Nautel XL12 Technical Instructions

Contents

12 000 WATT AM BROADCAST TRANSMITTERXL12Page 2-3401 January 2002(e) Set the output level of the audio signalgenerator to zero (turned off).(f) Select exciter A. Press/release EXCITER Aswitch noting its integral lamp turns on and theEXCITER B switch's lamp turns off.NOTEIf a C-QUAM AM stereo exciter is installed asexciter A's RF drive source, proceed toparagraph 2.4.6.2 unless it is to be checkedwhen it is set for monaural operation.(g) Repeat steps (a) thru (e) for exciter 'A', payingparticular attention to the caution aboutadjusting the interphase PDM driver PWB'sAUDIO GAIN potentiometer if a C-QUAM AMstereo exciter PWB is exciter A's RF drivesource.(h) Turn off the RF power stage. Press/release RFOFF switch noting its integral lamp turns on andthe RF ON switch's lamp turns off.(i) Disconnect the audio signal generator fromTB2-8(+) and TB2-9(-) on the remoteinterface PWB.2.4.6.2 Modulation Checks (AM StereoOutput): Verify the RF carrier is being phasemodulated by the L-R audio and it is being amplitudemodulated by the L+R audio when a C-QUAM AMstereo exciter is installed as exciter A's RF drivesource and exciter A is active.(a) Select or verify exciter A is selected. Press/release EXCITER A switch noting its integral lampturns on and the EXCITER B switch's lamp turnsoff.(b) Turn off or verify the RF power stage is turnedoff. Press/release RF OFF switch noting itsintegral lamp turns on and the RF ON switch'slamp turns off.(c) Set the exciter interface PWB's AUDIO SOURCEswitch to its STEREO position.(d) Interface an audio signal generator to the leftand right audio inputs of the C-QUAM AMstereo exciter PWB using a test audioswitching circuit as defined in the exciter'sservice instruction manual.(e) Set the C-QUAM AM stereo exciter PWB toproduce an AM stereo output. Set its STEREOENABLE switch to the STEREO position.(f) Turn on the RF power stage. Press/release RFON switch noting its integral lamp turns on andthe RF OFF switch's lamp turns off.(g) Check the function of the C-QUAM AMstereo exciter PWB. Refer to theMaintenance section of its service instructionmanual, noting:- Final testing and adjustments are completedwith the transmitter operating into its antennasystem.- The RF drive output must not be disabled bydisconnecting the RF drive coaxial cable fromthe C-QUAM AM stereo exciter PWB's RFDRIVE connector unless it is necessary to troubleshoot the PWB or a complete functional test isto be completed.NOTEIt will be necessary to inhibit the automaticexciter changeover if the RF drive from the C-QUAM AM stereo exciter PWB is disabled. Setthe system control PWB's Exciter Control switch(S19) to the AUTO XFR INHIBIT position.(h) On completion of testing, turn off the RFpower stage. Press/release RF OFF switchnoting its integral lamp turns on and the RF ONswitch's lamp turns off.(i) Disconnect the test audio switching circuit(including the audio signal generator) from theleft and right audio inputs of the C-QUAM AMstereo exciter PWB.2.4.6.3 Modulation Peak Limiting: Verify themodulation peaks are limited, to reduce RF poweramplifier stress current, when the RF output'smodulation envelope contains low frequency (longduration), high amplitude peaks, as follows:(a) Verify the requirements of paragraphs 2.4.6and 2.4.6.1 have been completed.(b) Connect an oscilloscope between theassociated interphase PDM driver PWB's TP3and ground.