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Ok – here’s the info regarding the Toroid Inductor:
[[i:3b8ae508d3]This has been slightly edited from an email with an engineer I know who has helped me build MLR[/i:3b8ae508d3]]
Sure that can be done, but it won’t yield as high efficiency as the air coil. With a toroid coil, smaller wire has to be used; the wires resistance lowers the Q of the coil. Then there are losses in the ferrite as well. The best Q for RF frequencies is with air coils and large wire.
That said: I use a FT-240-77 core for the low power AM transmitter that resonates with the 30pf antenna (a 108″ whip). That works out to about 130 turns of #24 gauge wire on the FT-240-77 toroid at 1700. A 108″ whip is 30pf and 9′ of the 1/2 inch copper pipe is 34pf. To calculate the inductance the formula is 1 divided by 39.4 x frequency (squared) x the above capacitance. The toroid comes with a chart of wire size vs. turns for a given inductance.
NOTES: The type 77 core saturates at about 7 watts.
Get your core here: