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.
Dave - WØLEV
On Sun, Feb 9, 2020 at 12:56 AM Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 2/8/2020 4:15 AM, Rob Atkinson wrote:
> > Why do hams mindlessly use ferrite on everything, including lines that
> > only have DC on them? What happened to RF chokes and bypass
> > capacitors, which when the correct component values and specifications
> > are used (value, current handling and voltage rating), will work
> > better and cost much less?
>
> You may be confusing differential mode with common mode. And with modern
> electronics, DC often has a strong AC component. That's what's going on
> with variable speed motor controllers and switch mode power supplies.
> And, sadly, lots of equipment is poorly designed, with common mode
> emissions and common mode susceptibility. Ferrite chokes solve common
> mode problems. Traditional RF chokes and bypass caps solve differential
> mode problems.
>
> 73, Jim K9YC
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--
*Dave - WØLEV*
*Just Let Darwin Work*
*Just Think*
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