![]() This would indicate a 50-ohm load with little reactance or capacitance. Let's look at one antenna, and the differences in the chart. To the top you're adding an inductive load, and to the bottom it's more capacitive. To the right and you increase resistance to a point where it's an open circuit. To the left and you start to drop the resistance until it becomes a dead short. Ideally, you want your RF network to be right in the middle of the chart. Remember that Y=1/Z=1/(R+jX), so that G=1/R only if X=0, and B=-1/X only if R=0. Admittances add together for shunt-connected circuits. Keep in mind that B=jwC for a capacitor, and B=1/jwL for an inductor. But, many circuits have elements connected in parallel or "shunt" that are the acceptance value of admittance (Y) and its constituent values of conductance (G) and susceptance (B), where Y=G+jB. Resistance and reactance represent an opposition to series connected circuits where impedances add together. For example, RG-8 coax is 52.0 ohms.īut why chart it? We normall look at impedance as values of resistance and reactance. Transmission lines have a characteristic impedance, or Zo, that is the square root of the inductance/meter divided by the square root of the capacitance per meter of the cable. Now that you have read the fluff, let's get into the meat of the Smith Chart. However you can also find web sites where you can buy the paper already printed. If you click on the picture of the chart above, you'll get a PDF that you can download and print. Regardless of who invented it, it's a great visual method for calculating RF networks and seeing what the outcome may be. If you browse the Internet you'll also find references to a Japanese engineer named Kurakawa who also created a chart like the Smith Chart about a year before. So in a way, I owe my livelyhood to Carl. As I was watching Carl I mused, "how do you know what coil to change to make the change in the field?" Carl looked at me, told the other guys to go take lunch, and I received a lesson in antenna design, the Smith Chart, and antenna phasers from "the master". My part, and that of others, were to run the radials of the station and report signal readings. ![]() I was working at a radio station in 1968 and was watching him tune a six tower array that was slightly askew. Carl was an expert in AM directional antennas.Īs a side note, I have great admiration for Carl E. It was't until about twenty years ago when I started researching the chart did I find the truth. ![]() In my younger days I was told that Carl Smith, of the consulting engineering firm Smith Electronics, Cleveland, Ohio, was the inventor. The Smith Chart was created by an RF engineer at R.C.A. Understanding The Smith Chart Understanding The Smith Chart
0 Comments
Leave a Reply. |