User's Manual - Crown Broadcast

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4.1 Part NumberingAs this section refers to individual components, you should be familiar with the part numberingscheme used.The circuit boards and component placement drawings use designators such as “R1”, “R2”,and “C1.” These same designators are used throughout the transmitter on several differentcircuit boards and component placement drawings. When referencing a particular componentit is necessary to also reference the circuit board that it is associated with.4-2 FM50/FM150/FM300 User’s <strong>Manual</strong>
4.2 Audio Processor/Stereo Generator Circuit BoardThe audio board provides the control functions of audio processing-compression, limiting,and expansion, as well as stereo phase-error detection, pre-emphasis and generation of thecomposite stereo signal.Illustration 6-4 and accompanying schematic may be useful to you during this discussion.The overall schematic for the audio board is divided into two sheets; one each for the processorand stereo generator sections of the board.Reference numbers are for the left channel. Where there is a right-channel counterpart, referencenumber are in parenthesis.Illustration 4–1 Audio Processor/Stereo Generator Board4.2.1 Audio Processor SectionAudio input from the XLR connector on the rear panel of the transmitter goes to instrumentamplifier, U2 (U8). Two-bit binary data on the +6 dB and +12 dB control lines sets the gainof U2 (U8) to one of four levels in 6-dB steps. Gain of U2 is determined by R5, R6, or R7(R45, R46, or R47) as selected by analog switch U1.U3 (U9) is a THAT2180 voltage-controlled amplifier with a control-voltage-to-gain constantof 6.1 mV/dB. The 2180 is a current-in/current-out device, so signal voltages at the inputand output will be zero. R11 converts the audio voltage at the output of U2 (U8) to current atthe input of U3 (U9). U3 (U9) output current is converted to audio voltage by U4A (U10A).U4B (U10B) is a unity-gain inverter. When the positive peaks at the output of U4A (U10A) orU4B (U10B) exceeds the gain-reduction threshold, U15 generates a 0.25 Volts-per-dB DCcontrol bias, producing wide-band gain reduction for U3 (U9). The dB-linear allows a frontpaneldisplay of gain control on a linear scale with even distribution of dB.Principles of Operation4-3
Page 1 and 2: FM30/FM150/FM300 Broadcast Transmit
Page 3 and 4: ContentsSection 1- Getting Acquaint
Page 5 and 6: Section 5-Adjustments and Tests 5-1
Page 7 and 8: Section 1—Getting AcquaintedThis
Page 9 and 10: 1.2 Applications and OptionsCrown t
Page 11 and 12: 1.2.4 TranslatorA receiver configur
Page 13 and 14: 1.3 Transmitter/Exciter Specificati
Page 15 and 16: Note: We set voltage and ampere req
Page 17 and 18: Section 2—InstallationThis sectio
Page 19 and 20: Illustration 2-1 Removing the Power
Page 21 and 22: 2.2.3 Battery PowerYour transmitter
Page 23 and 24: 2.3.1 Modulation CompensatorThe Mod
Page 25 and 26: Freq. 74-90 Freq. 88-108 SW1 SW2 Fr
Page 27 and 28: Freq. 74-90 Freq. 88-108 SW1 SW2 Fr
Page 29 and 30: 2.6 Audio Input ConnectionsAttach a
Page 31 and 32: Illustration 2-16 Composite In and
Page 33 and 34: Pin Number Function1. Ground2. FMV
Page 35 and 36: Section 3—OperationThis section p
Page 37 and 38: 3. Verify the following:A. The bott
Page 39 and 40: 3.3 Front Panel Bar-Dot DisplaysBar
Page 41 and 42: 3.7 RF Output ControlSet this contr
Page 43: Section 4—Principles of Operation
Page 47 and 48: Processed, pre-emphasized left and
Page 49 and 50: 4.5 Metering CircuitThe ALC and met
Page 51 and 52: Motherboard Jumper Configuration Ch
Page 53 and 54: 4.8 Voltage Regulator Circuit Board
Page 55 and 56: 4.11 RF Driver (FM150/FM300)The RF
Page 57 and 58: 4.15 Receiver Circuit Board OptionT
Page 59 and 60: Section 5—Adjustments and TestsTh
Page 61 and 62: 5.2.2 Composite OutputYou can make
Page 63 and 64: 5.4.3 SWR CalibrateWhen the Carrier
Page 65 and 66: 5.9 Performance VerificationMeasure
Page 67 and 68: 5.15 Audio DistortionMake distortio
Page 69 and 70: Section 6—Reference DrawingsThe i
Page 71 and 72: MeteringCircuitAudio ProcessorSecti
Page 73 and 74: 6.2 Board Layout and SchematicsIllu
Page 75 and 76: 65581 234571234DWG. NO.REV.56789510
Page 77 and 78: 987654321123456789321121234123DWG.
Page 79 and 80: 23212132543215432154321543215432143
Page 81 and 82: Illustration 6-9 FM Display BoardFM
Page 83 and 84: Illustration 6-10 FM Voltage Regula
Page 85 and 86: Illustration 6-11 FM Power Regulato
Page 87 and 88: R19Illustration 6-12 FM Power Ampli
Page 89 and 90: Illustration 6-13 FM Low Pass Filte
Page 91 and 92: Illustration 6-14 FM RF DriverFM30/
Page 93 and 94: 1 2 3 4 5 6REVISION HISTORYAPPROVAL
Page 95 and 96:
Section 7—Service and SupportWe u
Page 97 and 98:
Crown Broadcast Three Year Limited
Page 99 and 100:
Factory Service InstructionsTo obta
Page 101 and 102:
Transmitter Output EfficiencyRF Pow
Page 103 and 104:
GlossaryThe following pages define
Page 105 and 106:
FETFrequency SynthesizerFMonFSKGain
Page 107 and 108:
Symbols19-kHzlevel adjustment 5-3ph
Page 109 and 110:
M (continued)Monooperation 2-13, 3-
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User's Manual - Crown Broadcast

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