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## Re: [RFI] Paying for information

 To: "Jim Brown" ,"RFI List" Re: [RFI] Paying for information "Tom Rauch" Tom Rauch Tue, 23 Dec 2003 14:20:33 -0500
 ```Hi Jim, I'm not trying to be argumentative about this but.... > But the simple fact is that my work has shown that some of our > assumptions about how cable behaves are incorrect. How much are they > wrong? Braid-shielded cable (Belden 8412 and equivalent) has SCIN > performance that is roughly 30 dB better than foil/drain shielded cable > (Belden 8451 and equivalent) in the AM broadcast band! Here is where you can help. Correct me if I'm wrong. 30 dB is a ratio between the two cables you tested, but if one cable is -140dB based on some outside test to "no shield" and the other cable is -110, who cares? Let me make a statement that is true as an example. Clean shiny pressure-compacted woven braid without an extreme weave (like a cable shield) has about 7 times more loss than a solid wire the same dimensions and material. If I lost one watt in a unit length of solid wire and measuring the same length shield at 7 watts, it would be 8.5dB more loss. 7 times nearly nothing, however, is meaningless. 1000 times nearly nothing can be meaningless. But the ratio between the nothings can be 8.5dB. Saying the common mode problem increases 30dB doesn't mean a thing to me. Unless we know much more. It falls into the category of useless specs people worry about like "shielding effectiveness" of coaxial cables. Ask almost anyone how shielding effectiveness is measured and what it means, and they don't have a clue. That's why so many people waste money on extra shields they don't need. Also, measuring ratios in nulls is a pretty difficult task. There was a "radiation from a Beverage drop wire" attempt to measure the depth of nulls, and there were obvious problems with the test method. There are many things that are almost impossible to measure accurately, let alone are meaningless ratios. I'm not saying you are right or wrong. I'm only saying without knowing how the measurement was done, the results really don't mean anything....and I'm not willing to pay money to make someone else's statement have meaning. 73 Tom _______________________________________________ RFI mailing list RFI@contesting.com http://lists.contesting.com/mailman/listinfo/rfi ```
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