[time-nuts] Thunderbolt - any negatives ?
brooke at pacific.net
Fri Jun 19 18:55:02 EDT 2009
I think it's National semi that has an app note talking about how the topology
relates to noise output. Some are bad others are much better.
Mike Monett wrote:
> > And be mindful that some frequency-standard devices contain
> > integrated DC-DC switching converters - like my HP 58540A GPS-DO.
> > The noise from the HP DC converters was spraying RFI every 100 kHz
> > or so on the HF bands. After trying various RFI abatement
> > measures, including additional bypass C and toroid-wound #31
> > ferrite material, my solution was scrap the entire PS board and
> > bring in clean power from a triple-output linear supply made by
> > Power-One. There's no switch-mode component anywhere in the path
> > of my GPS-DO.
> I'm having the opposite problem. The linear supply in my HP 53310A
> Modulation Domain Analyzer spews out a huge magnetic field that
> completely disupts any nearby equipment. For example, it causes a
> fuzzy trace and triggering problems on TEK 2467B scopes, which makes
> the scope unusable for low-level work. No amount of shielding has
> I'm seriously considering making the 53310A DC power section into a
> switcher. I have developed some techniques that greatly reduce
> crosstalk by mounting circuits on their own grounded platform. These
> have a minimum number of connections to the main system ground, and
> are chosen to minimize switching currents from flowing on the main
> system ground. I put a brief description of the PST Prototype
> Platform on my web site at
> Another technique that can help is adding an active filter to the
> output of the power supply. These can be very effective, but there
> are a number of approaches that are well-publicized that don't work
> very well. There is more analysis here:
> Finally, Linear Technology supplies Low Noise Switching Regulators
> that can give ripple values of less than 100uV, which is comparable
> to or less than many linear regulators. If interested, see the links
> in the above url.
> Noise can be a tricky problem, but the above information might give
> some ideas to help tame it.
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