On 12/7/16 9:34 PM, Hal Murray wrote:
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
On 12/7/16 9:34 PM, Hal Murray wrote:
>
> kb8tq@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
