Nautel Vector-LP VR125 Technical Instruction Manual

Contents

Page 6-20 Vector-LP Radio Beacon Transmitter Technical Instruction ManualIssue 1.1 Section 6 Theory of Operation6.5.2.6.3 Audio LimitingU10:B, U10:C, U10:D, Q7, and theirassociated components form the audiolimiter. The limiter will raise an alarm atU10:13 when the audio signal goes above apre-defined threshold. It will then compressthe audio signal by adjusting the resistanceacross the JFET Q7. This is accomplished byadjusting the JFET’s base voltage at theoutput of the comparators U10:B and U10:C.6.5.2.7 Audio MonitorU1:B and T1 condition the forward powersample signal to produce an audio monitorsignal that can be used to view the modulatedsignal being output by the transmitter.6.5.3 Front Panel MeteringThe front panel of the exciter control/monitorassembly provides local controls and agraphic user interface to display operatingstatus, root cause fault detection, RF power,and critical dc voltage/current levels. Thecontroller/display PWB is mounted on therear of the panel. The front panel is dividedinto three sections – system diagram,diagnostic display and control.6.5.3.1 SYSTEM DIAGRAMThe system diagram is a functional flowdiagram of the transmitter. Each section ofthe flow diagram contains an alarm lamp,which turns on when a fault occurs in thatsection. If a lamp is flashing, the transmitterhas entered a cutback (reduced power) modeof operation. The lamp that is flashing is likelythe cause for the cutback.6.5.3.2 DIAGNOSTIC DISPLAYThe diagnostic display is a graphic userinterface (GUI) screen that is navigated usingfive associated soft-keys. The majority of thetransmitter’s local control (exciter selection,power level, etc.) and monitoring (criticalparameter levels, alarm events, etc.) may beperformed from menus on this display. Ananalog meter is provided, which can displayforward power, reflected power, modulationpercentage or antenna current.6.5.3.3 CONTROL SWITCHESThe control switches determine thetransmitter’s control location (local or remote)and its RF status (on or off).6.5.3.3.1 Local/Remote SelectionWhen Local is selected, all remote controlfunctions, except RF off, are disabled andhave no influence on the transmitter'soperating status or pre-set RF power levels.When Remote is selected, all front panelcontrol functions, except RF Off, are disabledand have no influence on the transmitter'soperating status or pre-set RF power levels.6.5.3.3.2 RF On/RF Off SelectionWhen RF On is selected (enabled in Localmode only), the transmitter’s RF power stageis enabled to provide an RF output. When RFOff is selected (enabled in Local andRemote modes), the transmitter’s RF powerstage is inhibited.6.5.3.3.3 Power Increase/DecreaseWhen Power Increase is pressed (enabled inLocal mode only), the transmitter’s RF outputpower is increased. When Power Decreaseis pressed (enabled in Local mode only), thetransmitter’s RF output power is decreased.Additionally, if both the Power Increase andPower Decrease switches are depressedsimultaneously, the transmitter’s RF outputpower will be reduced to 0 W.