[RFI] buying a AC adapter

[Dale]

Aaron,

Get yourself a linear power supply.  The linear that tore up your SW listening may very well have had a self-oscillation problem in the series regulator chip.  (The popular 78-series regulators are supposed to have by-pass caps at (or near) the input and output terminals.  Many cheapo manufacturers get by without those critical caps because the chips will usually work just fine without the caps - for awhile.  They can become power oscillators at any time.

If you don't have any hamfests or thrift stores handy, check out the selection of linear wall warts at Jameco Electronics or Marlin P Jones & Associates.  Both are on-line and offer many linear supplies.  If you find one with the correct voltage and current, but not the correct conenctor for your equipment, buy the unit anyway and cut off and save the output cable from the old switcher.  You can always wire it into the new linear wall wart and you will then have the correct (and quiet) power source with the proper connector.

73, Dale
WA9ENA 


-----Original Message-----
>From: Aaron Kreider <aaron at campusactivism.org>
>Sent: Apr 26, 2013 6:29 PM
>To: rfi at contesting.com
>Subject: [RFI] buying a AC adapter
>
>What should I look for in an AC adapter for low RFI?
>I know that switched adapters tend to be bad.  However, I also used to 
>have a bad linear adapter cause RFI directly to a shortwave radio that 
>was plugged into it.
>
>I'm looking for a new adapter for my router.  9V.  600ma.  center 
>positive.  2.5 mm x 5.5 mm.
>
>Are class 2 adapters mostly or entirely linear?  I looked at some 
>adapters and they either say switching or class 2.
>
>Are switched power supplies considering smaller than linear?
>
>Thanks,
>
>Aaron
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