On Tue, 2 Jun 2009 19:33:47 -0700 (PDT), ggherold@gmail.com wrote:>On Jun 2, 12:26�pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Tue, 02 Jun 2009 18:03:42 +1000, F Murtz <hagg...@hotmail.com> >> wrote: >> >> >Eric Gisse wrote: >> >> On Jun 1, 4:15 pm, GreenXenon <glucege...@gmail.com> wrote: >> >>> Hi: >> >> >>> What is the smallest physically-possible voltage that can be detected >> >>> or processed given the state of today's technology? >> >> >>> Thanks >> >> >> Oh my god please fuck off from sci.physics. We do not want you. >> >Is there any one in this group with the necessary scholastic >> >qualifications to diagnose the reason this poster asks such esoteric >> >questions >> >> He seems interested in the issues but confused about physical units. >> >> I suppose I should get on with writing my book, to make all this stuff >> plain. >> >> John > >John, Are you really writing a book. You can sign me up for a >copy. > >And if you want to measure a small voltage (difference) you need to >also specify how long you are willing to wait for measurement. Give >me a billion years and I can do a lot of averaging. > >George HeroldIf you can turn the source on and off, and can do the lock-in thing, you could measure a picovolt to decent accuracy in an afternoon. John
What is the smallest physically-possible voltage that can be detected or processed given the state of today's technology?
Started by ●June 1, 2009
Reply by ●June 3, 20092009-06-03
Reply by ●June 3, 20092009-06-03
In comp.dsp John Larkin <jjlarkin@highnotlandthistechnologypart.com> wrote: < Femtovolts, with an FM receiver? Good ones need microvolt or so. A 3 < dB noise figure, optimistic for a radio, is ballpark 1 nV RMS noise < per root Hz, and an FM radio has a couple of hundred KHz bandwidth. How about traditional satellite TV? As I remember, it is about six watts per channel. If the signal covers most of the continental US, a 10m dish has about 1/(500000)**2 the area of the US, so about 6W/2.5e11 or about 2.4e-11W At 75 ohms that is about 40uV. I would expect that to be a lot less than FM radio with 100kW transmitters. On the other hand, my cable modem has about +16dBm input at 75 ohms. About 1.7V, maybe enough for a small light bulb. (I believe that is only for the specific signal it is receiving, not counting the hundreds of other cable channels.) -- glen
Reply by ●June 3, 20092009-06-03
On Jun 2, 10:33�pm, ggher...@gmail.com wrote:> On Jun 2, 12:26�pm, John Larkin > > > > > > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > > On Tue, 02 Jun 2009 18:03:42 +1000, F Murtz <hagg...@hotmail.com> > > wrote: > > > >Eric Gisse wrote: > > >> On Jun 1, 4:15 pm, GreenXenon <glucege...@gmail.com> wrote: > > >>> Hi: > > > >>> What is the smallest physically-possible voltage that can be detected > > >>> or processed given the state of today's technology? > > > >>> Thanks > > > >> Oh my god please fuck off from sci.physics. We do not want you. > > >Is there any one in this group with the necessary scholastic > > >qualifications to diagnose the reason this poster asks such esoteric > > >questions > > > He seems interested in the issues but confused about physical units. > > > I suppose I should get on with writing my book, to make all this stuff > > plain. > > > John > > John, �Are you really writing a book. �You can sign me up for a > copy. > > And if you want to measure a small voltage (difference) you need to > also specify how long you are willing to wait for measurement. �Give > me a billion years and I can do a lot of averaging. > > George Herold- Hide quoted text - > > - Show quoted text -opps 'wait for "the" measurement. George
Reply by ●June 3, 20092009-06-03
On Jun 3, 5:18�pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Tue, 2 Jun 2009 19:33:47 -0700 (PDT), ggher...@gmail.com wrote: > >On Jun 2, 12:26�pm, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> On Tue, 02 Jun 2009 18:03:42 +1000, F Murtz <hagg...@hotmail.com> > >> wrote: > > >> >Eric Gisse wrote: > >> >> On Jun 1, 4:15 pm, GreenXenon <glucege...@gmail.com> wrote: > >> >>> Hi: > > >> >>> What is the smallest physically-possible voltage that can be detected > >> >>> or processed given the state of today's technology? > > >> >>> Thanks > > >> >> Oh my god please fuck off from sci.physics. We do not want you. > >> >Is there any one in this group with the necessary scholastic > >> >qualifications to diagnose the reason this poster asks such esoteric > >> >questions > > >> He seems interested in the issues but confused about physical units. > > >> I suppose I should get on with writing my book, to make all this stuff > >> plain. > > >> John > > >John, �Are you really writing a book. �You can sign me up for a > >copy. > > >And if you want to measure a small voltage (difference) you need to > >also specify how long you are willing to wait for measurement. �Give > >me a billion years and I can do a lot of averaging. > > >George Herold > > If you can turn the source on and off, and can do the lock-in thing, > you could measure a picovolt to decent accuracy in an afternoon. > > John- Hide quoted text - > > - Show quoted text -Hmm, at 1nV/rtHz it's going to take me 10^6 seconds to get down to 1 pV. But that's a straight noise measurement. I guess if I've got a 1pV signal and can add that on and off to 1nV of noise I can build up to 1 SNR in 2000 seconds. If the measurement period gets longer than a day you have to start to really worry about all sorts of strange effects. (Have you every read R.V. Jones, Instruments and Experiences (1988). Some great tales for instument builders. I'm also reminded of a recent report, on old data, (in phyiscs today?) about nuclear decays that showed a period of one year. George Herold
Reply by ●June 4, 20092009-06-04
On Wed, 3 Jun 2009 19:17:24 -0700 (PDT), ggherold@gmail.com wrote:>On Jun 3, 5:18�pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Tue, 2 Jun 2009 19:33:47 -0700 (PDT), ggher...@gmail.com wrote: >> >On Jun 2, 12:26�pm, John Larkin >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >> On Tue, 02 Jun 2009 18:03:42 +1000, F Murtz <hagg...@hotmail.com> >> >> wrote: >> >> >> >Eric Gisse wrote: >> >> >> On Jun 1, 4:15 pm, GreenXenon <glucege...@gmail.com> wrote: >> >> >>> Hi: >> >> >> >>> What is the smallest physically-possible voltage that can be detected >> >> >>> or processed given the state of today's technology? >> >> >> >>> Thanks >> >> >> >> Oh my god please fuck off from sci.physics. We do not want you. >> >> >Is there any one in this group with the necessary scholastic >> >> >qualifications to diagnose the reason this poster asks such esoteric >> >> >questions >> >> >> He seems interested in the issues but confused about physical units. >> >> >> I suppose I should get on with writing my book, to make all this stuff >> >> plain. >> >> >> John >> >> >John, �Are you really writing a book. �You can sign me up for a >> >copy. >> >> >And if you want to measure a small voltage (difference) you need to >> >also specify how long you are willing to wait for measurement. �Give >> >me a billion years and I can do a lot of averaging. >> >> >George Herold >> >> If you can turn the source on and off, and can do the lock-in thing, >> you could measure a picovolt to decent accuracy in an afternoon. >> >> John- Hide quoted text - >> >> - Show quoted text - > >Hmm, at 1nV/rtHz it's going to take me 10^6 seconds to get down to 1 >pV. But that's a straight noise measurement. I guess if I've got a >1pV signal and can add that on and off to 1nV of noise I can build up >to 1 SNR in 2000 seconds.I think that works. The measurement bandwidth is 1/2000 Hz or something. OK, maybe a week or so. Somebody does sell a voltmeter that resolves 200 pV, slowly I assume.> >If the measurement period gets longer than a day you have to start to >really worry about all sorts of strange effects. (Have you every read >R.V. Jones, Instruments and Experiences (1988). Some great tales for >instument builders.I'll try to find that.> >I'm also reminded of a recent report, on old data, (in phyiscs today?) >about nuclear decays that showed a period of one year.Yup, there are suggestions that certain isotope decays are affected by the distance to the sun or something. Strange. John
Reply by ●June 4, 20092009-06-04
glen herrmannsfeldt wrote:> > In comp.dsp John Larkin <jjlarkin@highnotlandthistechnologypart.com> wrote: > > < Femtovolts, with an FM receiver? Good ones need microvolt or so. A 3 > < dB noise figure, optimistic for a radio, is ballpark 1 nV RMS noise > < per root Hz, and an FM radio has a couple of hundred KHz bandwidth. > > How about traditional satellite TV? As I remember, it is about six > watts per channel. If the signal covers most of the continental US, > a 10m dish has about 1/(500000)**2 the area of the US, so about > 6W/2.5e11 or about 2.4e-11W At 75 ohms that is about 40uV.Try that without the feed horn and dish to supply a fair amount of gain. The early 'Galaxy' birds were 10 watts per transponder. -- You can't have a sense of humor, if you have no sense!
Reply by ●June 4, 20092009-06-04
On Jun 3, 11:04�pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Wed, 3 Jun 2009 19:17:24 -0700 (PDT), ggher...@gmail.com wrote: > >On Jun 3, 5:18�pm, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> On Tue, 2 Jun 2009 19:33:47 -0700 (PDT), ggher...@gmail.com wrote: > >> >On Jun 2, 12:26�pm, John Larkin > >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> >> On Tue, 02 Jun 2009 18:03:42 +1000, F Murtz <hagg...@hotmail.com> > >> >> wrote: > > >> >> >Eric Gisse wrote: > >> >> >> On Jun 1, 4:15 pm, GreenXenon <glucege...@gmail.com> wrote: > >> >> >>> Hi: > > >> >> >>> What is the smallest physically-possible voltage that can be detected > >> >> >>> or processed given the state of today's technology? > > >> >> >>> Thanks > > >> >> >> Oh my god please fuck off from sci.physics. We do not want you. > >> >> >Is there any one in this group with the necessary scholastic > >> >> >qualifications to diagnose the reason this poster asks such esoteric > >> >> >questions > > >> >> He seems interested in the issues but confused about physical units. > > >> >> I suppose I should get on with writing my book, to make all this stuff > >> >> plain. > > >> >> John > > >> >John, �Are you really writing a book. �You can sign me up for a > >> >copy. > > >> >And if you want to measure a small voltage (difference) you need to > >> >also specify how long you are willing to wait for measurement. �Give > >> >me a billion years and I can do a lot of averaging. > > >> >George Herold > > >> If you can turn the source on and off, and can do the lock-in thing, > >> you could measure a picovolt to decent accuracy in an afternoon. > > >> John- Hide quoted text - > > >> - Show quoted text - > > >Hmm, �at 1nV/rtHz it's going to take me 10^6 seconds to get down to 1 > >pV. �But that's a straight noise measurement. �I guess if I've got a > >1pV signal and can add that on and off to 1nV of noise I can build up > >to 1 SNR in 2000 seconds. > > I think that works. The measurement bandwidth is 1/2000 Hz or > something. OK, maybe a week or so. Somebody does sell a voltmeter that > resolves 200 pV, slowly I assume. > > > > >If the measurement period gets longer than a day you have to start to > >really worry about all sorts of strange effects. �(Have you every read > >R.V. Jones, Instruments and Experiences (1988). �Some great tales for > >instument builders. > > I'll try to find that. > > > > >I'm also reminded of a recent report, on old data, (in phyiscs today?) > >about nuclear decays that showed a period of one year. > > Yup, there are suggestions that certain isotope decays are affected by > the distance to the sun or something. Strange. > > John- Hide quoted text - > > - Show quoted text -Try a university library for the book. I borrowed a copy from a colleague. I've been watching the used book sites on and off and it's always at least $200.00 (sigh) My guess on the distance from the sun decay rates is that they didn't understand all the systematic errors in their apparatus. Not that I think I could have done better. Making measurements that last years has got to be hard. I do hope someone is trying to repeat it though, except for neutrino mass there hasn�t been any new (experimental) particle physics in a while. George H.
Reply by ●June 4, 20092009-06-04
On Jun 3, 5:09�pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Tue, 02 Jun 2009 18:40:51 -0700, ItsASecretDummy > > > > <secretasian...@thebarattheendoftheuniverse.org> wrote: > >On Mon, 1 Jun 2009 22:00:07 -0700, "Eric Jacobsen" > ><eric.jacob...@ieee.org> wrote: > > >>"Michael A. Terrell" <mike.terr...@earthlink.net> wrote in message > >>news:CMudnRFLId9xOrnXnZ2dnUVZ_qCdnZ2d@earthlink.com... > > >>> rickman wrote: > > >>>> On Jun 1, 10:33 pm, ItsASecretDummy > >>>> <secretasian...@thebarattheendoftheuniverse.org> wrote: > >>>> > On Mon, 01 Jun 2009 17:40:20 -0700, John Larkin > > >>>> > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > > >>>> > >Single-electron transistors can sense, well, single electrons. > > >>>> > >John > > >>>> > � PMTs can be good enough to detect single photon events. > > >>>> Hmmm... �I have a $35 digital multimeter that can measure exactly 0 > >>>> volts! > > >>> � �No, it can't. �It can display zero, even with some voltage at the > >>> input. �The issues is the resolution of the meter. �Even with the probes > >>> shorted, you will have some Johnson noise which is generated by the > >>> resistors in the input circuitry, if the meter is above absolute zero > >>> degrees. That voltage is too low to be displayed, but it is still there. > > >>> -- > >>> You can't have a sense of humor, if you have no sense! > > >>Yeah, but when it's exactly zero volts, that what the $35 multimeter will > >>display, > > >] �Not if it is turned on it wont. > > >> so he wasn't incorrect. > > > �Oh yes he was, and so is most of the other responses to him. > > > �If the meter is off, there will be no display. �If it is on, it will > >not be very likely to read zero volts when probing a bare piece of metal > >or shorting the leads. > > > �Like a scale that has been zeroed, one will see drift above and below > >the zero line if the scale can resolve to tenths of a gram. �It will also > >drift as the internal electronics heats up. Not so much with a meter as > >with scale electronics, for some reason. > > > �So if the meter has more than 2 digits behind the decimal point, one > >will likely see errant values pop in and out. > > Fluke 75, shorted leads, VDC range: steady � .000 > > Fluke 87, ditto: �steady �0.000 > > AlwaysWrong. > > JohnAre you going to return these meters for repair? Rick
Reply by ●June 4, 20092009-06-04
On Thu, 4 Jun 2009 12:03:11 -0700 (PDT), rickman <gnuarm@gmail.com> wrote:>On Jun 3, 5:09�pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Tue, 02 Jun 2009 18:40:51 -0700, ItsASecretDummy >> >> >> >> <secretasian...@thebarattheendoftheuniverse.org> wrote: >> >On Mon, 1 Jun 2009 22:00:07 -0700, "Eric Jacobsen" >> ><eric.jacob...@ieee.org> wrote: >> >> >>"Michael A. Terrell" <mike.terr...@earthlink.net> wrote in message >> >>news:CMudnRFLId9xOrnXnZ2dnUVZ_qCdnZ2d@earthlink.com... >> >> >>> rickman wrote: >> >> >>>> On Jun 1, 10:33 pm, ItsASecretDummy >> >>>> <secretasian...@thebarattheendoftheuniverse.org> wrote: >> >>>> > On Mon, 01 Jun 2009 17:40:20 -0700, John Larkin >> >> >>>> > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >> >>>> > >Single-electron transistors can sense, well, single electrons. >> >> >>>> > >John >> >> >>>> > � PMTs can be good enough to detect single photon events. >> >> >>>> Hmmm... �I have a $35 digital multimeter that can measure exactly 0 >> >>>> volts! >> >> >>> � �No, it can't. �It can display zero, even with some voltage at the >> >>> input. �The issues is the resolution of the meter. �Even with the probes >> >>> shorted, you will have some Johnson noise which is generated by the >> >>> resistors in the input circuitry, if the meter is above absolute zero >> >>> degrees. That voltage is too low to be displayed, but it is still there. >> >> >>> -- >> >>> You can't have a sense of humor, if you have no sense! >> >> >>Yeah, but when it's exactly zero volts, that what the $35 multimeter will >> >>display, >> >> >] �Not if it is turned on it wont. >> >> >> so he wasn't incorrect. >> >> > �Oh yes he was, and so is most of the other responses to him. >> >> > �If the meter is off, there will be no display. �If it is on, it will >> >not be very likely to read zero volts when probing a bare piece of metal >> >or shorting the leads. >> >> > �Like a scale that has been zeroed, one will see drift above and below >> >the zero line if the scale can resolve to tenths of a gram. �It will also >> >drift as the internal electronics heats up. Not so much with a meter as >> >with scale electronics, for some reason. >> >> > �So if the meter has more than 2 digits behind the decimal point, one >> >will likely see errant values pop in and out. >> >> Fluke 75, shorted leads, VDC range: steady � .000 >> >> Fluke 87, ditto: �steady �0.000 >> >> AlwaysWrong. >> >> John > >Are you going to return these meters for repair? > >RickWe do have an Agilent 34401A benchtop DVM. It has a VF display that kicks huge noise spikes out the front-panel connectors. So on the low AC ranges, it's pretty much measuring its own spikes. So they boogered the firmware so that, just above that noise floor, the displayed value drops to exactly zero. John
Reply by ●June 4, 20092009-06-04
