Tait TB9100 User Manual

Also see for P25 CG: Installation and operation manual Installation and operation manual

Tait TB9100 User Manual Manual pdf 32 page image

26 Calibrating the Power Amplifier © Tait Electronics Limited February 2007Calibrating the Forward and Reverse Detector Bias VoltagesThe RF detectors, used for measuring the forward and reverse power, operatewith a small bias current. The resulting bias voltage from each detector (withno RF present) is read and stored inside the PA. These voltages are used whencalculating the Antenna VSWR (Voltage Standing Wave Ratio).You should calibrate the forward and reverse detector bias voltages:■ If the Low Pass Filter (LPF)/directional coupler PCB module is replaced■ After servicing of any components in the detector circuitry (such as thedetector diodes) on the LPF/ directional coupler PCBTo calibrate the forward and reverse detector bias voltages1. Make sure that the equipment is set up and that the Calibration Software isconnected to the reciter.2. Select the PA Calibration tab, and double-click Calibrate Fwd/RevDetector Bias Voltages.3. Ensure that the PA is not transmitting and that there is no RF source presentat the PA RF input or output by disconnecting the input SMA connectoron the PA front panel and the ‘N’ type output connector from the rear ofthe PA. Click Calibrate.When you have finished, the icon on the PA Calibration tab indicates thatthis task is complete.Calibrating the PA PowerThe power amplifier (PA) receives the RF signal from the reciter and amplifiesit to the required level, in watts, as requested by the reciter. The desired outputpower is determined by the reference voltage for the power control loop.The PA power control loop is calibrated at a single frequency, generally in thecenter of the operating band.You perform the calibration procedure to define – for each power level – thereference DAC (Digital-to-Analog Converter) value and forward detectorvoltage.You should only need to re-calibrate the PA power if:■ The Low Pass Filter (LPF)/directional coupler PCB module is replaced■ Any repairs are carried out on the forward and reverse detector circuitry onthe Low Pass Filter/directional coupler PCB module■ You require a more accurate power calibration on a specific frequencyEquipment■ Either an inline power meter and 50 ohm load with a high power rating, or■ A terminating power meter and appropriate 50 ohm attenuator with a highpower rating