Nothing prohibits an iron powdered toroidal core to be used, but like in
many other applications the circuit Q is what counts and a coil wound over
an iron powdered core probably far exceed requirements.
For matching purposes an air core coil can have a satisfactory Q and
withstand consistent power levels while feromagnetic toroidal wound coil
don't perform so well were high impedance and consistent power exist.
If the used power is anyway small, may be a toroid wound coil is surely
applicable in the matching but also an air core coil size can be reduced
(keeping a reasonable Q) using a smaller wire size and smaller spacing
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