[time-nuts] Thunderbolt - any negatives ?

Brooke Clarke brooke at pacific.net
Fri Jun 19 18:55:02 EDT 2009

Hi Mike:

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.

Have Fun,

Brooke Clarke

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
>   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
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