I think Dave meant to link this document by K9YC - . It¡¯s the one where he compares a number of different types (#43, #61, #73, #78, etc) and why he often prefers #31. But he has good things to say about #43 as well! Also #61 and #73 in some circumstances. This document is a GREAT read!!
Randy
NC8U
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On Jan 27, 2020, at 8:13 AM, David Eckhardt <davearea51a@...> wrote:
All the data he presents in the referenced paper uses 31 material. The
type of choke I referred to is shown in Figure 3 of the paper. I see
nothing nixing 43 or other material (31 and 73) in the paper. He does
present variation of ?r with temperature. Any and all my the chokes
(Figure 3 or 9) do not heat more than 10 C or so above ambient with
5-minutes of key down time at 1 kW. However, a lower ?r is needed for
bifilar wound common mode chokes which is shown in Figure 9.
I wound several of these bifilar CM chokes (Figure 9) on 43 material. One
was wound with a double insulation of two different ¦År's which, due to the
insulation, increased the inter winding capacitance to a point where the
high ?r combined with increased ¦År precipitated a resonance near 6 MHz.
When connected to my antenna system at legal power, it arced badly - no
surprise. Most of the CM bifilar chokes I wound and tested using 43
material showed resonances above 50 MHz. Once again, between the VNA and
in practice at legal limit, I proved to my self the red iron powder cores
are best for this type of CM choke (Figure 9) at HF. That is what is now
in place in my antenna system - 450-foot long doublet fed with parallel
conductor transmission line. For the chokes illustrated in Figure 3, yes,
the higher ?r ferrites are more applicable.
I should comment that the final solution in my application drastically
reduced the noise picked up by the feedline (open wire) from the
(unfortunately) new appliances inside the house (built in 2014). These
days, ALL appliances contain multiple SMPS's which come from China with
absolutely no attention paid to EMC/RFI. The advice given in the paper
regarding installation of a CM choke or current balun at the feedpoint and
at the shack end of the feedline is golden. Try it. You will be amazed at
the noise reduction.
Dave - W?LEV
On Mon, Jan 27, 2020 at 3:54 AM stone_ridge_road <xdavid@...>
wrote:
I agree that this topic is outside the general outlines for this list,
but then again I didn't bring it up. For anyone who would actually like
to understand what makes a good common mode choke, though, I refer them
to K9YC's paper (which is based both upon theory and careful VNA
measurements on over 250 samples) that explains why types 73 and 43 are
not good choices.
73,
Dave AB7E
On 1/26/2020 6:30 PM, David Eckhardt wrote:
I rest my recommendations on measuring many using the HP 8753C vector
network analyzer. For current baluns, the high ? materials yield more L
per turn and, consequently, offer more choking capability. 73 and 43
material are great for these applications. Bifilar wound common mode
chokes are a whole different ball of wax. Again, I refer my
recommendations to many hours of winding and measuring with the HP 8753C.
This is off topic forthe NANOVNA site and, likely, should be taken
elsewhere.
Dave - W?LEV
On Mon, Jan 27, 2020 at 12:19 AM stone_ridge_road <
xdavid@...>
wrote:
That's not really a very good suggestion. As K9YC has s stated a
zillion times on the TowerTalk reflector, type 31 material is pretty
much the only really good material for a common mode choke at HF ...
primarily because it has considerable internal loss and the other
materials don't.
Also, the number of turns is fairly important ... "as many as you can"
isn't necessarily a good idea because you're trying to optimize the
combination of the interwinding capacitance and the coil inductance to
create a tuned circuit for the range of interest. As K9YC has pointed
out, a poorly chosen combination can actually act a series tuned circuit
and totally defeat its purpose. He doesn't even recommend coax for the
chokes any more ... simple paired windings of #12 THHN actually works
better due to shorter lengths and lower interwinding capacitance.
Don't take my word for it, I'm only the messenger. Jim has done a ton
of work, both theoretical and experimental, to support his arguments.
It's all available on his website.
Dave AB7E
On 1/26/2020 3:45 PM, David Eckhardt wrote:
I presume your are using coaxial cable? To make a choke (current)
'balun', I'd use a ferrite with high permeability (43, 75, 71, or 35
material). This configuration should consist of winding coaxial cable
multiple times (as many as you can get without overlapping) through the
large core. Even ferrites aimed at reducing EMC will work fine as they
have a very large ? and loss within the ferrite material. This type
of
'balun' forms an inductive (reflective) choke for common mode currents
on
the outside of the coaxial braid. For bilaterally wound common mode
chokes
at HF, the red powdered iron core (? of 10) is best, but start with the
current choke.
Dave - W?LEV
On Sun, Jan 26, 2020 at 10:11 PM rickstealey via Groups.Io
<rickstealey=
[email protected]> wrote:
Have you looked at your antenna impedance? Unless it is a terminated
antenna such as a Beverage the feedpoint Z is going to vary all over
the
place, nowhere near 450 ohms. Ex: when it is 1/2 wavelength long it
is
a
high z, and when it is a quarter wave it will be around 50 ohms IF it
has a
counterpoise. A receiving antenna does not really have to be well
matched
to your feedline to be effective.
Rick
--
*Dave - W?LEV*
*Just Let Darwin Work*
*Just Think*
