[TowerTalk] Station Noise

[Roger (K8RI)]

Jim Brown wrote:
> On Fri, 16 Oct 2009 22:59:44 -0400, Roger (K8RI) wrote:
>
>   
>> Not being the patient type I'd expect the dealer or factory to fix it.  
>> If not promptly addressed they'd find in on the loading doc some 
>> morning.
>>     
>
> I strongly agree. Many modern appliances are being sold with 
> electronically controlled variable speed motor drives. These units are 
> NOTORIOUSLY BAD RFI generators. Tell your dealer to either fix it or 
> replace it, and make it clear that it's on HIS nickel, not yours. This 
> product violates Part 15 of the FCC rules. 
>   
Unfortunately...those devices are exempt from part 15 IIRC.

73

Roger (K8RI)
> BTW -- I'm just working my way through Henry Ott's new book on EMC. It 
> includes specific advice for these variable speed drives. 1) Run a 
> dedicated equipment ground conductor between the controller and the 
> motor, following PRECISELY the same route as the current-carrying 
> conductors, and in VERY close proximity to them. This forms a 
> transmission line for the noise, providing a return path that has a very 
> small loop area. 2) Add a good power line filter between controller and 
> the power line, carefully bonding the ground of the filter to the ground 
> of the controller with a ZERO LENGTH wire. This is a two-step process, 
> and you need both steps. #1 is probably the most critical, but both are 
> important. 
>
> A third step that also helps must be done by the motor/controller 
> designer -- add a ferrite bead and small bypass capacitor to the gate of 
> the switching elements to slow down the rise time a bit, which reduces 
> the high order harmonics of the square waves that drive the motor. 
>
> 73,
>
> Jim Brown K9YC
>
>
>
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