[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
http://www.prc68.com

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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