[time-nuts] Thunderbolt - any negatives ?
Mike Monett
xde-l2g3 at myamail.com
Fri Jun 19 21:24:20 UTC 2009
> 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
helped.
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
http://pstca.com/spice/pstpp/pstpp.htm
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:
http://pstca.com/spice/ripple/ripple.htm
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.
Mike
More information about the Time-nuts_lists.febo.com
mailing list