[Elecraft] CFL

[Jack Smith]

The CFL's I've analyzed and disassembled have small switching power 
supplies, usually running around 40-50 KHz.

If you are a VLF/LF listener, you can see the emitted signals up through 
several hundred KHz. Many sidebands can be observed, at multiples of 60 
Hz from the central frequency (which is unstable).

Usually, though, not much can be heard about 1 or 2 MHz if your antenna 
is separated by a few tens of feet from the lamp.

If you have a defective CFL, disassembling it can be educational. First, 
you will see many components stressed at or above their maximum ratings. 
I've seen some with the filter caps operated with voltage above the 
maximum rating.

Second, it's not uncommon to see the PCB with holes and traces for EMI 
filtering, but the parts are not installed. I assume that the parts are 
installed in some prototypes to meet EMI specifications and then are 
omitted to save money.  I don't believe the CE approval markings mean 
anything to the Chinese manufacturers.

I've written a bit about CFLs at 
http://www.cliftonlaboratories.com/compact_fl.htm

Jack K8ZOA