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Joel Koltner wrote:
Radiation resistance is a virtual resistance and does not contribute thermal or Johnson noise. Certainly, agreed. But the loss resistance of the antenna itself is still contributing kTB, right? If I take a small loop of wire that has, say, a 100 milliohms of resistance, it still generates kTB watts of thermal noise power. Why isn't this a "problem?" Because that noise power has a source impedance of 100 milliohms, which is dramatically mismatched to the input impedance of a normal receiver. This is explained in Wes Hayward's full-length textbook, 'Introduction to Radio Frequency Design' (now re-published by ARRL). -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
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