I'm not clear on how resistor noise couples into the rest of the circuit. Jim's comments imply that all of the noise voltage from the resistor appears across the 50 ohm input of the receiver. Let's assume that the antenna transmission line has an ideal 50 ohm antenna at one end and an ideal 50 input port to a receiver at the other end. The resistor equivalent circuit for our purposes would be an ideal voltage source in series with a noiseless ideal resistor. When you place this across the transmission line, the noise voltage suffers from the voltage divider that is all these resistors, and so impresses a voltage across the receiver terminals that is scaled by the ratio of the resistors. In other words, Vrx=25 ohms/10Kohms. This implies that the 10K example would put 1.75 nV across the receiver terminals. Is this not the case or do I have it wrong?