A collection of monographs on high accuracy electronics

I've down-loaded it. It reminds me a lot of "Coaxial AC Bridges" by Kibble and Rayner ISBN 0-85274-389-0, which the author should find flattering. Kibble is also the Kibble in the Kibble Bridge.

Thanks! Ed

Yes, thanks to whoever posted this; very interesting indeed.

I have an issue with his definition of resistor noise power as the product of open-circuit noise voltage and short-circuit current. That makes no sense.

There's more than that, probably, but that just jumped out at me.

Jeroen Belleman

It’s four times too high, for a start.

Cheers

Phil Hobbs

"It is shown elsewhere [1] that the noise power is four times the heat energy which would flow down the conductors from a warm source resistor to a matching cold resistor."

Which, if true, would solve all our energy problems, except that thermodynamic systems would all be unstable.

The thermal noise power produced by a resistor into a matched load is kT per hertz.

Cheers

Phil Hobbs

Sure, which is what he states. By mentioning a hot and cold resistor he makes it clear that net energy flow is from hot to cold, and that the T refers to the hot source.

If you connect two resistors, the noise voltages create an equivalent thermal conductivity. I did the math once and I recall that any reasonable real wires would conduct a lot more heat.

And in real life, capacitance will kill the bandwidth and the heat transfer.

But apparently he says that it's four times larger than that.

I'm not making a microsoft account just to download the PDF, so if you want to discuss it further, you could email it to me.

Cheers

Phil Hobbs

Bill was kind enough to send me a copy (thanks again, Bill), and right there on P. 374, the author says,

Pn = 4kTB

which is a factor of four too high.

Twenty years ago I posted a brief derivation of the Johnson noise formula in the thread "thermal noise in resistors - Baffled!", as follows (with a couple of typos fixed).

Cheers

Phil Hobbs

And again the following year, with more discussion...this qualifies as a well-aged FAQ. ;)

Cheers

Phil Hobbs

That link doesn’t work for me, is there some other way to access it please?

No it isn't. He is calculating the thermal noise power dissipated in an unloaded resistor - something (or at least the related noise voltage) which is actually required in the design process of a transducer/amplifier low S/N system. No engineer outwith some RF/microwave areas (such are specifing antenna noise temperature) is remotely interested in your definition of noise power as the maximum power which can be extracted from a thermal source (ie by a conjugate source match). The vast majority of engineers (if asked to specify resistor noise power) would present exactly the same equation as Daykin, because they are interested in noise voltage (or current) only.

What does that mean? Do unconnected resistors get hot?

A box of resistors could start a fire!

John, I’m sorry that your friend is dying. The fact that it comes to us all doesn’t make it any easier to take.

I’m reading his stuff, so far with interest, and have zero interest in rubbishing it, or him.

You said yourself that it was unfinished, which means in part that he didn’t get the chance to check the final version for errors.

This one error doesn’t mean that it’s worthless, just unfinished.

My first edition contained 107 errors that I know about, which fortunately I was able to fix in later printings. So believe me, I understand the problem.

Cheers

Phil Hobbs

No. They certainly don't get warmer than their enviroment, though they do interact with it.

Obviously not. John Larkin's sense of humour is depressingly pathetic.

This appears to be almost the same document but has 457 rather than 463 pages.

And why would that occur. In thermal equilibrium there is no net transfer of energy either from or to the resistor (when averaged over any time interval of interest appropriate to the bandwidth of current electronic circuits).

The so called resistor thermal "available noise power" KTB implies there is a net power delivery from a source to a load. In the case of maximum transfer the source must dissipate within itself exactly the same as it delivers to the load (due to having the same resistance). However if the so called load is at the same temperature as the source it also delivers KTB to the source and dissipates KTB within its own resistance. Thus there is no net transfer of energy between the two resistors in thermal equilibrium. If one is at a lower temperature than the other there will be a net transfer of energy, but this will be completely dwarfed in any practical system by the energy transferred due to thermal conductivity between the two resistors.

So the power dissipated in a system of two equal value resistors is 4KTB. But this also holds if the two resistors have different values, including the situation where one of the resistors is a short or open circuit (i.e. leaving a single open or short circuit resistor). So it is entirely reasonable to state (as many engineers do) that the thermal noise power of a resistor is 4kTB.