![]() There is some algebra involved in understanding the basic transmission line equations, but - once you understand how to move on the graph - you can forget the math and just read the chart. What Is a Smith Chart?Īlthough there are many computer programs 2, 3 and network analyzers that can solve impedance matching problems for you, a complete understanding of the Smith Chart is highly beneficial in understanding the nature of transmission lines. This chart closely resembles the chart we see today. According to his biography, his impedance coordinates were not orthogonal - which means perpendicular - and there were no true circles, but the standing wave ratio was linear. The first graphical chart was limited by the range of data so he came up with a polar plot that was a scaled version of the first plot. He used a thermocouple bridge and voltmeter to make the measurements. Smith developed the first graphical solution in the form of a rectangular plot from his measurements of the maxima and minima voltages along the transmission line. Phillip Smith - Inventor of the Smith Chart. He relished the problem of matching the transmission line to the antenna a component he considered matched the line to space. Although Smith did a great deal of work with antennas, his expertise and passion focused on transmission lines. In 1928, he joined Bell Labs, where he became involved in the design of antennas for commercial AM broadcasting. Smith attended Tufts College and was an active amateur radio operator with the callsign 1ANB. The Smith Chart was invented by Phillip Smith, who was born in Lexington, MA on April 29, 1905. After reading this, you will have a better understanding of impedance matching and VSWR - common parameters in a radio station. The purpose of this article is to introduce you to the basics of the Smith Chart. (The unit of admittance is the siemen, the reciprocal of the ohm.The Smith Chart is one of the most useful tools in radio communications, but it is often misunderstood. ![]() As will be shown later, it is sometimes easier to work with admittances, the mathematical inverse of impedance. ![]() Measure out from these limiting case values when calculating the appropriate quantity. If the radius was D, or the center of the chart, a reflection coefficient of 0 and an SWR of 1 would be obtained. This time, however, measure the distance frdm the center (SWR = 1). To calculate the SWR, use the same d stance for the scale labeled SWR. The outermost circle of the Smith Chart represents |r| = 1 and the center of the chart is = 0.42 ¿^123°, The radius can be cal-Ĭulated by measuring the distance from the center c f the chart to ZN with a compass and transferring that to the scale at the bottom of the chart labeled transmission coefficient E or I. The angle of r is read from the scale labeled ancle of reflection coefficient in degrees. The radius from the chart's center to another point represents (T|. Using the normalized quantity, ZN, we can obtain plot with a higher degree of accuracy (Fig 5). But let's first use the impedance we calculated earlier We will plot that value on the Smith Chart and calculate several quantities directly from our data This match 3d condition will be our goal in an upcoming example. An impedance plotted at this point would be matched if it was normalized to the Zp of the line. It is the only resistance circle to pass through the center poir|t at 1 + ¡0. Fig 3A shows circles of cons through the center of the chart. Figs 3A and 3B show what the different lines on the Smith Chart represent. Its angle is measured from a scale on the outside of the chart. Where the distance from the center of the chart to any point is the |r|. Radio Electronics 1987-03 Fig 4-When the two types of circles shown in Fig 3 are superimposed on each other, the result is a Smith Chart.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |