[time-nuts] Low noise powersupplies

[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


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 <alex at 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 <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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