Power Measurement with Power Meter and Power Sensor

How to measures the reference signal by power meter, signal is produced by Signal Generator.

Equipment Required For Power Measurement

  • Signal Generator
  • Power Meter
  • End-Line Power Sensor
  • Variable Attenuator
  • Couple Of Cables For Interconnection

Safety precaution

Before starting remember that overloading a device like the power meter may become cause of damages.  Always estimate the power you are going to apply to the device before connecting it and be sure it fits in the accepted range. If you are not sure then adopt a safe setting.Power Measurement with a Power Meter and Power Sensor

Procedure for Power Measurement

There are ten steps to measure the power

  1. Set the signal generator to output a carrier signal with a value of 0 dBm of average power and a frequency of 2.4 GHz. Disable any modulation.
  • Power             0 dBm
  • Frequency     2.4 GHz
  • Modulation    OFF
  1. Connect the power sensor to the power meter following its instructions before switching it on. The general procedure consists in switching on the meter for some time in order to stabilize the temperature of the circuits. Then use the internally generated reference signal to calibrate the gain of the sensor. After the calibration the instrument should not be switched off.
  2. Set the variable attenuator to an attenuation of -20 dB.
  • Attenuation   -20 dB
  1. Check again the output level of the generator (it should be 0 dBm or 1mW) and the attenuation of the variable attenuator (-20 dB). Estimate the losses of the cables at the working frequency and compute the expected power level at the input of the power meter.
Powerexpected(dBm)= PowerGenerated(dBm)+LossesCable(dB)+LossesConnector(dB)+Attenuation(dB)

In our case the expected value cannot exceed -20 dBm.

  1. Be sure that this estimated value fits in the actual measurement range of the power meter setting the range knob.
  2. Connect the signal generator to the power meter passing through the attenuator. Enable the output of the signal generator if it was disabled.
  3. If everything is accurate the power meter should indicate the expected value of the power. If you don’t read the expected value or a near one, switch off immediately the generator and check carefully the connections, the setting of the instruments, the calculations.
  4. You may observe a small difference of the order of a few dB between the estimated and measured value. This difference is given by the losses of the connectors in the RF chain and eventually by the inaccuracy of the instruments. The signal generator is not supposed to be a reference source of power, if not stated explicitly in the manual. You can therefore use this procedure to estimate roughly the losses of the cables and connectors but you cannot expect to get the exact value.
  5. Disable the output of the signal generator if possible or reduce the power at the minimum level then switch the generator off. Disconnect the RF cable from the power sensor but not switch off the power meter.
  6. Repeat the calibration procedure for the power meter in order to validate the measurements. If you notice that the instrument calibration has changed, repeat the whole measurement procedure. Finally switch off the power meter and disconnect the power sensor.