RF Power Measurement Basics

Broadcasted on 9/8/2010

View the Recording Download the Slides

Presented by:
Wolfgang Damm, Dir. of Product Marketing

This webinar is designed for people who want to learn about Power measurements with RF power meters.

The main areas covered will include:

Significance of Power Measurements
RF Signal Theory
Vital System Characteristics
Sampling Techniques
Product Specification Examples

These slides are also available in Chinese.

Webinar Q&A

Below are questions we recieved during the webinar. If you have any additional questions, email us.

Can I measure voltage with my power meter?

Yes, this is possible. The conversion from RF to baseband frequencies occurs in the power sensor. When we replace the power sensor with a Boonton voltage probe, the instrument can measure voltage as well. Voltage probes have high impedance and capacities will not be discharged as quickly as with 50Ω power sensors. Voltage probes also have a limited maximum frequency. Boonton offers voltages probes that can be used up to 1.2 GHz.

Can I probe a circuit for power?

Even if we could access certain measurement points, we cannot probe power. To measure power we need to measure both voltage and current at the same time.

Does the power meter output frequency data?

No - power meters are always wide band. They are designed to measure the complete power that is applied to the input of the sensor, independent of the power.

However, for accurate measurements it is recommended to enter the frequency of the signal in the power meter. All sensors are calibrated over their full frequency band. Signal frequency information allows selecting calibration data that is on, or next, to the actual signal. This offers the best measurement accuracy.

Does your sensor fully rectify my output signal?

Yes – Boonton’s sensors are dual diode sensors. Therefore we always measure the complete signal.

Can I average my power measurements to get the same results as random sampling?

If the only parameter you are interested in is average power, you can average over a longer period. Repetitive Random Sampling is used whenever more information is needed; such as a very accurate trace of the original signal to analyze pulses.

What is the maximum carrier frequency I can measure with your system?

The maximum carrier frequency with Boonton sensors is currently 40 GHz.

I already have a crystal detector setup in my lab, why should I change to a peak power system?

Crystal detector setups usually consist of the detector, low pass circuitry, a CW power meter and an Oscilloscope. While this measurement set up is helpful for basic measurements, it will never reach the performance of a peak power meter. Not only is the combination of several components degrading the overall accuracy, but the oscilloscope will never provide the kind of detail a fast power meter with peak sensors can offer.

When speed and accuracy is required a peak power meter is the best measurement solution.

Can I use an average power meter to measure LTE & WiMax signals with changing modulation?

No, for complex noise-like signal forms it is important to know exactly how the power is distributed. This measurement requires a fast sensor (a peak sensor) and the statistical mode of our peak power meters. An average power meter could show that everything is within the limits, but it would not show 2% of the signal is exceeding the allowed input voltage of an amplifier. This is what causes distortion and high BER.

Should I use a peak power meter to measure pulse data signals?

It depends. If you are only interested in measuring average power, slower CW sensors are fine. If you want to analyze the pulse in great detail, fast peak sensor are mandatory. Only this sensor type is fast enough to allow for an authentic re-construction of the original signal on the screen.

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