Nautel XR12 Troubleshooting Manual

Also see for XR12: Installation manual Operation and maintenance manual Preinstallation manual

Contents

XR12 Troubleshooting Manual Detailed Circuit DescriptionsPage 2-20 Issue 3.0 2009-07-28RF power module (NAP34A)See electrical schematics Figures SD-19 and SD-20.The RF power module is effectively two wideband RF amplifiers for the AM broadcast frequencyband (530 - 1710 kHz). The RF power module consists of an RF drive control PWB, an RF drivetuning assembly, a modulator input/output PWB and duplicated assemblies for the two widebandamplifiers.Each wideband amplifier contains two power blocks (A/B or C/D) that share an RF outputtransformer. A power block consists of a modulator assembly, a modulator filter, a PA input/outputPWB and two RF amplifier sections.RF drive control pwbSee electrical schematics Figures SD-21 through SD-23.The RF drive control PWB (A1) performs a number of functions. They include:• Buffering, amplifying and tuning the RF drive• Monitoring RF drive level and tuned status• Verifying PA volts is representative of the carrier level and modulation information con-tained in the PDM signals• Splitting and distributing the PDM signals• Monitoring the temperature of the RF amplifier's heat sinks• Generating alarm signals for visual display of fault conditions when a failure occurs• Inhibiting RF output when a failure occurs that would exceed the stress threshold of theMOSFETs in the RF amplifiersRF drive amplifierThe RF drive amplifier is a class 'D' switching mode amplifier. It buffers and amplifies the low levelRF drive applied between J4-5 and J4-2. The resultant (0 - 62 V, approximately) square wave, at thecarrier frequency (fc ), is applied to C38 and C39, which form the first pole of the RF drive tuningfilter. The secondary of T2 provides an RF drive sample at TP15 that represents its currentwaveform.