[Elecraft] Switching Power Supplies

[Larry East]

I believe that the "trick" for successfully using a switching power supply 
is to keep the receiving antenna far away from the poser supply -- which is 
admittedly  difficult in field operations -- since the hash is usually 
radiated rather than transmitted via the power cord. In the rare instance 
when hash reaches the receiver via the power cable from the supply to the 
receiver, wrapping several turns of the power cable thru a large 77- or 
43-mix toroid as close as possible to the power supply should take care of 
the problem.

I have used a Radio Shack 3A switcher and a small laptop switcher (modified 
to give 14V rather than 18V output) with my K2 and neither caused any 
problems when using an antenna outside of my house, or when using them in 
my motor home with an antenna mounted on the back of the vehicle. However, 
if I use an "indoor" antenna within a few feet of either power supply, I 
can hear an assortment of "birdies", "hash" and other bad stuff -- not very 
loud, but loud enough to be objectionable.

So, as someone else mentioned, use an outside antenna and good grounding -- 
good ideas in any event.

72/73,
Larry W1HUE/7