Re: [RFI] Snap-on RFI suppression core size vs cable size

[Gedas <w8bya@mchsi.com>]

Hi Joe. About a year ago I did just what you guys are talking about. I 
had purchased a whole bunch of assorted split bead cores of various 
sizes and shapes off Amazon. No specs with them but the price was so 
right that I picked up 40-50 of each flavor I could find.
At the time I did not have my HP-8712ES VNA so I used my AIM 4170 to 
experiment a little bit and just have some fun to see what my new cores 
looked like RF wise. I took a given core and tested it with 1-T, then 
2-T, then 3-T etc....then for fun put two of those cores in series (each 
with 1-T) to see for myself what effect the various configurations had 
on the impedance (real & imaginary) over frequency. Then tried 3 cores 
in series etc, etc.
It was interesting to see how superior a single core with multiple turns 
of wire worked vs. a single turn of wire through 2, 3, or even 4 of the 
same cores all placed in series with each other.
I may be able to find the plots that I saved and if you are interested I 
would be happy to share them with you. But I want to point out that Jim 
(K9YC) has already done all this hard work (and a whole lot more) and 
made those results along with an excellent narration available for all 
of us via his published papers. I am sure his test methodology and 
accuracy is far superior to what I did....again I was just messing 
around wanting to get a quick idea of what happened under different 
scenarios with my generic cores. 73
Gedas, W8BYA

Gallery at http://w8bya.com
Light travels faster than sound....
This is why some people appear bright until you hear them speak.

On 8/21/2017 9:34 AM, Joe wrote:
> Can you now do the same test, but see how the value changes with each 
> turn in the core?
> IE: loop it through 1 time measure 2x etc.
>
> Joe WB9SBD
>
> Sig
> The Original Rolling Ball Clock
> Idle Tyme
> Idle-Tyme.com
> http://www.idle-tyme.com
> On 8/21/2017 7:10 AM, David Robbins wrote:
> > I scanned a few papers this morning that talk about things like the 
> > ferrite
> > window fill factor and variations of inductance with wire size... then
> > pulled out my vna and a ferrite to try a quick experiment.  My 
> > conclusion is
> > that if the ferrite is much larger in diameter than the wire going 
> > through
> > it the inductance will be decreased.  My quick explanation of this is 
> > that a
> > current through a wire generates a magnetic field around the wire 
> > that is
> > strongest near the wire and gets weaker the farther away you go.  To 
> > get the
> > most flux in the ferrite in order for it to increase the inductance the
> > ferrite must be close to the surface of the wire.  my simple test 
> > with the
> > vna used a 22ga clip lead going once through a 2" diameter ferrite, 
> > when the
> > wire was in the middle of the core the |Z| of the single turn coil 
> > was like
> > 38 ohms, when it was touching the inside edge it increased to 42 
> > ohms, so it
> > appears to be a real and probably not insignificant effect.
> >
> > David Robbins K1TTT
> > e-mail: mailto:k1ttt@arrl.net
> > web: http://wiki.k1ttt.net
> > AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
> >
> >
> >
> > -----Original Message-----
> > From: RFI [mailto:rfi-bounces@contesting.com] On Behalf Of Jack 
> > Shirley N8DX
> > Sent: Monday, August 21, 2017 01:00
> > To: N1BUG
> > Cc: rfi@contesting.com List
> > Subject: Re: [RFI] Snap-on RFI suppression core size vs cable size
> >
> > I guess it would be too practical to take a VNA and measure Z with 
> > different
> > IDs as you mention?
> >
> > N8DX
> >
> > On Sun, Aug 20, 2017 at 7:06 PM, N1BUG <paul@n1bug.com> wrote:
> >
> > > I have re-read both RFI-Ham.pdf and KillingReceiveNoise.pdf twice each
> > > over the last couple of days. Great work which I refer to frequently,
> > > but neither really answers my question.
> > >
> > > Suppose I am trying to use common mode chokes to eliminate noise on a
> > > conductor at 144 MHz. Suppose the conductor diameter is 1/8 inch. This
> > > is VHF so we are not talking about multiple turns - just a wire
> > > passing ONCE through a ferrite core.
> > >
> > > A Fair-Rite 0431178181 (.161" ID) would be the best fit for this cable.
> > > According to the data sheet its Rs is about 180 at 144 MHz.
> > >
> > > The Rs of a Fair-Rite 0431164281 (.250" ID) is about 330 at 144 MHz
> > > but it fits the wire in question very loosely with a larger air gap.
> > > How much, if at all, will this "loose fit" reduce the effective Rs?
> > >
> > > Is the answer "it depends"? I've been trying to find an answer to this
> > > for years but I keep coming up empty. Maybe it's buried in the
> > > engineering talk which is over my head.
> > >
> > > 73,
> > > Paul N1BUG
> > >
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