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LMR400 has a copperclad aluminum center conductor. LMR400 is often considered a modern replacement for older Belden 9913. LMR400 is lighter in weight and easier to manufacture. However, at most frequencies the Belden 9913 has a tiny advantage in slightly less loss compared to LMR400. The LMR400 dielectric is basically foam which makes it more rugged than Belden 9913. Belden 9913 has a solid copper center conductor. The dielectric of Belden 9913 is a thin tube of polyethylene and a thin spiral of polyethylene holding the center conductor in place. This makes it slightly less lossy than LMR400, however, the difference is not really significant.