Vna smith chart full#
It has full-scale accuracy of ± 5%, quick-change connectors, and a full range of plug-in elements (modules) to provide a wide choice of frequency ranges (450 kHz to 2.7 GHz) and power levels (100 mW to 10 kW). It can be left in the line for continuous monitoring of either the transmitter power output or the amount reflected by the antenna. Q: What’s a typical directional-coupler VSWR meter look like?Ī: The Bird 43 Wattmeter is a widely used, basic insertion-type instrument designed to measure both forward and reflected power in coaxial transmission lines under any load condition (Figure 2). The SWR meter’s impedance must also match the line’s impedance (typically 50 or 75 ohms), so some SWR meters have switches or adapters that select or match the impedance. Q: What’s the limit of the basic SWR meter?Ī: An SWR meter does not measure the actual impedance of a load (the resistance and reactance) but only the mismatch ratio. The meter cannot be left in the circuit during normal operation of the transmitter, This type of VSWR measurement is normally done during set-up or development but only as needed. Using a test instrument and supplying a low-power stimulus to the load or system.These VSWR meters often stay in the line during normal operation to monitor current readings to indicate a change in conditions or a fault. These are usually made with a transmitter operating at a reasonable level of power. VSWR measurements made using power from the transmitter.Q: When and where is this directional coupler used? Directional couplers are frequency sensitive, so the VSWR meter must operate on the frequencies that are needed. The all-analog approach is very effective and cost-effective. (Image: Wikipedia)Ī: The coupler then implements a “calculation” which yields the VSWR number this calculation can be done using all-analog circuitry or via more complicated A/D converters and a processor executing math algorithms. Fig 1: The VSWR meter is based on a directional sampling of the energy in the forward and reflected directions. Two couplers are used, either one for each direction or just one can be used and be switched between directions. This approach samples a small amount of power in one direction and then uses a diode to rectify this, after which it is applied to a meter. Q: What’s the easiest way to measure VSWR?Ī: The basis of a VSWR meter is the directional coupler (Figure 1). Other applications which involve interfacing one RF section of a smartphone to another may need to know the actual impedance. Q: What do engineers and users need to know?Ī: For some applications, such as connecting a transmitter to an antenna, it is often enough to know just the VSWR. This section looks at two approaches to measuring impedance and VSWR. The previous section looked at the basics of VSWR. Understanding the role and implications of impedance in RF transmission lines and antennas is vital to successful system performance.