Nautel XL12 Technical Instructions

Contents

12 000 WATT AM BROADCAST TRANSMITTERXL12Page 2-2901 January 20022.4.4 RF DRIVE CHECKS: Check thefrequency, symmetry and level of the RF drive forthe 'A' and 'B' exciters as follows:(a) Verify the requirements of paragraph 2.4.3have been completed and are being met.2.4.4.1 RF Drive Frequency: Measure thefrequency of the RF drive being applied to the activeRF drive amplifier:(a) Connect a frequency counter between the leadof R1 identified as TP1 on the active RF driveamplifier and TP2 (ground).(b) The RF drive frequency, as indicated by thefrequency counter, shall be the assigned carrierfrequency ±5.0 Hz or five parts per million(ppm) whichever is greater.(c) If required, adjust the frequency at the activeexciter's RF drive source for precisely theassigned carrier frequency:- If an external RF generator is the RF drivesource adjust its output frequency as directedin its maintenance manual.- If an RF drive PWB is the RF drive source,adjust its FREQ ADJUST variable capacitor (C15).- If a frequency synthesizer PWB is the drivesource, adjust its FREQ TRIM variable capacitor(C30).- If a C-QUAM AM stereo exciter PWB is theRF drive source (exciter 'A' only), adjust its4ƒƒ c variable capacitor (C49).(d) Select exciter A. Press/release EXCITER Aswitch noting its integral lamp turns on and theEXCITER B switch's lamp turns off.(e) Repeat steps (a) thru (c)(f) Disconnect the frequency counter.(g) Return to exciter B. Press/release EXCITER Bswitch noting its integral lamp turns on and theEXCITER A switch's lamp turns off.Figure 2-5 Balanced Drive ƒc Input Waveformƒc = 1700kHz (AC Coupled)2.4.4.2 RF Drive Symmetry: Measure thesymmetry of the RF drive being applied to the activeRF drive amplifier:(a) Connect an oscilloscope between the lead ofR1 identified as TP1 on the active RF driveamplifier and TP2 (ground).(b) Oscilloscope indication should be similar toexample depicted in figure 2-5. It should be asymmetrical (50% duty cycle) square wavewith a nominal amplitude of 15.0 Vpp.(c) If necessary, adjust the RF drive source toobtain a symmetrical square wave:NOTEIf an external RF generator is producing the RFdrive, verify its output waveform is symmetrical.If necessary adjust it as directed in itsmaintenance manual.- If an RF drive PWB is the RF drive source/processor, adjust its SYMMETRY potentiometer(R5).- If a frequency synthesizer PWB is the drivesource/processor, adjust its SLICER BIASpotentiometer (R41).- If a C-QUAM AM stereo exciter PWB is theRF drive source (exciter 'A' only), adjust itsSLICER BIAS potentiometer (R154).