# Inductance

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#### sIL80

##### New Member
Hi all! I plan to make a small Fm transmitter, and one of the elements is a variable inductor "6.5 turns no. 26 enam on .25 inch form with ferrite slug". Whats the inductance for it? I dont want to make it myself, and i just want to buy a premade variable one, so whats the range of incuctance?
Its a 9V circuit, and i plan to broadcast between 90-100 Mhtz, if that helps. Thanks

#### k7elp60

##### Active Member
Well it is pretty difficult to tell the inductance from what you say are the charactestics, because the Mu of the ferrite will affect the inductance. If there is a capacitor in parallel with the inductor, knowing the value will help in calculating the approximate inductance. If you take the formula LC=25330/f^2 (in Mhz). Use the lowest frequency (90mhz). LC is the product of inductance in uh and capacitance in picofarads. In this case LC=25330/(90^2) or 25330/8100, LC=3.13 L=3.13/capacitance in pf.
Then look for an adjustable inductor with this as the maximum L.

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