Calculating the load impedance and power consumption at high frequencies in RF circuits is a tedious task. This Design Idea describes a VI (virtual instrument) that provides an easy way to quickly and effectively measure these parameters. You can measure and display the power and impedance of various types of loads, such as resistive or series/parallel tank circuits, at any given frequency. Using National Instruments (www.ni.com) LabVIEW, you can easily modify the VI to accommodate any type of load having any complexity. The virtual RF generator comprises power-supply, amplifier, and load-select/measurement-display modules.
The amplifier module, with as much as 90% efficiency, provides frequencies of 100 kHz to 1 MHz with adjustable ac power applied to the load. The load-select-and-display module provides a sine or square waveform, load-selection type, and adjustment.
Figure 1 shows the VI driving a resistive load. Adjusting the frequency from minimum to maximum has no effect on the output impedance and power. You can download the VI and watch a flash movie describing three examples at www.circuitmentor.com.
Caption
Figure 1 These settings on the virtual instrument measure the impedance and power of a resistive load.
Click here for the illustration:
Figure 1
