[time-nuts] Totally unrelated, but..

jimlux jimlux at earthlink.net
Thu Dec 8 10:05:17 EST 2016


On 12/7/16 9:34 PM, Hal Murray wrote:
>
> kb8tq at n1k.org said:
>>> the cool thing about those parts is that their PSRR extends
>>> up to several MHz.  A lot of LDOs have good PSRR to kHz.
>> Which to bring it back to noise in radios ….. could be the issue there. The
>> device isn’t oscillating, it’s just not blocking the crud from upstream.
>
> Would a simple L-C type filter on the input side solve that?
>
It would be difficult to get the kind of rejection the 3042 gives you 
with a *simple* LC, you're looking at 80 dB or better from DC to 3MHz
See the attached figure.   A multisection filter with carefully chosen 
components can do it.

The usual "solder in" bulkhead feethroughs (e.g. Spectrum Controls), for 
instance are ok at higher frequencies (70dB above 10 MHz), but pretty 
bad low down.  So you're looking at a discrete design.


they've even got an ap note on how to *measure* this, which is no easy feat
http://cds.linear.com/docs/en/application-note/an159fa.pdf
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