> It's been there all along guys.
> "http://www.lairdtech.com/Products/EMI-Solutions/Ferrite-Products/Ferrite-Toroids/";
Hi Lee,
Laird does not have complete data on all of their cores. For example...
For higher power applications and to avoid heat, especially with unknown
load situations, we want a core that has low loss tangent or high Q.
For good suppression, especially with unknown load situations, we want high
loss tangent and Q.
These two contradict each other, so a balance must be struck between system
common mode performance and core heating. Laird mostly only provides Z,
which tells us nothing about ratios of resistive part (to suppress common
mode and avoid resonances in a wide variety of applications) and reactance
(to provide a high inductive reactance, to not load the circuit with loss).
Consider an air-core choke balun. Since Q is high, I can insert an air core
balun in a feedline and make the common mode much worse! All the talk about
"ohms reactance" is meaningless for broad use of an air core choke. If the
choke is 20 j2500 ohms and I stick it in a feedline at a point where common
mode impedance 30 -j1251 or more, the choke will make things WORSE.
If we added a large pure resistance the choke would dissipate energy, but it
would increase common mode impedance for ANY load impedance.
Z is not enough.
There are pages on the internet, and articles everywhere, telling people how
to build air core baluns, Yet air core baluns can actually make systems
worse, I would guess maybe as much as half the time in random systems! I
don't think this is an intentional conspiracy to mislead people. It is just
that authors can't possibly think through things, especially when there are
probably only a handful of people who really understand a complex problem in
great detail. I don't believe very many, if any, in this hobby intend to lie
to people just to mislead them, although that message probably does play
well to the Grassy Knoll crowd.
I think the major problem is most people have the best intentions, and are
enthusiastic, but don't always completely understand how or why things work.
Sevik for example wrote a nice book about baluns and ununs, which is 99%
great, but did not understand balance or common mode. He published a balun
design that actually forces ANY load into imbalance, and that balun made its
way into commercial products. That wasn't intentional, or the result of any
grand larceny on the community.
Laird does not give data they should give to help people make a wise choice.
This doesn't mean they are bad people, it just means they miss addressing
the real problem with critical information................which is pretty
common.
FairRite probably has someone somewhere, probably on the outside, who is
experienced in common mode suppression and drives the data they provide, so
the data is much better.
It's an imperfect world with limited time, and many of the imperfections are
not based on being a crook or "less-than".
73 Tom
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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