It is as simple as the ferrite material you have is very lossy. There
are much better ferrite materials to use at 1Mhz.
With a proper core and litz wire, you can get the R under 1 ohm.
???????????????????????????????????????????????????? Mikek
On 10/19/2021 8:36 PM, Andrew Kurtz via groups.io wrote:
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.
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