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Antenna Matching |
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Matching 28 ohm design antennas to 50 ohm coax |
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Some of the newer designed Yagi have an impedance different than 50 ohm. On this site there are antennas with an impedance of 28 ohms. These can be matched using conventions methods or you can just use two parallel 1/4 wavelengths of 75 ohm coax. This will transform the 28 ohms impedance to 50 ohm impedance good for your RG-8. On another page is a calculator to determine the length of coax at a given frequency (remember to use the velocity factor when computing the length).
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Stacking Antennas |
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Whenever you stack antennas the impedance will change (two 50 ohm antennas will give 25 ohms). You match these antennas using 1/4 wavelenght coax to transform one impedance to another impedance. If you stack two 50 ohm antennas you can match them by transforming the 50 antenna to 100 ohms at the coax feed point and 2 - 100 ohms in parallel gives you 50 ohms at the feed point. You have to use odd numbers of 1/4 wavelength to use this method. A lot of antennas are stacked 1 wavelenght apart so the 1/4 wavelength will be too short (you will need to use 3/4 of a wavelenght, etc.) |
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