[time-nuts] Low noise powersupplies

[Alex Pummer]

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.
> 73
> Alex
> KJ6UHN
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