Nautel Vector-LP VR125 Technical Instruction Manual

Contents

Vector-LP Radio Beacon Transmitter Technical Instruction Manual Page 6-1 (6-2 Blank)Section 6 Theory of Operation Issue 1.1Vector-LP Radio Beacon TransmitterTECHNICAL INSTRUCTION MANUALSection 6 THEORY OF OPERATION6.1 INTRODUCTIONThe theory of operation for the Vector-LPRadio Beacon transmitter is presented inthis section. Frequent reference is made toelectrical schematics (e.g., Figure SD-1).They are located in Section 9 of thismanual. Circuits that are shown onelectrical schematics, but not described inthis section are either beyond the scope ofthis manual or are not used for NDBapplications.6.2 TRANSMITTER OVERVIEWThe transmitter operates at one fixedfrequency in the LF/MF band (190 kHz to535 kHz) or in the MF band (536 kHz to1200 kHz and 1600 kHz to 1800 kHz). Itprovides up to 125 W (VR125) or 250 W(VR250) of continuous carrier power. Itautomatically transmits specific beaconidentification signals at pre-selectedrepetition rates. Special codes may also betransmitted when commanded from anexternal source. Provision is made for localor remote operation of the transmitter aswell as antenna fine-tuning throughcontrols on the transmitter's front panel. Ifthe standby option is purchased, provisionis made for automatic changeover from theselected main side of the transmitter to thestandby side when the selected main side'scritical parameters are not met. Thetransmitter operates from a single phase,47 Hz to 63 Hz ac power supply (170 V to270 V ac for VR250; 90 V to 270 V forVR125), using switch mode powersupplies. A 48 V dc input option (and 24 Vdc for VR125 only) can also bepurchased. Emission is continuous carrier(NON) beacon keyed identification tone(A2A) and beacon with voice (A2A/A3A).Local control/monitoring is done usingfront panel membrane switches and agraphic liquid crystal display. Criticalparameters such as forward power,reflected power and antenna current canalso be displayed on an analog meter onthe front of the transmitter.Remote control and monitoring can beprovided over several optional interfaces.The transmitter also has provision tointerface with a Nautel antenna tuning unit(ATU), using an isolated RS485 serial link.This ATU link allows the transmitter toregulate antenna current, and thereforemaintain constant field strength, by auto-adjusting its output power in accordancewith the ATUs antenna current sample.The transmitter circuitry can berepresented using four functional stages(see Figure 6-1): Ac-Dc Power Stage Exciter Stage Control/Monitor Stage RF Power Stage6.3 AC-DC POWER STAGESee Figures 6-1 and SD-1. The ac-dcpower stage accepts the ac power sourceor optional dc power source and converts itto the necessary low level dc voltagesrequired throughout the transmitter. The acinput voltage is also applied directly to theRF power stage. The ac-dc power stage’sprimary components are the ac-dcuniversal input power supplies (U2 and U3,if used) and the interface PWB (A11). If thedc input option is purchased, thetransmitter also includes the dc-dcuniversal input power supply (U10) and thebattery boost PWB (A16A1).