[RFI] Snap-on RFI suppression core size vs cable size
w8bya at mchsi.com
Mon Aug 21 10:25:28 EDT 2017
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
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
> The Original Rolling Ball Clock
> Idle Tyme
> On 8/21/2017 7:10 AM, David Robbins wrote:
>> I scanned a few papers this morning that talk about things like the
>> 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
>> 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 at arrl.net
>> web: http://wiki.k1ttt.net
>> AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
>> -----Original Message-----
>> From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of Jack
>> Shirley N8DX
>> Sent: Monday, August 21, 2017 01:00
>> To: N1BUG
>> Cc: rfi at 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
>> IDs as you mention?
>> On Sun, Aug 20, 2017 at 7:06 PM, N1BUG <paul at 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.
>>> Paul N1BUG
>>> RFI mailing list
>>> RFI at contesting.com
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