[time-nuts] Low noise powersupplies
bob at evoria.net
Thu Aug 7 18:09:02 EDT 2014
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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