Nautel XL12 Technical Instructions

Contents

12 000 WATT AM BROADCAST TRANSMITTERXL12Page 5-1201 January 2002(c) Place a short circuit between TP4 and groundon the RF drive tuning PWB.(d) Remove the connector from E1 on RF driveamplifier 'A' (A11A1) and connect an RFgenerator between the wire and ground. Setthe RF generator to the transmitter carrierfrequency.(e) Monitor the output of the generator with anoscilloscope and frequency counter and adjustthe RF drive tuning inductor A11L1 for a null involtage on the oscilloscope.(f) Confirm the circuit is tuned by sweeping thefrequency generator below and above thetransmitter carrier frequency and confirming anull at the correct frequency.(g) Remove the test equipment.(h) Install the connector on E1 on RF driveamplifier 'A' (A11A1).(i) Restore the connections on relay assemblyA11A7 by moving the push-on connectorsfrom pin 1 to pin 4 and pin 3 to pin 6.(j) Remove the short circuit between TP4 andground on the RF drive tuning PWB.5.5.21.2 RF Power Module Tuning: The RFpower module tuning procedure ensures the RFpower modules are tuned for optimal operation in thehost transmitter. Tune the RF power modules asfollows:(a) Operate the transmitter into a 50 ohm dummyload at a power level of 1000 watts withoutmodulation.(b) Monitor the RF current being applied to powermodule A with a DC multimeter connected toTP5 'A'.NOTEAn RF power module that has a failed RFamplifier cannot be tuned. Repair module beforeperforming this procedure.(c) Using the screwdriver (Nautel Part# HAZ79)from the transmitter ancillary kit, adjust RFpower module A's RF drive tuning inductor fora minimum reading. Refer to the RF powermodule service instruction booklet for locationof the RF drive tuning inductor.(d) Repeat steps (b) and (c) substituting thecorrect RF drive tuning PWB test points andRF power modules.5.5.21.3 RF Drive Level: The RF drive levelprocedure ensures the correct 22 volt peak-to-peakRF drive voltage is applied to the RF amplifier FETsand the RF drive level detector threshold is properlyset.(a) Turn off the transmitter and remove an RFpower module as described in paragraph 5.6.(b) Place the RF power module on a work benchand carefully remove the black plastic coverfrom an RF amplifier.(c) Place an oscilloscope probe on the gate lead ofQ6 in the RF amplifier. Refer to figure MD-6in the RF power module service instructionmanual for the RF amplifier's assembly detail.(d) Re-install the RF power module in thetransmitter as described in paragraph 5.6.(e) Operate the transmitter at 1000 watts outputpower level from exciter A. Set the EXCITERCONTROL switch on the control interface PWBto AUTO TRANSFER INHIBIT.(f) Adjust the VOLTAGE CONTROL potentiometeron the exciter A RF drive regulated powersupply A11A5 until a reading of 17.7 voltspeak-to-peak is recorded on the oscilloscope.This is the lowest allowable RF drive voltage.If the power supply cannot be adjusted lowenough to achieve 17.7 volts peak-to-peak,adjust it to its lowest voltage.(g) Adjust the RF DRIVE THRESHOLD potentiometeron the RF drive tuning PWB until thetransmitter EXCITER RF DRIVE alarm just turnson.