[Elecraft] Noise sources

[Jim Brown]

On 1/2/2012 8:23 PM, Richard Fjeld wrote:
> It is simply a 12V incandescent bulb.  Apparently the small metal box in-line on the power cord is a switching PS instead of a step-down transformer.

YES. This is a VERY common noise source, and finding a step-down 
transformer for products like this can be quite difficult.  The problem 
is that while 12VAC will run the device just fine,  the available 
mounting space is just large enough for a switching power supply, and 
far too small for a transformer. If you go to an electrical supply store 
to buy one, they will sell you an unmarked box with wires coming out 
that they call an "electronic transformer." What's inside is a very 
noisy switching power supply. MAYBE it will have a UL label, indicating 
safety agency compliance. and MAYBE that  will be real, but UL standards 
say NOTHING about EMC.

I'm told that it is possible to buy clean power supplies for low voltage 
lighting, but I've never managed to do so.

73, Jim K9YC