Why does anyone use a ferrite toroid for anything??
Ferrite cores are used for RFI suppression chokes, where we *want* losses.
73, John W1JA
-----Original Message-----
From:
[email protected] <
[email protected]> On Behalf Of Andrew Kurtz via groups.io
Sent: Tuesday, October 19, 2021 9:36 PM
To:
[email protected]Subject: Re: [nanovna-users] "Q", Coils, toroids, and guesswork?
I am really getting a lesson here! I have a homemade coil of 40 turns on a Clorox bottle, so length about equals diameter, intended to be best Q possible. Q is 130 based on X and R reported by nanoVNA at 1 MHz, where I use this coil. Note that this coil has 60 FEET of wire, and skin effect (I assume) makes R = 11 ohms or about 100 times DC resistance.
Then I wind 6 turns on my mystery ferrite toroid, using 10 INCHES of wire, and I get about the same inductance (180 uH versus 200 for the large air-core coil). And of course I get about the same reactance at the same frequency¡¡ but R rises to 200 ohms at 600 kHz and over 1000 ohms at 1 MHz!! I guess there is hysteresis, eddy currents, etc., but I expected that this much smaller coil with much less wire would be the best Q possible short of having litz wire¡ but the Q of the toroid is around 1. Why does anyone use a ferrite toroid for anything??
Anyone know where I can acquire some litz wire?
Andy
On Oct 19, 2021, at 7:23 PM, Jim Lux <jim@...> wrote:
On 10/19/21 3:48 PM, W0LEV wrote:
What could be higher Q (lowest possible losses) than air or vacuum?
Ferrite and powdered iron toroidal cores have a higher ?r which
yields higher inductance per turn than free space, but there are
associated losses. Air core inductors are the highest Q attainable,
all other variables being equal. Anything wound on ferrite or
powdered iron cores will exhibit lower Q than wound in free space.
Dave - W?LEV
Oddly, not necessarily. Yes, the same windings, with a core, will have higher L and lower Q, because of core losses. However, if you compare equal inductance and current handling ability, you might wind up with a LOT of turns (and a very long wire) so the wire losses are higher than the core losses on a inductor on a core.
