How To Measure RF Signal Peak Power Levels

This is a photograph of WiPry-Combo measuring pulsed RF power collected by a 2.4 GHz “Wi-Fi” antenna from an ASUS PC motherboard. The antenna connects to the WiPry-Combo device through a coaxial cable using one of the SMB-to-SMA connectors in Oscium’s Conducted Measurement Kit. The antenna that ships with each WiPry device is similarly tuned to 2.4 GHz, but this setup answers the question “What if I need to measure signal strength using my own antenna?” The answer of course is “Yes, you can!” Now the ASUS antenna is 2.4 GHz, but don't forget that the range for the power meter is 100 MHz to 2.7 GHz.. Power measurements can be made for any frequency across this spectrum, provided that the antenna is tuned to the desired frequency. The WiPry-Combo spectrum analyzer device can be used anywhere a traditional peak power meter is used, except that Oscium’s handheld tool is more convenient.

Power Meter Setup and Instrument Settings

For this photograph, the Oscium WiPry-Combo device is switched to power meter mode, and is paired with an Apple iPad2. The trigger level is set high enough that low power signals are ignored, and the power meter is used in single-shot mode (a feature included with a newer version of the WiPry App) so only one pulse train is captured. WiPry-Combo is a capable device that can measure lengthy series of pulses train (sometimes called a pulse train), or measure with precision the characteristics of individual pulses. For the WiPry software to perform calculations like Period, Frequency, and Duty Cycle, the user must expand the time scale to display multiple cycles of the periodic waveform on the screen. For example, the jagged waveform displayed in the picture is really a series of sharp pulses transitioning faster than the measurement resolution allows. If the user wanted to study the characteristics of an individual pulse, or a pair of pulses, then he or she must decrease the time scale in order to achieve the necessary resolution on the screen. This can easily be done by pinching and zooming into the waveform. Timescales can be increased or decreased by pinching horizontally on the screen. There’s a tradeoff for consideration between the measured precision and the time span measured. Oscium’s WiPry user interface allows multiple instrument configurations to be saved and recalled, making it that much easier for users to see both the forest and the trees.