[time-nuts] Low noise powersupplies
alex at pcscons.com
Thu Aug 7 18:32:25 EDT 2014
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 <alexpcs at ieee.org>
> To: Discussion of precise time and frequency measurement <time-nuts at 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.
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