Nautel Vector-LP VR125 Technical Instruction Manual

Contents

Vector-LP Radio Beacon Transmitter Technical Instruction Manual Page 4-11Section 4 Testing and Adjustment Issue 1.1NOTEWhen you exit the Calibrate Meters menu amessage is displayed indicating that youhave made changes. You will be promptedto save the changes to EEPROM so thatthey can be restored in the event of apower failure. Press Yes each time thisprompt is displayed during the setupprocedure.During initial turn-on and adjustment oftransmitter power, the diagnostic display’smeters screen should be monitored.4.3.6.5 CALIBRATING PDM(a) Use an oscilloscope to monitor TP17 ofthe active interphase PDM driver PWB(A6 for side A or A9 for side B).(b) Press RF On. Set modulation to 0%.(c) In the Calibrate Meters menu (see3.6.12 and 3.6.12.1) scroll through theparameters until PDM A (or PDM B,depending on the transmitter’s activeside) is highlighted. Press Modify.(d) Adjust the value to match the positiveduty cycle measured on TP17 in step(a). Press Done.4.3.6.6 CALIBRATING REFLECTEDPOWER THRESHOLD AND OUTPUTNETWORK ALARM(a) Turn off the transmitter and disconnectthe dummy load from the transmitter’sRF output. Short the transmitter’s RFoutput to ground near the RF output.Install the external current probe on theshorting jumper.(b) In the Set Thresholds menu (see3.6.12 and 3.6.12.2) set the SlowbackPwr (Per Block) value to 100 W.(c) Set RF output power to 0 W. Press RFOn. Monitor the external current whileslowly increasing the power to half ofthe reflected power limit. Try to achievea current of 1.8 A (should occur atapproximately 40 W).(d) Calculate the actual reflected powerusing the following equation:Refld Pwr = (Ishort circuit / 2)2 x 50(e) In the Calibrate Meters menu (see3.6.12 and 3.6.12.1) scroll through theparameters until Reflec. Power ishighlighted. The Reflec. Power valueshould be within 20% of the valuedetermined in step (d). Press Modify. Adjust the value to match the levelcalculated in step (d). Press Done.(f) Press Back and select SetThresholds.(g) Press , or Next until Refl. PowerShutback is displayed. Monitor the external current whileslowly increasing the power to thereflected power limit. Try to achieve acurrent of 2.5 A (should occur atapproximately 80 W).(h) If an Output Network alarm occursbefore reaching the reflected powerlimit, increase the Refl. PowerShutback threshold level and pressDone and return to step (h). Otherwisecontinue to step (j).(i) Decrease the Refl. Power Shutbackthreshold level until the OutputNetwork alarm occurs. Press Done.(j) In the Set Thresholds menu, set theSlowback Pwr to 30 W (for VR250) or15 W (for VR125).