UBS Axcera 840A 10,000-watt UHF solid state television transmitter User Manual

UBS-Axcera 10,000-watt UHF solid state television transmitter Instruction manual for use of equipment

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Chapter 4

10-kW UHF Transmitter with Chapter 4, CircuitFeedforward Drive Descriptions840A, Rev. 0 4-1Chapter 4Circuit Descriptions4.1. (A1) Dual 250-WattDriver/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 amplifieseach of the three possible audio inputsand the amplifier circuits that supply thesingle audio output. The balanced audioor the composite audio input is connectedto the board while the subcarrier audio(SCA) input can be connected at thesame time as either of the other twoinputs. The board has the 4.5-MHzvoltage-controlled oscillator (VCO) andthe aural modulation circuitry thatproduces the modulated 4.5-MHz output.The board also contains a phase lock loop(PLL) circuit that maintains the precise4.5-MHz separation between the aural(41.25 MHz) and the visual (45.75 MHz)IF frequencies.Balanced Audio InputThe first of the three possible basebandinputs to the board is a 600Ω-balancedaudio input (+10 dBm) that entersthrough jack J2, pins 1 (+), 2 (GND), and3 (-), and is buffered by U1B and U1C.Diodes CR1 to CR4 protect the inputstages of U1B and U1C if an excessivesignal level is present on the input leadsof jack J2. The outputs of U1B and U1Care applied to differential amplifier U1A;U1A eliminates the common modesignals (hum) on its input leads. Apre-emphasis of 75 ms is provided byR11, C11, and R10 and can be eliminatedby removing jumper W5 on J5. The signalis then applied to amplifier U1D whosegain is controlled by jumper W3 on J11.Jumper W3 on jack J11 is positionedaccording to the input level of the audiosignal (0 or +10 dBm). If the input levelis approximately 0 dBm, the mini-jumpershould be in the high gain positionbetween pins 1 and 2 of jack J11. If theinput level is approximately +10 dBm,the mini-jumper should be in low gainposition between pins 2 and 3 of jackJ11. The balanced audio is thenconnected to buffer amplifier U2A whoseinput level is determined by the setting ofbalanced audio gain pot R13. The outputof the amplifier stage is wired to thesumming point at U2D, pin 13.Composite Audio InputThe second possible audio input to theboard is the composite audio (stereo)input at BNC jacks J3 and J13. The twojacks are loop-through connected; as aresult, the audio can be used in anotherapplication by connecting the unusedjack and removing W4 from J12. JumperW4 on jack J12 provides a 75Ω-inputimpedance when the jumper is betweenpins 1 and 2 of jack J12 and a highimpedance when it is between pins 2 and3. Diodes CR9 to CR12 protect the inputstages of U6A and U6B if an excessivesignal level is applied to the board. Theoutputs of U6A and U6B are applied todifferential amplifier U2C, whicheliminates common mode signals (hum)on its input leads. The composite inputsignal is then applied to amplifier U2B;the gain of this amplifier is controlled bycomposite audio gain pot R17. Thecomposite audio signal is connected tothe summing point at U2D, pin 13.Subcarrier Audio InputThe third possible input to the board isthe SCA input at BNC jack J4. The SCAinput has an input impedance of 75Ω thatcan be eliminated by removing jumperW2 from pins 1 and 2 of J14. The SCAinput is bandpass filtered by C66, C14,R22, C15, C67, and R23 and is fed to
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Document ID112608
Application IDBGMB9M9jpEo5y9LJFhTJMw==
Document DescriptionChapter 4
Short Term ConfidentialNo
Permanent ConfidentialNo
SupercedeNo
Document TypeUser Manual
Display FormatMicrosoft Word - pdf
Filesize31.38kB (392233 bits)
Date Submitted2000-08-09 00:00:00
Date Available2000-09-25 00:00:00
Creation Date2000-08-09 15:57:46
Producing SoftwareAcrobat Distiller 4.0 for Windows
Document Lastmod2000-08-09 15:57:48
Document TitleChapter 4
FCC ID Filing: OUS840A

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