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Owen Duffy wrote:
. . . My objective isn't so much trying to build a better loss model, but rather to use a simple loss model and build the coefficients from manufacturer's published data and make that available in the calculator. . . . Unfortunately, manufacturer's published loss data are often quite different than actual cable loss. Belden RG cable I measured long ago was routinely considerably better than the spec -- apparently the spec was dictated by the MIL SPEC, and the cable was manufactured to never exceed it. More recently, I've found that in trying to convince rather naive amateurs to purchase their cable, some manufacturers are claiming considerably lower loss than the cable actually has. So the bottom line is that manufacturer's published data are just so many numbers, and don't necessarily have any direct relationship to any real cable. Careful scrutiny of real cable will also reveal that the characteristic impedance varies quite a bit, and the velocity factor of foamed dielectric cable is even more variable. Roy Lewallen, W7EL |
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