[RFI] Motors/controllers and something to think about

Jim Brown jim at audiosystemsgroup.com
Wed Aug 15 22:40:03 PDT 2012

On 8/15/2012 10:30 PM, Roger (K8RI) wrote:
> The issue has dealt with specific makes and models with and without RFI,
> but as PWM is by its nature an RFI generator we need to stop and think
> about how companies (any company) acquires the motors and speed controllers.

It is critically important to realize that it is EASY to build a PWM 
system without RFI if you simply pay attention to the fundamental laws 
of physics  -- keep track of where the current flows, ALL of the 
current, including DC, baseband AC, and RF -- and design your product so 
that it flows in loops that have small cross sectional areas, and over 
wires that don't make good antennas.  It's really as simple as that.  
The most recent edition of Henry Ott's classic text on EMC even has 
chapters devoted to switching power supplies and PWM motor controllers.

73, Jim Brown K9YC

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