[TenTec] Switching Power Supplies

[Jim Brown K9YC]

On Mon, 15 Mar 2010 14:17:10 -0400, Gene Henderson wrote:

>What kind of noise are we looking at here.Don't want to seem dumb but , I 
>have used several switching supplies and to this date I have never had a 
>problem that I am aware of. 

Broadband RF trash. Harmonics of the 10-20 kHz square waves used internally 
within the supply. They often show up a carrier that floats slowly up and 
down the band (because the osciillator that generates the square wave is 
"dithered" to reduce emissions at any one frequency when measured in an EMC 
compliance lab). Can also show up as broadband hash. 

Switching power supplies are now the most common form of power supply, used 
for everything from wall warts for cell phone chargers and computer 
equipment to big battery chargers and TV sets. The only time you're likely 
to see one that's fairly quiet is if it's designed and sold specifically 
for use in radio systems (like those reviewed by QST). 

73,

Jim Brown K9YC