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How can we experimentally find out value (extent) of Johnson Noise of any resistor with certain bandwidth and teperature?

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Place the resistor in a temperature controlled environment. Measure the nominal resistance (Ohm's law) then connect the resistor to a low noise high gain amplifier whose noise figure is known/calibrated and its input impedance is matched to that of the noise source, here of the resistor. Connect the output to a high quality spectrum analyzer (use an isolator if unsure of the output match) and measure the noise when the input is at room temp, then change the temperature and measure the change in the output noise floor for various settings of the resolution bandwidth (I suggest that you use the calibrated built-in video filter setting). Good luck!

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  • $\begingroup$ Can I simulate this upto high precision level? Suitable simulator/software? $\endgroup$ – learner Dec 24 '19 at 4:41
  • $\begingroup$ Unclear to me what it is that you would like to simulate: the spectrum analyzer's operation or the physics of Johnson noise? If the former, then you can use software Matlab/Simulink, ADS, AWR, etc. If the physics of noise generation interests you then you should ask this on the forum as a separate question, for I cannot help you with it. $\endgroup$ – hyportnex Dec 24 '19 at 12:06
  • $\begingroup$ Please suggest me low noise amplifier I'm thinking of using LT1024 will it suitable or I should choose different one. And I'm using Keithley 195A Digital Multimeter (6 and half) instead of spectrum analyzer will it work for getting the voltage values. I have one more query if I use bandwidth of the DMM as the bandwidth of the circuit will it give appropriate output? $\endgroup$ – learner Jan 7 at 13:28
  • $\begingroup$ It depends on at what frequency you wish to examine the noise. The LT1024 is probably not useful beyond 100kHz, and you also need a bandpass filter between the resistor and the amplifier to limit what you are amplifying, and then a narrow bandpass filter in which you measure the noise power; I doubt that the DMM's own input bandwidth will work, but I do not know. I suggest for these further details you post your question on electronics.stackexchange.com . $\endgroup$ – hyportnex Jan 7 at 13:54
  • $\begingroup$ I'm undergraduate student and I want to do this experiment on my own for better understanding and I don't have much resources I'm trying to keep everything simple so I need simple circuitry which will give me a considerable precise output (surely I won't get precise value equal to theoretical value but I'm trying for somewhat considerable value) as I just want to understand the experiment. $\endgroup$ – learner Jan 7 at 15:05
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If you are talking about the noise current, Wikipédia gives:

$$i_n = \sqrt {{4 k_\text{B} T \Delta f } \over R}.$$

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