[RFI] Multi-Stage High Efficiency Air Conditioner Units

[Jim Brown]

Yes. Common mode chokes can correct for serious design errors and the 
penny-pinching cost reductions made by the bean-counters that degrade 
the RF immunity of the product. Common mode chokes applied to noisy 
cables are non-intrusive to the design -- for example, they don't affect 
rise times that can seriously increase dissipation and cause equipment 
failure. Capacitors and inductors applied to the differential circuit 
CAN cause problems by affecting rise times.

As a SYSTEMS engineer who realizes the complexity of designing inside 
the box, I have always concentrated on solutions that are outside the 
box. And the differential circuit (like things that affect rise times( 
is often inside the box.

If you haven't already done so, I STRONGLY urge you to study the app 
notes on my website about "The Pin One Problem," which is, sadly, nearly 
universal, and the primary cause of hum, buzz, and RFI in practical 
systems. k9yc.com/publish/htm

In addition to adding ferrite common mode chokes to wiring that can act 
as antennas, the most important solution is proper bonding. That's 
addressed here. http://k9yc.com/GroundingAndAudio.pdf

73, Jim K9YC

  and the On 2/8/2020 5:58 PM, David Eckhardt wrote:
> One interview I ran while at HP trolling for a tech for our EMC group.  
> I asked the candidate what he though of ferrites.  I don't like specific 
> questions on an interview.  I'd rather ask general questions and see 
> where the interviewee takes it.  His answer, "Ferrites are our 
> friends".  I had to laugh a bit, but couldn't fault his answer.
> 
> If things are designed and executed properly with EMC/RFI in mind, there 
> should be no need for these clamp-on ferrite 'beads'.  However, few 
> designs are bullet proof and most times compromised by budgets. Ferrites 
> are useful as a band aide to a marginal of compromised design. They 
> should be deployed intelligently, not haphazardly.   I have to use them 
> generously on my wireless router to keep the RFI to acceptable levels 
> for radio astronomy.  I have no control over the design inside the box.  
> In addition, there is no common mode choke on my PC power supply for 
> economic reasons, I'm sure.  I put one there and its amazing how much 
> difference it makes.  Ferrites are a good thing so long as they are 
> installed intelligently.
>