain pot of the UHF amplifier tray to approximately 110%. The Overdrive LED DS2 should light and the output power should not increase above the 110% level. If the LED does not light, adjust R71 the overdrive threshold as needed until the LED lights. 5.3.
Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures Amplifier Tray for 50% output power and adjust the Phase control to mid range. 4. Monitor the output power of the Transmitter by connecting a Spectrum Analyzer to the Sample Jack located on the Metering Panel. Adjust the Spectrum Analyzer for Zero Span operation. The power could be monitored by watching the meters on the panel but the power change is easier to see on the analyzer. 5.
Digital UHF Transmitter (1159965). Adjust R9 for 100% on the Side A Power Meter. Side B Forward Power Calibration. In (A6) the Metering Control Panel, located in the UHF Exciter Cabinet, find the (A8) Dual Peak Detector Board (1159965). Adjust R9 for 100% on the Side B Power Meter. 5.6 Calibration of the Side A and Side B Amplifier Arrays Reflected Output Level Monitor the Side A Power Meter, in the Forward Power position, and turn the power adjust pot, located on the (A4) Phase/Gain Tray, to 20%.
Digital UHF Transmitter measurement instrument), adjust the output power for a reading of 2000, 2500 or 3000 watts on the true average power meter. Adjust R28 on (A10) the visual/aural metering board in the metering panel for 100% in the % Combined Output Power position. Set pot R20 on (A10) the visual/aural metering board full CCW. 5.
APPENDIX A SAMPLE LOG REPORT SHEET
Digital UHF Transmitter Appendix A, Sample Log Report Sheet (A1) Single UHF Exciter Assembly (A1-A6) DT835A Metering Panel Combined Forward (0 - 120%)=_____________% Reject (0 - 120%)=_____________% Reflected (0 - 120%)=____________% (A2) Amplifier Array Side A Forward (0 - 120%)=____________% Reflected (0 - 120%)=____________% (A3) Amplifier Array Side B Forward (0 - 120%)=____________% Reflected (0 - 120%)=____________% (A1-A1) UHF Exciter Tray % Exciter (0 - 120%)=___________% ALC (0 - 1 V)=____
Digital UHF Transmitter Appendix A, Sample Log Report Sheet (A2 and A3) Amplifier Array Assemblies Two amplifier arrays with four, five or six UHF amplifier trays each (A2) Side A (A2-A1) AGC Voltage =_________V % Reflected =_________% % Output Forward =_________% Power Supply =__________V (A2-A2) AGC Voltage =_________V % Reflected =_________% % Output Forward =_________% Power Supply =__________V (A2-A3) AGC Voltage =_________V % Reflected =_________% % Output Forward =_________% Power Supply =_______
Digital UHF Transmitter Appendix A, Sample Log Report Sheet (A3) Side B (A3-A1) AGC Voltage =_________V % Reflected =_________% % Output Forward =_________% Power Supply =__________V (A3-A2) AGC Voltage =_________V % Reflected =_________% % Output Forward =_________% Power Supply =__________V (A3-A3) AGC Voltage =_________V % Reflected =_________% % Output Forward =_________% Power Supply =__________V (A3-A4) AGC Voltage =_________V % Reflected =_________% % Output Forward =_________% Power Supply =___
APPENDIX B TYPICAL OPERATIONAL READINGS
Digital UHF Transmitter Appendix B, Typical Operational Readings (A1) Single UHF Exciter Assembly (A1-A6) DT835A Metering Panel Combined Forward (0 - 120%) = ≈100 % Reject (0 - 120%) = <5% Reflected (0 - 120%) = <5% (A2) Amplifier Array Side A Forward (0 - 120%) = The level as needed to attain the desired output power of the transmitter Reflected (0 - 120%) = <5% (A3) Amplifier Array Side B Forward (0 - 120%) = The level as needed to attain the desired output power of the transmitter Reflected (0 - 1
Digital UHF Transmitter Appendix B, Typical Operational Readings (A2 and A3) Amplifier Array Assemblies Two amplifier arrays, each with four, five or six UHF amplifier trays (A2-A1) (A2) Side A (A2-A2) AGC Voltage = 1 V - 2 V AGC Voltage = 1 V - 2 V % Reflected = <5% with all trays operating % Reflected = <5% with all trays operating % Output Forward = The level is as needed to attain the desired output power from the transmitter % Output Forward = The level is as needed to attain the desired outp
Digital UHF Transmitter (A3-A1) Appendix B, Typical Operational Readings (A3) Side B (A3-A2) AGC Voltage = 1 V - 2 V AGC Voltage = 1 V - 2 V % Reflected = <5% with all trays operating % Reflected = <5% with all trays operating % Output Forward = The level is as needed to attain the desired output power from the transmitter % Output Forward = The level is as needed to attain the desired output power from the transmitter Power Supply = 26.5 V Power Supply = 26.
APPENDIX C ASSEMBLY DRAWINGS
Digital UHF Transmitter Appendix C, Assembly Drawings and Parts Lists DT835A Transmitter Racking Plan ..................................................................... 1142231 Transmitter Interconnect ..................................................................... 1056920 UHF Exciter Assembly Interconnect....................................................................................... 1056919 AC Distribution Assembly, Exciter Assembly Interconnect...........................................
APPENDIX C SUBASSEMBLY DRAWINGS
Digital UHF Transmitter Appendix D, Subassembly Drawings and Parts Lists UHF Filter Schematic........................................................................................ 1007-3101 ±12V Power Supply Board Schematic........................................................................................ 1062-3013 General Purpose +12V Power Supply Board Schematic........................................................................................
Digital UHF Transmitter Appendix D, Subassembly Drawings and Parts Lists Visual/Aural Metering Board Schematic........................................................................................ 1265-3309 UHF Upconverter Board Schematic........................................................................................ 1265-3310 Transmitter Control Board Schematic........................................................................................
Digital UHF Transmitter Appendix D, Subassembly Drawings and Parts Lists Dual Stage Amplifier Assembly, Class AB, High Band Made from a Generic Dual Stage Amplifier Board, Class AB (1265-1404). Schematic........................................................................................ 1265-3441 Combiner Reject Load Board Schematic........................................................................................ 1278-3311 PLL Board Schematic......................................................
APPENDIX D DT835A SYSTEM SPECIFICATIONS
Solid State DTV Transmitters DT835A-3, DT835A-4, DT835A-5, DT835A-6 The DT800A Series is a full line of low and medium power UHF DTV transmitters. This time proven design offers high performance and simplicity in a very compact unit. Solid state digital output power levels are available up to 3 kilowatts average while tube type versions offer up to 5 kilowatts average.
DT835A-3, DT835A-4, DT835A-5, DT835A-6 Performance Output Power (average) 1500 / 2000 / 2500 / 3000 Watts 470 to 806MHz Frequency Range1 Output Impedance 50 ohms Frequency Stability ±1KHz (max 30 day variation) w/Precise Frequency Option ±2Hz Regulation of RF Output Power 3% Out of Band - Compliant with FCC Mask2 Channel Edge ±500KHz -47dB or better 6MHz from Channel Edge -110dB or better Signal to Noise (SNR) 27dB or better Data Interface Input Rate 19.39Mbps.
