Nautel Vector-LP VR125 Technical Instruction Manual

Contents

Vector-LP Radio Beacon Transmitter Technical Instruction Manual Page 4-5Section 4 Testing and Adjustment Issue 1.14.3.5.5 SETTING CHANGEOVER MODEAND RF MONITOR THRESHOLDSIf a standby side is being used, adjust thetransmitter’s high and low RF power limits,low modulation and tone levels, and themonitor delay period, as follows:NOTEInternational Civil Aviation Organization(ICAO) standards dictate the transmitter beturned off or a warning alarm be generatedwhen the RF output decreases by at least3.0 dB or increases by at least 2.0 dB fromthe intended carrier level. The user canalter the monitor settings provided thesecriteria are still met.(a) Disable changeover. Set changeovercontrol to bypass mode (see 3.6.4).(b) Set the transmitter to the desired RFoutput level.(c) Set the transmitter for desiredmodulation depth in ‘beacon’ (PTTinactive) and ‘beacon and voice’ (PTTactive) modes (see 3.6.7).NOTEIf the NDB is to be used only in ‘beacon’ or‘beacon and voice’ mode, you only need toset up the NDB for the appropriate mode.(d) Calculate the desired low modulationdepth for each mode. Set thetransmitter to modulate at these levels.(e) In the Monitor Timeout screen (see3.6.7), set the monitor timeout period(in seconds) and decide whethershutdown will be enabled or disabled.(f) In the Power Thresholds screen (see3.6.7), set the high and low powerlimits and press Compute NewThresholds.(g) In the Mod % Thresholds screen (see3.6.7), press Compute NewThresholds in ‘beacon’ (PTT inactive)and ‘beacon and voice’ (PTT active)modes (see 3.6.7). The thresholdsshould be updated with the desiredvalues.NOTEAt this point the system has automaticallydetermined to use either a current orvoltage sample to control the modulationdetection and protection circuitry.(h) Set the transmitter for desiredmodulation depth in ‘beacon’ (PTTinactive) and ‘beacon and voice’ (PTTactive) modes (see 3.6.7).(i) Enable changeover. Set changeovercontrol to normal mode (see 3.6.4).NOTEChangeover is inhibited when a VSWR of1.4:1 or greater is present.(j) Check each threshold to ensure that itfunctions properly by adjusting thetransmitter beyond the desired limitand observing that the transmitterreacts as expected. For detailedtesting information see 4.3.5.6.NOTEIf you manually decrease the modulationdepth, the transmitter will inhibit outputpower when the tone level is below thedesired threshold. The Keying GateMonitor Fail A or B fault will be displayed.To restore power, increase the modulationlevel and reset the fault status.(k) When complete, restore the transmitterto the desired power level and pressreset to clear all alarms (see 3.6.3).Normal operation should resume.4.3.5.6 VERIFYING EXCITERCHANGEOVER THRESHOLDSVerify the exciter changeover thresholds asfollows:(a) Set the exciter control mode toNORMAL (see 3.6.4). Set KeyerModulation to ON (see 3.6.13.1)