FairRite recommends three turns to take out the bias of the inherent
inductance of the wire, itself. Personally, I've done OK with a single
pass through the ferrite toroid. Trouble is with the multiple turns air
wound with out the toroid is that the air core needs to match (pretty much)
to the dimensions of the inductor on the toroid. One turn is easier but
less precise.
Dave - W?LEV
toggle quoted message
Show quoted text
On Sun, Apr 11, 2021 at 11:41 PM Kent AA6P <kawill70@...> wrote:
I have three different ferrite beads of the same size and would like to
know which one would provide the greatest EMI Suppression at 2.0 MHz. The
ferrite beads have a diameter of 0.5" and a height of 0.25".
Here is a description of the test I ran yesterday. I'd appreciate any
interpretation of the results.
My NanoVNA was calibrated at 2.0 MHz for testing on Channel 0. I attached
a 50 ohm carbon resistor with two one inch leads to the Channel 0 connector
and measurements were recorded. Ferrite beads were then inserted over the
resistor one at a time after temporarily disconnecting one lead.
50 Ohm Resistor: SWR 1.02, Smith Chart 48.9 ohms 29.3 nH
Ferrite Bead 1: SWR 1.11, Smith Chart 49.6 ohms 429 nH
Ferrite Bead 2: SWR 1.08, Smith Chart 49.2 ohms 293 nH
Ferrite Bead 3: SWR 1.02, Smith Chart 49.0 ohms 54.4 nH
A second test was run using a two inch piece of wire instead of the
resistor.
Two Inch Wire: Smith Chart 117 milliohms 93.8 nH
Ferrite Bead 1: Smith Chart 759 milliohms 495 nH
Ferrite Bead 2: Smith Chart 320 milliohms 361 nH
Ferrite Bead 3: Smith Chart 208 milliohms 125 nH
Any observations or comments would be appreciated.
I also have a question on the Smith Chart which traditionally has had a
Resistance Axis and a Reactance Axis. Is the NanoVNA simply translating the
reactance at the marker frequency to the associated capacitance or
inductance?
Thanks, Kent
AA6P
--
*Dave - W?LEV*
*Just Let Darwin Work*
