Date: Thu, 17 Jun 2021 16:15:34 -0700
From: Dan Maguire <danac6la@gmail.com>
To: towertalk <towertalk@contesting.com>
Subject: Re: [TowerTalk] New tool - toroidal ferrite core inductor
calculator
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
====================================
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.
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.
### Tnx for the prompt reply. The reason I mentioned about the use of
more than 3 x cores is in my case, I have 200 feet of RG-393 teflon
coax available, and the max number of turns that will fit inside a 2.4
inch OD core is 7. Thats 7 passes through the cores, before coax
terminations are made. 213-U is the same deal, only 7 turns max, with
no connectors.
## The 160 and 80 m cm chokes are both made with 7 turns of RG-393 on
5 x type 31, 2.4 inch OD cores. Thats 5 k ohms on 160m, 7.6 k on
80m...and 5 k ohms on 40m. The actual 40m cm choke is made with only
6 turns on 5 x cores..which results in 6.2 k ohms....so slightly higher by
1.2 k ohms, with one less turn.
## I used 2 x identical CM choke assys in series, each in its own
8x8x4 nema box, with gasketed lid etc. On paper, this should result in
10k on 160m, and 15.2 k on 80m, and 12.4 k on 40m. The goal was to
get at least 10 k.... which should result in a 40db reduction in CM
current. If gasketed nema boxes are used, put some Permatex dielectric
grease on the rubber gasket, before closing the lid. Mine are all air
tight..and filled with a large package of silica gel / desiccant. I only
operate at night, so solar effects are a non issue. If I have done the
maths correctly, the actual dissipation of the stack of 5 x cores in each
box is miniscule.
## On a side note, I have one of danny horvath's CM chokes which covers
160-10m. It consists of 9 turns of RG-303 on 2 x type 31, 2.4 inch OD
cores.... which is then in series with 12 turns of 303 coax, on another 2 x
cores. Both stacks go into the same box. 7.7 k on 160, which then
increases a bunch, like 8.8 k on 80m..and keeps increasing, as freq
increases to a max of 11-12 k on 12m..then back down to 10 k on 10m. On
each band, RS is > XS, which was the goal.
## heres what does not work very well, and thats a binoc configuration.
We managed to get one to cover 3.2 to 4.4 mhz....and thats it... like
6.4 k. Useless on 7 mhz/ 40m band. Binoc configs are extremely narrow
banded, and very tricky to get to work....like work on one band. I dont
recommend them.
Jim VE7RF
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