[time-nuts] Thunderbolt - any negatives ?

Mike Monett xde-l2g3 at myamail.com
Fri Jun 19 17:24:20 EDT 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




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