How to measure power for a low power RF Power Amplifier?

[enjunear]

Since most power supplies will display current and voltage used when connected to the power amplifier, do you think I can just rely on the voltage and current reading on the power supply?

If I use the digital voltmeter to measure the power and connect it to the power amplifier just like the way what you said, I am wondering how accurate the measurement would be, since the digital voltmeter is connected in series between the power supply and the power amplifier.

Thank you.

If you trust the calibration of your power supply's displays (and can deal with a non-ideal result), then yes, you could use them to determine V, I and calculate DC power input to your device. Since this is my industry, we typically use two meters. An ammeter directly after the power supply, and a voltmeter right at the input to the amplifier circuit (between the long wires from the supply, and before the RF choke (inductor). That way you have nearly the exact voltage at the device (eliminates the unknown voltage drop from the power leads), and the current. You might have to tweak your power supply voltage up if your ammeter has a lot of series resistance, but this shouldn't affect you much with a "low power" device.

P.S. An RF power meter, or Spectrum Analyzer (SA) will give you the best RF output power measurement. Make sure you have a DC blocking cap on your output (as mentioned before). If your signal is low power, then I'd lean toward the SA, since they are used to measure things down to the noise floor. In either case, check the maximum input power handling of the device, and use sufficient attenuation (pads) between the amp and device, so you don't blow up your $$$$ test equipment (10 dB or more below Pmax is a good place to start). And if you need attenuation, don't forget to measure the pad's insertion loss, so you can remove it from the measured value and calculate the true output power level.

 

[Syncopator]

Since most power supplies will display current and voltage used when connected to the power amplifier, do you think I can just rely on the voltage and current reading on the power supply?

Measuring the voltage and current to the amplifier will let you calculate the power used, not the power applied to the load.

Not really satisfactory. However, if you have no other instruments available, it's better than no measurement at all.

If I use the digital voltmeter to measure the power and connect it to the power amplifier just like the way what you said, I am wondering how accurate the measurement would be, since the digital voltmeter is connected in series between the power supply and the power amplifier.

No. The voltmeter is across the supply, not in series with it.

Accuracy of what?

As I just said, it will allow you to calculate the power consumed by the amplifier, and that figure is as accurate as that of your measuring instruments.

You can then make, at best, an educated guess at the power delivered to the load.