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Stew Hicks wrote:
For radio experts, I read somewhere that coax should be cut in increments of 1/2 wavelength, for the center of the bandwidth, 1 1/2 meters as I recall. I can't find the article now can anyone verify this? How critical is this? Thanks for any help...............Stew Stew It' is true. But a lot depends on your application as to how critical it is. The reasoning is this: impedacne "inverts"every 1/4 wave, so if you make your coax 1/2 wave increments it "double inverts" which means the impedance is the same at the input end as at the far end. If you had a purely resistive impedance of exactly 50 ohms ( for standard radio transmitter/receivers) you really wouldn't care about length, but being that the impedance of a typical installation is somewhat unpredictable and is almost certainly a complex impedance with both resistive and reactive componets it's best to stick with the 1/2 wave increments. That being said make sure you figure the 1/2 wave in coax not air. IE if the coax is 66% velocity factor you figure the 1/2 wave length in air then multiply by .66 and then make it a multiple of that! Clear as mud? John |
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