[Elecraft] switching power supplies

[Rick Shindley]

Switching power supplies are a noise sources, but very convenient travelling
companions!  If you find a switcher that seems to be "noise free", try
powering it from a variac over the range of possible input line voltages
(and various load currents) to see if it remains quiet over the frequencies
you intend to operate. You could be disappointed!

Switchers have a tough time limiting the noise they introduce common mode
into the power line. Common mode noise is easily converted to differential
mode noise in your receiver by way of high Z "ground" paths and even antenna
selection!  Better to not use a switcher at all in a radio application if it
can be avoided.

For many, they work just fine but there are no guarantees!  It would be
interesting to hear from people for whom the switchers HAVE NOT worked well.
Theory is one thing, the real world is another. Are there horror stories out
there waiting to be told?

Rick KC0OV
K2 1360 (on a linear supply)