Re: [time-nuts] Low noise powersupplies
David, Did you ever get an answer? Original Post: Date: Fri, 08 Aug 2014 00:10:58 +1000 From: David Hooke dho...@gmail.com To: bruce-cpdlzquo8hwavxtiumw...@public.gmane.org Subject: Re: [time-nuts] Low noise powersupplies Message-ID: 53e388f2@gmail.com Such as? david On 7/08/2014 9:30 PM, bruce-cpdlzquo8hwavxtiumw...@public.gmane.org wrote: I have a couple of these. however their noise spectral density tends to rise precipitously below 1Hz or so. There are regulators with significantly lower flicker noise. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
Am 08.08.2014 um 02:13 schrieb Alexander Pummer: people who designing low noise PLLs solved that problem a while ego go to Charles Wenzels circuit collections he made a very low noise from DC to a few hundred kHz amplifier just to amplify the phase noise, here is: http://www.techlib.com/files/lowamp.pdf You can also try my preamp: http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf with some preliminary results on batteries: http://www.hoffmann-hochfrequenz.de/downloads/Noise_Behaviour_Of_Chemical_Batteries_V1.0.pdf (very preliminary, could not get the 89441A to do a multi-decade FFT from 0.1Hz to 1 MHz, but figured out how to control it via the network over tcp/ip. Must take multiple measurements, paste it together and plot it with gnuplot, takes soo much time to write...) Since NiCds seem to max out the 220pV/sqrt Hz, I'm also working on a stereo version of the preamp so I can use the cross correlation feature to get another 25 dB. But even now the thermal noise of 60 Ohm (1nV/sqrtHZ) is consistently in the upper half of the plots :-) It will have all controls settable via tcp/ip and bistable relays a BeagleBoneBlack. There a too many possible errors if I try to do it by hand. Also, my preamp has 1 dB droop at 1 MHz, that's not really flat for my taste. regards, Gerhard (holidays in Bretagne, it rains, I wished I had the 89441 here...) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
An application note (http://cds.linear.com/docs/en/application-note/an124f.pdf) from Jim Williams and the related video (https://www.youtube.com/watch?v=Ta1ZuZTHYXA) may be informative. Edésio On Thu, Aug 07, 2014 at 01:41:32PM -0700, Chris Albertson wrote: Just practical question.. How would one measure noise at this level? If I were evaluate this what would I need? My scope lacks a nV/dev setting so is there some way to tell the difference between this and an LM317? Seriously, what kind of instrumentation would I need before I could measure an improvement over my standard LM317 On Wed, Aug 6, 2014 at 11:38 PM, Ole Petter Ronningen olep...@gmail.com wrote: Hello, all I thought it may be of interest to some of the members of this list that TI is selling evaluation modules for some ultra low noise regulators for $20 in their estore, shipping world wide included. The specs looks pretty decent to me, and I've ordered up a couple of boards to use as clean up boxes for my bench-supplies, to use on noise-sensitive projects. 1.4-30v output TPS7A4701EVM-094 3.5µVRMS (10Hz, 100KHz) 25 nV/???Hz (10Hz, 1MHz) Maximum Output Current of 1A +-15v version TPS7A30-49EVM-567: 15v rail: Noise: 12.7µVRMS (20Hz to 20kHz) 15.4µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ??? 52dB (10Hz to 400kHz) Maximum Output Current: 150mA -15v rail: Noise: 14µVRMS (20Hz to 20kHz) 15.1µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ??? 55dB (10Hz to 700kHz) Maximum Output Current: 200mA Ole ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
An application note (http://cds.linear.com/docs/en/application-note/an124f.pdf) from Jim Williams and the related video (https://www.youtube.com/watch?v=Ta1ZuZTHYXA) may be informative. Edésio On Thu, Aug 07, 2014 at 01:41:32PM -0700, Chris Albertson wrote: Just practical question.. How would one measure noise at this level? If I were evaluate this what would I need? My scope lacks a nV/dev setting so is there some way to tell the difference between this and an LM317? Seriously, what kind of instrumentation would I need before I could measure an improvement over my standard LM317 On Wed, Aug 6, 2014 at 11:38 PM, Ole Petter Ronningen olep...@gmail.com wrote: Hello, all I thought it may be of interest to some of the members of this list that TI is selling evaluation modules for some ultra low noise regulators for $20 in their estore, shipping world wide included. The specs looks pretty decent to me, and I've ordered up a couple of boards to use as clean up boxes for my bench-supplies, to use on noise-sensitive projects. 1.4-30v output TPS7A4701EVM-094 3.5µVRMS (10Hz, 100KHz) 25 nV/???Hz (10Hz, 1MHz) Maximum Output Current of 1A +-15v version TPS7A30-49EVM-567: 15v rail: Noise: 12.7µVRMS (20Hz to 20kHz) 15.4µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ??? 52dB (10Hz to 400kHz) Maximum Output Current: 150mA -15v rail: Noise: 14µVRMS (20Hz to 20kHz) 15.1µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ??? 55dB (10Hz to 700kHz) Maximum Output Current: 200mA Ole ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
Ole, Thanks for bringing it to our attention. For those that like to click instead of search: http://www.ti.com/tool/TPS7A4701EVM-094 http://www.ti.com/lit/ug/slvu741a/slvu741a.pdf http://www.ti.com/product/tps7a4701 http://www.ti.com/lit/ds/symlink/tps7a4701.pdf /tvb - Original Message - From: Ole Petter Ronningen olep...@gmail.com To: time-nuts@febo.com Sent: Wednesday, August 06, 2014 11:38 PM Subject: [time-nuts] Low noise powersupplies Hello, all I thought it may be of interest to some of the members of this list that TI is selling evaluation modules for some ultra low noise regulators for $20 in their estore, shipping world wide included. The specs looks pretty decent to me, and I've ordered up a couple of boards to use as clean up boxes for my bench-supplies, to use on noise-sensitive projects. 1.4-30v output TPS7A4701EVM-094 3.5µVRMS (10Hz, 100KHz) 25 nV/√Hz (10Hz, 1MHz) Maximum Output Current of 1A +-15v version TPS7A30-49EVM-567: 15v rail: Noise: 12.7µVRMS (20Hz to 20kHz) 15.4µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ≥ 52dB (10Hz to 400kHz) Maximum Output Current: 150mA -15v rail: Noise: 14µVRMS (20Hz to 20kHz) 15.1µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ≥ 55dB (10Hz to 700kHz) Maximum Output Current: 200mA Ole ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
I have a couple of these. however their noise spectral density tends to rise precipitously below 1Hz or so. There are regulators with significantly lower flicker noise. Bruce On August 7, 2014 at 6:35 AM Tom Van Baak t...@leapsecond.com wrote: Ole, Thanks for bringing it to our attention. For those that like to click instead of search: http://www.ti.com/tool/TPS7A4701EVM-094 http://www.ti.com/lit/ug/slvu741a/slvu741a.pdf http://www.ti.com/product/tps7a4701 http://www.ti.com/lit/ds/symlink/tps7a4701.pdf /tvb - Original Message - From: Ole Petter Ronningen olep...@gmail.com To: time-nuts@febo.com Sent: Wednesday, August 06, 2014 11:38 PM Subject: [time-nuts] Low noise powersupplies Hello, all I thought it may be of interest to some of the members of this list that TI is selling evaluation modules for some ultra low noise regulators for $20 in their estore, shipping world wide included. The specs looks pretty decent to me, and I've ordered up a couple of boards to use as clean up boxes for my bench-supplies, to use on noise-sensitive projects. 1.4-30v output TPS7A4701EVM-094 3.5µVRMS (10Hz, 100KHz) 25 nV/√Hz (10Hz, 1MHz) Maximum Output Current of 1A +-15v version TPS7A30-49EVM-567: 15v rail: Noise: 12.7µVRMS (20Hz to 20kHz) 15.4µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ≥ 52dB (10Hz to 400kHz) Maximum Output Current: 150mA -15v rail: Noise: 14µVRMS (20Hz to 20kHz) 15.1µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ≥ 55dB (10Hz to 700kHz) Maximum Output Current: 200mA Ole ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
Such as? david On 7/08/2014 9:30 PM, bruce-cpdlzquo8hwavxtiumw...@public.gmane.org wrote: I have a couple of these. however their noise spectral density tends to rise precipitously below 1Hz or so. There are regulators with significantly lower flicker noise. Bruce On August 7, 2014 at 6:35 AM Tom Van Baak t...@leapsecond.com wrote: Ole, Thanks for bringing it to our attention. For those that like to click instead of search: http://www.ti.com/tool/TPS7A4701EVM-094 http://www.ti.com/lit/ug/slvu741a/slvu741a.pdf http://www.ti.com/product/tps7a4701 http://www.ti.com/lit/ds/symlink/tps7a4701.pdf /tvb - Original Message - From: Ole Petter Ronningen olep...@gmail.com To: time-nuts@febo.com Sent: Wednesday, August 06, 2014 11:38 PM Subject: [time-nuts] Low noise powersupplies Hello, all I thought it may be of interest to some of the members of this list that TI is selling evaluation modules for some ultra low noise regulators for $20 in their estore, shipping world wide included. The specs looks pretty decent to me, and I've ordered up a couple of boards to use as clean up boxes for my bench-supplies, to use on noise-sensitive projects. 1.4-30v output TPS7A4701EVM-094 3.5µVRMS (10Hz, 100KHz) 25 nV/√Hz (10Hz, 1MHz) Maximum Output Current of 1A +-15v version TPS7A30-49EVM-567: 15v rail: Noise: 12.7µVRMS (20Hz to 20kHz) 15.4µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ≥ 52dB (10Hz to 400kHz) Maximum Output Current: 150mA -15v rail: Noise: 14µVRMS (20Hz to 20kHz) 15.1µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ≥ 55dB (10Hz to 700kHz) Maximum Output Current: 200mA Ole ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
Just practical question.. How would one measure noise at this level? If I were evaluate this what would I need? My scope lacks a nV/dev setting so is there some way to tell the difference between this and an LM317? Seriously, what kind of instrumentation would I need before I could measure an improvement over my standard LM317 On Wed, Aug 6, 2014 at 11:38 PM, Ole Petter Ronningen olep...@gmail.com wrote: Hello, all I thought it may be of interest to some of the members of this list that TI is selling evaluation modules for some ultra low noise regulators for $20 in their estore, shipping world wide included. The specs looks pretty decent to me, and I've ordered up a couple of boards to use as clean up boxes for my bench-supplies, to use on noise-sensitive projects. 1.4-30v output TPS7A4701EVM-094 3.5µVRMS (10Hz, 100KHz) 25 nV/√Hz (10Hz, 1MHz) Maximum Output Current of 1A +-15v version TPS7A30-49EVM-567: 15v rail: Noise: 12.7µVRMS (20Hz to 20kHz) 15.4µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ≥ 52dB (10Hz to 400kHz) Maximum Output Current: 150mA -15v rail: Noise: 14µVRMS (20Hz to 20kHz) 15.1µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ≥ 55dB (10Hz to 700kHz) Maximum Output Current: 200mA Ole ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
to measure a power supply noise, better to say the noise spectrum, you would need a very large non polarized capacitor and spectrum analyzer, The input of the spectrum analyzer does not like DC, and has low impedance. Since spectrum analyzer's input impedance is usually 50 ohm, for to be able to see the noise at low frequency you need C = 1/( 2 x 3.14 x 50 ohm x f Hz ) capacitor, and you would need a DC level limiter to prevent blowing the input of the spectrum analyzer during the charge up of that capacitor. If you could get a hold of an old HP 1Meg to 50ohm buffer amplifier you would need much lover capacitance or if the buffer has AC input capability with low enough corner frequency like the Tektronix P6201 FET probe, you would not need any capacitor. And that would make your life much nicer since capacitors could generate noise to.. Charles Wenzel in his circuit collection files ha very nice good working noise reduction circuits. 73 Alex KJ6UHN On 8/7/2014 1:41 PM, Chris Albertson wrote: Just practical question.. How would one measure noise at this level? If I were evaluate this what would I need? My scope lacks a nV/dev setting so is there some way to tell the difference between this and an LM317? Seriously, what kind of instrumentation would I need before I could measure an improvement over my standard LM317 On Wed, Aug 6, 2014 at 11:38 PM, Ole Petter Ronningen olep...@gmail.com wrote: Hello, all I thought it may be of interest to some of the members of this list that TI is selling evaluation modules for some ultra low noise regulators for $20 in their estore, shipping world wide included. The specs looks pretty decent to me, and I've ordered up a couple of boards to use as clean up boxes for my bench-supplies, to use on noise-sensitive projects. 1.4-30v output TPS7A4701EVM-094 3.5µVRMS (10Hz, 100KHz) 25 nV/√Hz (10Hz, 1MHz) Maximum Output Current of 1A +-15v version TPS7A30-49EVM-567: 15v rail: Noise: 12.7µVRMS (20Hz to 20kHz) 15.4µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ≥ 52dB (10Hz to 400kHz) Maximum Output Current: 150mA -15v rail: Noise: 14µVRMS (20Hz to 20kHz) 15.1µVRMS (10Hz to 100kHz) Power-Supply Ripple Rejection: 72dB (120Hz) ≥ 55dB (10Hz to 700kHz) Maximum Output Current: 200mA Ole ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
What about a PC sound card? From: Alexander Pummer alex...@ieee.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, August 7, 2014 5:06 PM Subject: Re: [time-nuts] Low noise powersupplies to measure a power supply noise, better to say the noise spectrum, you would need a very large non polarized capacitor and spectrum analyzer, The input of the spectrum analyzer does not like DC, and has low impedance. Since spectrum analyzer's input impedance is usually 50 ohm, for to be able to see the noise at low frequency you need C = 1/( 2 x 3.14 x 50 ohm x f Hz ) capacitor, and you would need a DC level limiter to prevent blowing the input of the spectrum analyzer during the charge up of that capacitor. If you could get a hold of an old HP 1Meg to 50ohm buffer amplifier you would need much lover capacitance or if the buffer has AC input capability with low enough corner frequency like the Tektronix P6201 FET probe, you would not need any capacitor. And that would make your life much nicer since capacitors could generate noise to.. Charles Wenzel in his circuit collection files ha very nice good working noise reduction circuits. 73 Alex KJ6UHN ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
the PC sound card has limited bandwidth bellow 20Hz and above 20kHz, is nothing and also it is not so noise less like a spectrum analyzer which was made to analyze spectrum and the sound card self is in a relative noisy environment in the PC On 8/7/2014 3:09 PM, Bob Stewart wrote: What about a PC sound card? From: Alexander Pummer alex...@ieee.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, August 7, 2014 5:06 PM Subject: Re: [time-nuts] Low noise powersupplies to measure a power supply noise, better to say the noise spectrum, you would need a very large non polarized capacitor and spectrum analyzer, The input of the spectrum analyzer does not like DC, and has low impedance. Since spectrum analyzer's input impedance is usually 50 ohm, for to be able to see the noise at low frequency you need C = 1/( 2 x 3.14 x 50 ohm x f Hz ) capacitor, and you would need a DC level limiter to prevent blowing the input of the spectrum analyzer during the charge up of that capacitor. If you could get a hold of an old HP 1Meg to 50ohm buffer amplifier you would need much lover capacitance or if the buffer has AC input capability with low enough corner frequency like the Tektronix P6201 FET probe, you would not need any capacitor. And that would make your life much nicer since capacitors could generate noise to.. Charles Wenzel in his circuit collection files ha very nice good working noise reduction circuits. 73 Alex KJ6UHN ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
Hi A low noise chopper stabilized op amp can make a pretty good pre-amp to put in front of a low frequency spectrum analyzer. Something in the 20 to 30 db gain is adequate for most analyzers. That will get you down to a level that’s well below the noise floor on any OCXO I have ever seen. Here’s a way to look at it: The input resistors on the OCXO have KBT noise (they are real resistors). They also are in the “many thousands of ohms” range. If you short the EFC (zero noise in) you still have resistor voltage noise modulating the EFC. All you need to do is to get down to the KTB level in a few thousand ohm resistor. Yes 1/F noise does get into the mix. That’s why you want the chopper. Bob On Aug 7, 2014, at 6:32 PM, Alex Pummer a...@pcscons.com wrote: the PC sound card has limited bandwidth bellow 20Hz and above 20kHz, is nothing and also it is not so noise less like a spectrum analyzer which was made to analyze spectrum and the sound card self is in a relative noisy environment in the PC On 8/7/2014 3:09 PM, Bob Stewart wrote: What about a PC sound card? From: Alexander Pummer alex...@ieee.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, August 7, 2014 5:06 PM Subject: Re: [time-nuts] Low noise powersupplies to measure a power supply noise, better to say the noise spectrum, you would need a very large non polarized capacitor and spectrum analyzer, The input of the spectrum analyzer does not like DC, and has low impedance. Since spectrum analyzer's input impedance is usually 50 ohm, for to be able to see the noise at low frequency you need C = 1/( 2 x 3.14 x 50 ohm x f Hz ) capacitor, and you would need a DC level limiter to prevent blowing the input of the spectrum analyzer during the charge up of that capacitor. If you could get a hold of an old HP 1Meg to 50ohm buffer amplifier you would need much lover capacitance or if the buffer has AC input capability with low enough corner frequency like the Tektronix P6201 FET probe, you would not need any capacitor. And that would make your life much nicer since capacitors could generate noise to.. Charles Wenzel in his circuit collection files ha very nice good working noise reduction circuits. 73 Alex KJ6UHN ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low noise powersupplies
people who designing low noise PLLs solved that problem a while ego go to Charles Wenzels circuit collections he made a very low noise from DC to a few hundred kHz amplifier just to amplify the phase noise, here is: http://www.techlib.com/files/lowamp.pdf On 8/7/2014 5:05 PM, Bob Camp wrote: Hi A low noise chopper stabilized op amp can make a pretty good pre-amp to put in front of a low frequency spectrum analyzer. Something in the 20 to 30 db gain is adequate for most analyzers. That will get you down to a level that’s well below the noise floor on any OCXO I have ever seen. Here’s a way to look at it: The input resistors on the OCXO have KBT noise (they are real resistors). They also are in the “many thousands of ohms” range. If you short the EFC (zero noise in) you still have resistor voltage noise modulating the EFC. All you need to do is to get down to the KTB level in a few thousand ohm resistor. Yes 1/F noise does get into the mix. That’s why you want the chopper. Bob On Aug 7, 2014, at 6:32 PM, Alex Pummer a...@pcscons.com wrote: the PC sound card has limited bandwidth bellow 20Hz and above 20kHz, is nothing and also it is not so noise less like a spectrum analyzer which was made to analyze spectrum and the sound card self is in a relative noisy environment in the PC On 8/7/2014 3:09 PM, Bob Stewart wrote: What about a PC sound card? From: Alexander Pummer alex...@ieee.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, August 7, 2014 5:06 PM Subject: Re: [time-nuts] Low noise powersupplies to measure a power supply noise, better to say the noise spectrum, you would need a very large non polarized capacitor and spectrum analyzer, The input of the spectrum analyzer does not like DC, and has low impedance. Since spectrum analyzer's input impedance is usually 50 ohm, for to be able to see the noise at low frequency you need C = 1/( 2 x 3.14 x 50 ohm x f Hz ) capacitor, and you would need a DC level limiter to prevent blowing the input of the spectrum analyzer during the charge up of that capacitor. If you could get a hold of an old HP 1Meg to 50ohm buffer amplifier you would need much lover capacitance or if the buffer has AC input capability with low enough corner frequency like the Tektronix P6201 FET probe, you would not need any capacitor. And that would make your life much nicer since capacitors could generate noise to.. Charles Wenzel in his circuit collection files ha very nice good working noise reduction circuits. 73 Alex KJ6UHN ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
