[TowerTalk] New tool - toroidal ferrite core inductor calculator

[Dan Maguire]

Jacek, SP3L, had some trouble posting so he asked me to relay his
answers to a few of the questions posed by VE7RF.  -  Dan, AC6LA

====================================

Hello Guys,

please forgive me if I do something wrong - I am using TowerTalk for
the first time.
Here are my answers to VE7RF questions.

>>> I noticed it will only handle a maximum of 3 x cores, why is that ? I use 5 x cores, type 31, 2.4 inch OD on both my 160 and also 80 and also 40mCM chokes.

Using N cores does not increase the inductor impedance. Actually, it
even slightly reduces it. Try calculating and displaying the following
inductors:
1x #43: 2.4/0.5" 14T
2x #43: 2.4/0.5" 9T
3x #43: 2.4/0.5" 7T

[AC6LA:  See https://forums.qrz.com/index.php?threads/new-tool-toroidal-ferrite-core-inductor-calculator.768222/page-5#post-5888198
]

If you increase the number of cores, you need fewer turns to achieve
the same frequency coverage and your core has greater volume so it can
dissipate more power. And that's it.

But if you take the same 3 cores, wind them individually and connect
them in series - that's quite another story. Your total choke
impedance will increase 3 times (both |Z| and R). That reduces both
the common-mode current and power that needs to be dissipated in the
choke. And you again have three cores to dissipate heat but as said
before less heat than before.

One more thing. Suppose that you calculated that every individual
chokes should have, say, 14 turns. You may decide to make three chokes
having 13, 14 and 15 turns and connect them in series. In this way,
your final choke will tolerate the spread of core permeability
parameters to a higher degree.

That's why I do not see much benefit in increasing the number of cores
in the calculator.

>>> It will  only handle a maximum of a 2.4 inch OD  type 31 core.  K9YCs latest designs all use  the much larger,  I think,  4 inch OD cores.

Unfortunately, we do not have enough data to cover accurately the #31
4" OD core. The permeability data provided by Fair-Rite is good for
small cores and still acceptable for the 2.4" OD core. But the
calculation would be inaccurate for 4" OD core. If somebody provided
us with enough credible measurement data of the #31 4" OD core, we
could add it to the calculator.

>>> As per number of turns, is this for wire, or coax,  or can be used for either ?   If coax used, what type of coax ?   I used  RG-303 and  RG-400 on the smaller  CM chokes....and  RG-393 on the bigger CM chokes.

Generally it is for insulated wire but I do not expect a significant
difference if you use coax.

>>> So while the  software may well  get you close,  one would still have to test the final assy...with a vna  or my method below.

Absolutely. I couldn't agree more. The calculation is just the first
step. The electronics designers say: the drawn schematics that is not
breadboarded and measured is worth less than the pencil and paper used
to draw it.