Nautel XR12 Troubleshooting Manual

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

Contents

XR12 Troubleshooting Manual Detailed Circuit DescriptionsIssue 3.0 2009-07-28 Page 2-31RF drive buffer PWB (NAPE77A/01)See electrical schematic Figure SD-30.The 0 - 15 V RF carrier frequency signals generated by the RF synthesizer PWBs are applied to theRF Drive A (J1) and B (J2) inputs. The active RF Drive signal, as selected by relay K1, is applied toMOSFET drivers U2A through U5A . The buffer amplified RF Drive signals are applied to the RFpower modules. An identical test signal is provided on the RF DRIVE (TEST) output (J5).A sample of the active RF Drive input is peak detected by diode CR1, resistor R5 and capacitor C1and applied to the inverting input of operational amplifier U1A. During normal operation, this dcvoltage is greater than the threshold voltage (4.2 V) applied to U1A’s non-inverting input. U1A’soutput is 0 V, which turns off transistor Q1. The RF Drive Fail output (J3-8) is open collector (non-alarm state). If the RF drive signal becomes too low or disappears, the voltage applied to U1A’sinverting inputs is below the 4.2 V on the non-inverting input. U1A’s output switches to 15 V, whichturns on transistor Q1. The RF Drive Fail output (J3-8) switches to a current-sink-to-ground (alarmstate). This alarm signal is applied to the control/display PWB via the distribution PWB and exciterinterface PWB. A SENSITIVITY jumper (E3) is provided to change the level required to cause an RFDrive Fail alarm. If the transmitter is configured for IBOC, this jumper should be set to LOW(shorting pins 2 and 3).The IBOC phase input, if used, is applied to the RF Phase In inputs [J14 -5 (+) and J14-4 (-)]. Thesignal is applied through RF transformer T1 and inverters U12A and U12 D, where it is connected toboth RF Drive A and B signal paths. Shorting jumpers E1 and E2 must be set in the EXT position(shorting pins 2 and 3) for IBOC use.