![]() ![]() And I find it easier to swap out toroids than to try to remove or add turns while the toroid is mounted on the board. This makes it easier to play with spacing to get a targeted inductance. Rather than adding or subtracting turns on one toroid I wind two toroids with different number of turns. Often you have to decide whether to use n turns or n + 1 turns on a toroid. The calculated inductance for toroids is not always close to actual value due to winding spacing and toroid material variance. There are various discussions on accuracy but it will get you in the right ball park. Premeasure the inductors and capacitors with the nanoVNA at the frequency of interest before using in the matching network. ![]() The nanoVNA measured high reactance impedances better than standard antenna analyzers designed mainly for SWR measurements. The readings were affected not accurate and consistent. There was just too much RFI from the laptop and power supply that was being picked up by the antenna. Some of my initial measurements where performed with the nanoVNA connected to a computer using nanoSaver software. When measuring ZL impedance use the nanoVNA by itself and use its file saving capability to retain the. If needed, I could remove the 10 pF and substitute a 5 pF or 15 pF capacitor to fine tune the match. I mounted a 47 pF NP0 ceramic SMT capacitor in the BNC connector itself, followed by a 15 pF and 10 pF parallel NP0 SMT capacitors on the protoboard that the matching network was built on. ![]() The mounted BNC showed around 7 pF capacitance, leaving about 71 pF of additional capacitance. I also measured the capacitance of the BNC connector using the nanoVNA and verifying with an autozeroing small capacitance meter. This made me decide to use a set of parallel capacitors so I could fine tune the value that will provide a close match, this turned out to be a good decision. Large changes in capacitor value will prevent the match to be close to the chart center, no matter the value of the inductor. Changes in the capacitor value keeps the network from moving along the 50 ohm constant resistance curve to the center. The most sensitive value seemed to be the capacitor. Thus most RF circuit analysis software includes a Smith chart option for the display of results and all but the simplest impedance measuring instruments can plot measured results on a Smith chart display.Initially I looked at how the match varies with changes in the component values. While the use of paper Smith charts for solving the complex mathematics involved in matching problems has been largely replaced by software based methods, the Smith chart is still a very useful method of showing how RF parameters behave at one or more frequencies, an alternative to using tabular information. However, the remainder is still mathematically relevant, being used, for example, in oscillator design and stability analysis. : 93–103 The Smith chart is most frequently used at or within the unity radius region. The Smith chart can be used to simultaneously display multiple parameters including impedances, admittances, reflection coefficients, S n n scattering parameters, noise figure circles, constant gain contours and regions for unconditional stability, including mechanical vibrations analysis. Smith (1905–1987) and independently by Mizuhashi Tosaku, is a graphical calculator or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits. ![]()
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