Nautel XL12 Technical Instructions

Contents

12 000 WATT AM BROADCAST TRANSMITTERXL12Page 4-501 January 20024.9.3 RF POWER TRIM: The RF power levelof the selected preset RF power level can beincrementally changed (nominal 1000 increments) byindividually pressing/releasing the RF POWER trim ∧∧(increase) or ∨∨ (decrease) switches. The incrementsare linear voltage steps (power=voltage 2).NOTEIt is recommended the current reading on the DCAMPERES meter and the PA volts reading on theDC VOLTS meter be monitored when increasingthe RF power level. Their readings must not beallowed to exceed the levels previously recordedfor 13.5kW.4.9.3.1 Increase RF Power: Increase RF powerlevel by pressing and releasing RF POWER trim ∧∧(increase) switch, noting a quick press and releasewill increase the RF power level by one increment.If the switch is held, its integral lamp will turn onwhile it is pressed and the RF power will slew in anincreasing direction, after a 0.25s delay, until theswitch is released or until the RF power level is13.5kW. When 13.5kW is attained, the switch'sintegral lamp will turn off, even though the switch isbeing pressed and any further increase in RF powerlevel will be inhibited.NOTEThe RF power trim circuit controls the voltage thatdetermines the carrier level on/off ratio of the PDMsignals, which in turn determine the PA volts levelbeing applied to the RF power amplifiers. Themaximum carrier level on/off ratio that can beattained is 45/55, which translates to 13.5kW when allof the RF power amplifiers are contributing to the RFoutput. If one or more RF power amplifiers is notcontributing, the PA volts that would provide 13.5kWis produced but the forward power level will be lessthan 13.5kW and the DC current reading will decreasein proportion to the change in forward power. Thismethod of control ensures an operator cannotoverdrive the contributing RF power amplifiers whenone or more is not contributing.4.9.3.2 Decrease RF Power: Decrease RF powerlevel by pressing and releasing RF POWER trim ∨∨(increase) switch, noting a quick press and releasewill decrease the RF power level by one increment.If the switch is held, its integral lamp will turn onwhile it is pressed and the RF power will slew in adecreasing direction, after a 0.25 second delay, untilthe switch is released or until the RF power level is0W.NOTEThe RF output should not be set to a level that isless than 1000 watts. Audio distortion andunacceptable signal to noise ratios may resultwith RF power levels of less than 1000 watts.4.9.4 RF ON/OFF SELECTION: The RFpower stage must be turned on before an RF outputcan be produced. Additionally, the RF power stagecan be turned off and the transmitter retained in thestandby status without turning off the AC powersource.4.9.4.1 RF On Selection: The RF power stage isturned on by pressing and releasing the CONTROL - RFON switch. Its integral lamp will turn on and remainon, indicating the RF power stage is enabled. Theintegral lamp of the CONTROL - RF OFF switch willturn off.4.9.4.2 RF Off Selection: The RF power stage isturned off by pressing and releasing the CONTROL -RF OFF switch. Its integral lamp will turn on andremain on, indicating the RF power stage is turnedoff. The integral lamp of the CONTROL - RF ONswitch will turn off.4.9.5 LOCAL/ REMOTE CONTROLSELECTION: The local/remote control selection isdescribed in paragraph 4.8.4.9.6 ADJUST AUDIO LEVEL: The AUDIOGAIN potentiometer on the interphase PDM drivePWBs controls amplitude of the audio signal input tothe transmitter. Turn clockwise to increase audiogain (and modulation depth). Turn counter clockwiseto decrease audio gain (and modulation depth).STATUS DISPLAYS4.10 The control/monitor panel's STATUS displayis provided to assist an operator/maintainer indetermining the present (real-time) status oftransmitter functions and when initiating faultdiagnostics, will identify the cause of the most recentRF shutback. For a brief description of the purposeand function of each display, refer to table 3-1.4.10.1 DISPLAY COLOUR: Each STATUSindicator is a bicolour display. The display will begreen when the associated function/circuit is normal.The display will be red (continuous or flashing)when a failure has been detected or the function isnot operating within defined limits.