i am making an Am transmitter and i need a 5 mH inductor for the 1MHz oscillator.
That is a very big coil to make yourself. It is too big to resonate at 1 MHz. About 70 microhenries would resonate with 360 pF at that frequency. It would be easier to get an oscillator coil from an old transistor radio and put about 300 pF across it. If fact it already covers about 1 MHz to 2 MHz with the existing tuning capacitor. If you want to make the coil yourself, use Wheeler's formula: The classic formula for single-layer inductance (air core) is called Wheeler's formula, which dates back to the radio days of the 1920s: L(N^2 times R^2) / ( 9 *R + 10 *H) where: L inductance in micro-Henries N number of turns of wire R radius of coil in inches H height of coil in inches In most countries, transmitters are not permitted on any frequency unless authorised, and especially not in the middle of the AM broadcast band.
