I have been pondering the notation for noise voltage. The noise voltage across a 50 ohm resistor is expressed as 1nV/sqrt(1Hz) As I ponder this it seems to me that one is concerned about the noise voltage period. For instance, if you have a 1Hz BW signal you would say the noise voltage on a 50 ohm resistor is 1nV. If you have a 100 Hz signal you would say that the noise voltage is 10 nV (on a 50 ohm resistor with a 100 Hz BW) Would you say 10 nV/sqrt(100Hz) ? (I don't think so) It seems to me that the notation of 1nV/sqrt(1Hz) is really just a reminder that when calculating the noise voltage that the noise voltage goes up by the square root of the Bandwidth, and is not really relevant other than for the reminder. Agree?

# Question about noise voltage

Started by ●September 7, 2011

Reply by ●September 7, 20112011-09-07

On Sep 7, 9:43�pm, brent <buleg...@columbus.rr.com> wrote:> I have been pondering the notation for noise voltage. �The noise > voltage across a 50 ohm resistor is expressed as 1nV/sqrt(1Hz) > > As I ponder this it seems to me that one is concerned about the noise > voltage period. �For instance, if you have a 1Hz BW signal you would > say the noise voltage on a 50 ohm resistor is 1nV. > > If you have a 100 Hz signal you would say that the noise voltage is 10 > nV (on a 50 ohm resistor with a 100 Hz BW) > > Would you say 10 nV/sqrt(100Hz) ? (I don't think so) > > It seems to me that the notation of 1nV/sqrt(1Hz) is really just a > reminder that when calculating the noise voltage that the noise > voltage goes up by the square root of the Bandwidth, and is not really > relevant other than for the reminder. > > Agree?No.

Reply by ●September 7, 20112011-09-07

On Sep 7, 9:43�pm, brent <buleg...@columbus.rr.com> wrote:> I have been pondering the notation for noise voltage. �The noise > voltage across a 50 ohm resistor is expressed as 1nV/sqrt(1Hz) > > As I ponder this it seems to me that one is concerned about the noise > voltage period. �For instance, if you have a 1Hz BW signal you would > say the noise voltage on a 50 ohm resistor is 1nV. > > If you have a 100 Hz signal you would say that the noise voltage is 10 > nV (on a 50 ohm resistor with a 100 Hz BW) > > Would you say 10 nV/sqrt(100Hz) ? (I don't think so) > > It seems to me that the notation of 1nV/sqrt(1Hz) is really just a > reminder that when calculating the noise voltage that the noise > voltage goes up by the square root of the Bandwidth, and is not really > relevant other than for the reminder. > > Agree?Please ignore this thread and reply to other one. Google took over an hour to post first message so I reposted thinking it was lost -- bah.

Reply by ●September 7, 20112011-09-07

On 9/7/2011 9:43 PM, brent wrote:> I have been pondering the notation for noise voltage. The noise > voltage across a 50 ohm resistor is expressed as 1nV/sqrt(1Hz)Did you just make that up, or did you read it somewhere?> As I ponder this it seems to me that one is concerned about the noise > voltage period.What do you call a voltage period?> For instance, if you have a 1Hz BW signal you would > say the noise voltage on a 50 ohm resistor is 1nV. > > If you have a 100 Hz signal you would say that the noise voltage is 10 > nV (on a 50 ohm resistor with a 100 Hz BW) > > Would you say 10 nV/sqrt(100Hz) ? (I don't think so) > > It seems to me that the notation of 1nV/sqrt(1Hz) is really just a > reminder that when calculating the noise voltage that the noise > voltage goes up by the square root of the Bandwidth, and is not really > relevant other than for the reminder. > > Agree?You seem to have misinterpreted something you read. Instead, read http://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise It will dispel some of the half truths that plague you. Jerry -- Engineering is the art of making what you want from things you can get.

Reply by ●September 7, 20112011-09-07

On Sep 7, 10:29�pm, dvsarwate <dvsarw...@yahoo.com> wrote:> On Sep 7, 9:43�pm, brent <buleg...@columbus.rr.com> wrote: > > > > > > > > > > > I have been pondering the notation for noise voltage. �The noise > > voltage across a 50 ohm resistor is expressed as 1nV/sqrt(1Hz) > > > As I ponder this it seems to me that one is concerned about the noise > > voltage period. �For instance, if you have a 1Hz BW signal you would > > say the noise voltage on a 50 ohm resistor is 1nV. > > > If you have a 100 Hz signal you would say that the noise voltage is 10 > > nV (on a 50 ohm resistor with a 100 Hz BW) > > > Would you say 10 nV/sqrt(100Hz) ? (I don't think so) > > > It seems to me that the notation of 1nV/sqrt(1Hz) is really just a > > reminder that when calculating the noise voltage that the noise > > voltage goes up by the square root of the Bandwidth, and is not really > > relevant other than for the reminder. > > > Agree? > > No.I love Usenet!

Reply by ●September 7, 20112011-09-07

On Sep 7, 10:52�pm, Jerry Avins <j...@ieee.org> wrote:> On 9/7/2011 9:43 PM, brent wrote: > > > I have been pondering the notation for noise voltage. �The noise > > voltage across a 50 ohm resistor is expressed as 1nV/sqrt(1Hz) > > Did you just make that up, or did you read it somewhere? > > > As I ponder this it seems to me that one is concerned about the noise > > voltage period. > > What do you call a voltage period? > > > � � � � � � � � For instance, if you have a 1Hz BW signal you would > > say the noise voltage on a 50 ohm resistor is 1nV. > > > If you have a 100 Hz signal you would say that the noise voltage is 10 > > nV (on a 50 ohm resistor with a 100 Hz BW) > > > Would you say 10 nV/sqrt(100Hz) ? (I don't think so) > > > It seems to me that the notation of 1nV/sqrt(1Hz) is really just a > > reminder that when calculating the noise voltage that the noise > > voltage goes up by the square root of the Bandwidth, and is not really > > relevant other than for the reminder. > > > Agree? > > You seem to have misinterpreted something you read. Instead, readhttp://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noiseIt will > dispel some of the half truths that plague you. > > Jerry > -- > Engineering is the art of making what you want from things you can get.Jerry, It is the notation in this very article (and in op amp data sheets) that is prompting my questions. For example, In the article they state that the noise voltage for a 1K resistor is 4.07nV/sqrt(1Hz).

Reply by ●September 8, 20112011-09-08

On 9/7/2011 10:58 PM, brent wrote:> On Sep 7, 10:52 pm, Jerry Avins<j...@ieee.org> wrote: >> On 9/7/2011 9:43 PM, brent wrote: >> >>> I have been pondering the notation for noise voltage. The noise >>> voltage across a 50 ohm resistor is expressed as 1nV/sqrt(1Hz) >> >> Did you just make that up, or did you read it somewhere? >> >>> As I ponder this it seems to me that one is concerned about the noise >>> voltage period. >> >> What do you call a voltage period? >> >>> For instance, if you have a 1Hz BW signal you would >>> say the noise voltage on a 50 ohm resistor is 1nV. >> >>> If you have a 100 Hz signal you would say that the noise voltage is 10 >>> nV (on a 50 ohm resistor with a 100 Hz BW) >> >>> Would you say 10 nV/sqrt(100Hz) ? (I don't think so) >> >>> It seems to me that the notation of 1nV/sqrt(1Hz) is really just a >>> reminder that when calculating the noise voltage that the noise >>> voltage goes up by the square root of the Bandwidth, and is not really >>> relevant other than for the reminder. >> >>> Agree? >> >> You seem to have misinterpreted something you read. Instead, readhttp://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noiseIt will >> dispel some of the half truths that plague you. >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get. > > Jerry, > > It is the notation in this very article (and in op amp data sheets) > that is prompting my questions. > > For example, In the article they state that the noise voltage for a 1K > resistor is 4.07nV/sqrt(1Hz).No they don't. They specifically state that that the noise voltage depends on temperature. The noise is statistical. The variance -- noise power -- depends on resistance and temperature. The measured voltage is determined by standard deviation, hence the square root. Jerry -- Engineering is the art of making what you want from things you can get.

Reply by ●September 8, 20112011-09-08

On Sep 7, 10:55�pm, brent <buleg...@columbus.rr.com> sarcastically commented: Brent2> I love Usenet! when I responded "No" to his query Brent1> Agree? following a series of mis-statements and half-truths. What answer other than Yes or No is there to the question asked? If you don't like the answer, and would have preferred the response Yes, too bad. Other responses such as Jerry Avins's more loquacious Jerry> You seem to have misinterpreted something you Jerry> read. Instead, read http://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise Jerry> It will dispel some of the half truths that plague you. indicate that nobody agrees with what Brent said in his original post. Dilip Sarwate

Reply by ●September 8, 20112011-09-08

On Sep 8, 7:52�am, dvsarwate <dvsarw...@yahoo.com> wrote:> On Sep 7, 10:55�pm, brent <buleg...@columbus.rr.com> > sarcastically commented: > > Brent2> I love Usenet! > > when I responded "No" to his query > > Brent1> �Agree? > > following a series of mis-statements and half-truths. > > What answer other than Yes or No is there to the question > asked? �If you don't like the answer, and would have > preferred the response Yes, too bad. �Other responses > such as Jerry Avins's more loquacious > > Jerry> �You seem to have misinterpreted something you > Jerry> �read. Instead, readhttp://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise > Jerry> �It will dispel some of the half truths that plague you. > > indicate that nobody agrees with what Brent said in > his original post. > > Dilip SarwateI don't know why you are explaining so much here. Your one word answer was exactly what I needed, which is why I said I love usenet , because your two letter answer provided tremendous insight into my question about this. Please chime in with as few (but insightful) letters as possible in the future. The fewer the letters the more helpful! Thanks!!!!

Reply by ●September 9, 20112011-09-09