User's Manual

ManualsBrandsHitachi Kokusai Electric America ManualsElectronics200W UHF ATSC Transmitter - Advanced TV

AT7400 Owner Manual Rev. 2.0 – October 2006-10-23 Section 5 -14/17

7.2. Board CIM3452 Schematic Diagram: SEE ANNEX A

8. GAV4445 - Module 4275 – Power Supply

8.1. Module 4275 – General Functional Description

Module 4275 is a switching high power DC supply, type full-bridge powered by 208 Vac, showing overall

efficiency above 80%. As part of the power supply design, there is a power factor corrector, PFC, circuit.

Besides correct the power factor to close to 1, this circuit also contributes to reduce the harmonic content

returning from the unit into the AC mains.

The sub-module 4275 deliveries two +32V voltage outputs, VA and VB. These two voltages feeds the 75W UHF

amplifiers, sub-module 4451. This sub-module also delivery the +15V for the control unit SCU, CIM 3452,

located on the power drawer.

The module 4275 is composed by the following PCB’s:

Fig.5.9: CIM3429 – Full Bridge Control PCB.

Summary of content (15 pages)

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7.2. Board CIM3452 Schematic Diagram: SEE ANNEX A 8. GAV4445 - Module 4275 – Power Supply 8.1. Module 4275 – General Functional Description Module 4275 is a switching high power DC supply, type full-bridge powered by 208 Vac, showing overall efficiency above 80%. As part of the power supply design, there is a power factor corrector, PFC, circuit. Besides correct the power factor to close to 1, this circuit also contributes to reduce the harmonic content returning from the unit into the AC mains.
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AT7400 GRO UND AC 180 to260V IND U CT OR +18V C IM 3427 PFC C ONT ROL SW IT C HIN G TR AN SIS TORS R ET IFIER TR AN SFOR MER RE TIF IE RS +18V RE GUL AT OR +1 5V R EGU LAT OR Owner Manual Rev. 2.
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8.3. CIM3238 – Power Phase Control Unit – PFC The PFC circuit is located at PCB CIM 3238, at sub-module 4275. The PFC circuit is a power supply built according with the “boost regulator in continuous mode (CCM)” topology. Under the CCM topology, is possible guarantee a power factor, cosφ above than 0.9. The PFC circuit is composed by a full diode bridge that performs a full-wave rectification on the AC signal, which than is routed to the boost inductor. The voltage is so boosted up to +385V.
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On maintenance situation the sub-module 4275 the automatic operation, (independently of the SCU status), AUT, can be turned on a manual MAN, operation by changing the position of the jump CON-3. The AUT position must be re-state as soon as the maintenance is over. The shut down operation is fundamental to protect the power supply and the UHF amplifiers as well, sub-modules 4451. 8.8. Module 4275 – Technical Specifications 8.9. Module 4275 –Schematic Diagrams: SEE ANNEX A AT7400 Owner Manual Rev. 2.
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Section 6 – Output Directional Coupler, UHF Low Pass Filter & Band Pass Mask Filter 6.1. Module 4429 – Output Directional Coupler - General Description The UHF output related power readings direct and reverse, are shown on the LCD screen at the MCU (module 4459) located on the frontal part of the ADVANCED TV line of transmitters. All the readings are RMS values of the 8VSB modulated carrier.
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.2. Module 4429 – Technical Specifications 6.3. Module 4429 – Block Diagram AT7400 Owner Manual Rev. 2.
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6.4. Module 4429 - Drawings AT7400 Owner Manual Rev. 2.
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6.5. Module 4429 – Calibration 6.5.1. Introduction The calibration procedure is quite simple however very important for the overall transmitter operation. Usually this procedure should not take place on the field. The criterions of calibration follow the recommendation as ATSC A53/E. In case of re-calibration, it is mandatory the utilization of absorption type wattmeter. LINEAR utilizes the Agilent model E4418B EPM series single power meter in conjunction with the 8481A power sensor.
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6.5.2. Module 4429 – Calibration Step-by-Step To reach the MAIN MENU screen, Fig.6.4, hit the CANCEL yellow key (not shown below) up to 4 times in sequence, any time. Fig. 6.4: Main menu LCD screen at MCU unit 6.5.2.1 Direct Power Calibration 1. Using the keyboard (soft-keys) and LCD on the MCU, manage to disconnect the ALC operation. Follow the selfexplanatory screen instructions. Start with the main menu screen, striking in sequence the gray keys as going to SETUP →TRANSMIT→ALC→OFF→ENTER. Fig.6.
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2. Adjust the RF power via menu (ALC is OFF at this point) to the desired nominal level read at the calibrated external wattmeter. Fig.6.5: Reference output power reading on the power meter absorption Check if the readings on the LCD screen of the transmitter are also displaying the same value. To get to this screen start out from the main menu and go to SETUP→POWER, reaching the POWER TRANSMITTER SETUP screen as shown on Fig.6.6 below: Fig.6.
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3. To make the power reading coincidence among the 3 readings, (a) the wattmeter, (b) the [program], and (c) [output] where (b) and (c) are present on the LCD screen, will be necessary adjust the DC level that represents the coupling coefficient between the sampler and the 50Ωtransmission line at the output directional coupler hardware. Look for the indication of FORWARD POWER opening the case of the output directional coupler, (Module 4429).
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6.6.1. Module 4428 – UHF Low Pass Filter Fig.6.9: UHF low pass filter The module 4428 is a 7/8” rigid transmission line, no tuning points. Depending of the UHF assigned band the filter is specified as:  P/N 21802 for Channels 14 up to 39: …….....416.5 mm.  P/N 23045 for Channels 40 up to 69: …….….373.3 mm. These filters have NO adjustment to be done. Pay attention for mechanical damages that may occur on the main line, or also on the IN/OUT connectors. Fig.6.
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6.6.2. Module FC6E80C – UHF Band Pass Filter – ATSC Mask Filter Featured AT7400 Owner Manual Rev. 2.
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AT7400 Owner Manual Rev. 2.
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FEATURES • UHF 500W Digital TV band pass filter • ATSC FCC Mask applications • 6 poles elliptical response (cross coupling) • Dual Cross technique (four transmission zeros) • Combline topology • High selectivity and low loss (Typ. 0.