Nautel XL12 Technical Instructions

Contents

12 000 WATT AM BROADCAST TRANSMITTERXL12Page 2-2301 January 20022.3.5 AUDIO PASS BAND SELECTION:The interphase PDM driver PWBs (A1A5 forexciter 'A' and A1A6 for exciter 'B' on the exciterpanel) have provision to select one of four audio passbands. Refer to the interphase PDM driver PWBs.The selection is determined by the settings of theirAUDIO FILTER switch (S1). The user must determinethe most suitable roll-off frequency from the fourchoices tabulated in table 2-3 and then set the AUDIOFILTER switch for each PWB accordingly. Thefactory default selection is for a -1.0dB roll-off at thehighest frequency. This selection will be adequatefor most installations.NOTEA 3-pole Butterworth filter that can be alteredtowards a pseudo-Bessel response is used as thelow-pass audio filter.The decision to select a lower roll-off frequencywill be dictated by complex factors. They mayinclude an antenna with sideband limitations,square wave overshoot, and the processing theaudio is subjected to. In some instances, AMstereo stations may wish to reduce/eliminate passband influence. Nautel's field service departmentwill provide advice and recommendations basedon the installation.(a) Refer to table 2-3 to determine the roll-offfrequencies that can be selected and thesettings of the AUDIO FILTER switch that arerequired to obtain them. Record the selectedroll-off frequency and the AUDIO FILTER switchsettings for future reference.(b) Set or verify the AUDIO FILTER switch, on bothinterphase PDM driver PWB's, has been set toprovide the desired high-frequency roll off, asrecorded in step (a).NOTEThe optimum variable pulse duration modulationfrequency (ƒPDM) was selected during factorytests. Refer to the Transmitter ConfigurationSheet, provided with the Factory Test Results, todetermine switch settings that were established toobtain this frequency. These settings should beused unless the assigned carrier frequency ischanged.Table 2-3 Audio Pass Band SelectionHIGH FREQ AUDIO FILTERROLL-OFF SWITCH SETTINGS(-1.0 dB) S1-1 S1-216.0 kHz CLOSED CLOSED13.5 kHz OPEN CLOSED10.5 kHz CLOSED OPEN7.5 kHz OPEN OPEN2.3.6 AUDIO CHOICES: The AUDIO SOURCEswitch on the exciter panel's interface PWB must beset to reflect the type of audio and number of audioinputs that are applied to the transmitter. Paragraph2.1.6 identifies the audio input options which areavailable.2.3.6.1 Refer to paragraphs 2.1.6.1 thru 2.1.6.4 toidentify which exciter/audio input option is in use andthen set or verify the exciter interface PWB's AUDIOSOURCE switch has been set to the setting identifiedfor that option.2.3.7 REMOTE CONTROL CHOICES:Remote control input circuits must be configured toreflect the type of inputs that are applied to them.Paragraphs 2.1.8 and 2.1.9 identify the functions thatcan be controlled remotely and what their connectionoptions are. Refer to paragraphs 2.1.8.1 thru 2.1.8.6and 2.1.9.1 to identify which remote control inputsare being applied and then determine which areconnected to apply a differential input and which areconnected to apply a single-ended input.2.3.7.1 Differential Inputs: Install a 2-socketshunt post in the DIFFERENTIAL INPUT position (pins 1and 2 shorted) of the 3-pin header identified as beingassociated with each control that applies adifferential input.2.3.7.2 Single Ended Inputs: Install a 2-socketshunt post in the SINGLE ENDED INPUT position (pins 2and 3 shorted) of the 3-pin header identified as beingassociated with each control that applies a singleended input.