Talk:Johnson–Nyquist noise

message: There are two statements in this section
"The root mean square (rms) of the voltage, \bar v_{n}, is given by..."
"The root mean square (rms) of the voltage, v_{n}, is given by..."
I understand the difference in the formulas (the former is per sqrt(Hz) ), but the terminology is confusing. --agr 11:31, 17 October 2006 (UTC)
replies: text: The first one is incorrect.   Hanspi's diff of today added the formula for volts per root hertz, and his diff comment calls it power spectral density, which is the square root of actually.  But he didn't fix the text. Dicklyon 15:22, 17 October 2006 (UTC)

text: That would imply a peak that is four standard deviations from the mean, which is not how a Gaussian process works.  In fact, the peak factor is essentially infinite for a Gaussian process, or is a random variable with an unboundedly increasing expectation the longer you wait.  But stepping back, can you say what question your quotes here were intended to address? Dicklyon 06:43, 21 October 2006 (UTC)

text: Yes, if you use the effective R in both cases, they are equivalent (Norton vs Thevenin models).  But if you just use the resistor value and you're hooked up to something with its own impedance that you don't take into account, you'll get the wrong answer. Dicklyon 19:00, 16 February 2007 (UTC)

text: No, I don't mean they have the same effective R.  I mean that IF they have the same effective R, then they have the same RC, same noise bandwidth, and same noise.  The R comes from a Norton or Thevenin equivalent of the circuit connected to the C.  So a series RC connected to a voltage source, or a parallel RC connected to a current source have the same noise.  A series RC and a parallel RC connected both to the same source, of whatever impedance, can never have the same effective R if the two circuits have the same R, because the impedance of the source modifies them in different ways. Dicklyon 00:55, 18 February 2007 (UTC)
thread_title: Noise voltage and power

message: This article seems to imply that noise from Caps is equivalent to noise from Resistors.  I'm not sure that this is true, given the earlier teachings on the benefits (noise) of switched-capacitor filters.  Maybe an explanation of the paradox is necessary. Petersk 16:41, 12 April 2007 (UTC)
replies: text: Why do you think it's not true?  Check any book on switch-cap filter noise analysis. Dicklyon 18:36, 12 April 2007 (UTC)
thread_title: Switched Capacitor Filters

message: What am I missing here?  As previously stated the Johnson-Nyquist noise at room temperature in a 6MHz bandwidth is -106dBm.  With a receiver noise figure of 3dB the receiver noise power would then be -103dBm.  With a receiver noise figure of 1dB the noise power would be -105dBm.  Where do you get -112dBm?
"For example a 6 MHz wide channel such as a television channel received signal would compete with the tiny amount of power generated by room temperature in the input stages of the receiver, which, for a TV receiver with a noise figure of 3 dB would be −106 dBm, or one fortieth of a picowatt. For a TV with a noise figure of 1 dB, the noise power would be −112 dBm."
--Golden Eternity (talk) 21:13, 28 May 2010 (UTC)
thread_title:  6MHz BW Receiver Noise Power Calculations 

message: From the "Noise voltage and power" section, the following statement is confusing: "For the general case, the above definition applies to". There is not a definition above the sentence (it is the first section). If it's referring to shot noise, it should just say the "For the general case, the above definition of shot noise applies to" to remain clear.  —Preceding unsigned comment added by 70.133.83.60 (talk) 21:06, 16 June 2010 (UTC)
replies: text: Agreed. Also, the page starts defining Johnson noise by saying it isn't shot noise. This is confusing - most/many readers are unlikely to know what shot noise is, if they're looking up Johnson noise. Then there is that confusing section about radiation resistance further down - why are we trying to define radiation resistance here, when it has a perfectly good page of it's own? this page needs work - if nobody else gets there first, I'll try to tidy it up a bit at the weekend. GyroMagician (talk) 11:18, 17 June 2010 (UTC)
replies: text: If you look back to 2005, you can see that that statement followed closely after the definition "the noise generated by the equilibrium fluctuations of the electric current inside an electrical conductor."  It made less sense as it drifted further away from what it was referring to.  Dicklyon (talk) 03:09, 18 June 2010 (UTC)
thread_title:  Confusing Text 

message: This does not follow from "the equation above" (which equation?). It is for the case of a matched load. Very misleading.  — Preceding unsigned comment added by Peter1c (talk • contribs) 12:19, 8 May 2013 (UTC)
thread_title:  "From the equation above, noise power in a resistor at room temperature, in dBm, is then ..." =

message: The discution I start here reffers to the following statemant found on the page:
"A resistor in a short circuit dissipates a noise power of" (this line follows a formula of power).
Now I want to put the question -> into what type of power/energy is transformed that power quantity (4*k*T*deltaF).
The word 'dissipation' reffer generaly at transforming work (in various forms, including electrical work) into heat (a type of energy that rises the temperature of things (or changes thier phase -> melding, vaporising)).
The noise power exist all the time and it cannot "dissipate" into heat because otherwise a resistor will heat spontaneosely.
So I suggest that the words: "a circuit disipates a noise power" is not suitable because the noise power does not transform into anything (it does not dissipates, it stays into the device in the same form all the time).
A more intuitive phrase would be: "the circuit present at the terminals a noise power of ... ".  — Preceding unsigned comment added by 84.247.79.142 (talk) 15:51, 4 September 2014 (UTC)
replies: text: In a short circuit with just a resistor, Johnson noise turns heat into electric current, while Joule heating simultaneously turns electric current into heat. These two processes are equal and opposite. ...But anyway I agree with you that the wording needs improvement... :-D --Steve (talk) 01:44, 6 September 2014 (UTC)
thread_title:  Power Dissipation 

message: I think it would be nice to have a separate page called "reset noise" for capacitor reset noise, any objections?
Reasons: One way to derive the thermal reset noise on a capacitor (mean square voltage of kTC) is using Johnson noise, but that's not the only way to derive it. Even basic statistical mechanical arguments work so there is no need for justifying kTC noise with fluctuation-dissipation theorems. Another motivation for the split is that Johnson noise is a dynamically changing noise whereas reset noise is a static fluctuation.
One possible problem is that presently "thermal noise" redirects to this article.--Nanite (talk) 11:13, 15 June 2015 (UTC)
thread_title:  proposal to split off reset noise (kTC) to a different article 

message: I have changed the rather common and derogatory, off-handed remark that Johnson was the "first to measure" to "first to discover and measure."
Johnson did discover it in 1926 (it had clearly not been "predicted" by Nyquist in 1928, as is frequently claimed) it was formulated by Nyquist as a direct result of its discovery/observation by Johnson, who had isolated it sufficiently to understand that it was an intrinsic thermal noise (by comparison, one cannot make the same eponymous claim about Brownian motion, which was completely misunderstood by it's discoverer).  Wikibearwithme (talk) 03:19, 16 September 2016 (UTC)
thread_title:  credit where it is due 

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