finding or making an inductor

I am trying to build a am transmitter. I am trying to make the inductor that is used in the tank circuit. It is a 200uH inductor. While taking apart a random electronic piece of junk I found a toroid, but it had no wayof identifying it. The diminsions are approx. OD 14mm ID 8mm H 6mm. It is also iron powered because it stuck to a refrigerator magnet. So basicaly if you could tell me the toroid part number or something that would be nice, and the number of turns and size of wire I need to get 200uH.

Wind 10 turns on it, and measure the inductance, preferably at 1MHz

I dont have an inductance meter. I consider getting one, but I just don;t want to spend the money. thanks anyway.

If you have an RF generator and some kind of detector or power meter you can find the inductance by guessing at approximate value and put a capacitor in parallel that would resonate it at desired frequency. Lightly couple the RF generator and a detector via capacitors of less then 1% of the parallel resonating cap.

Sweep the frequency and see where the output peaks. This will be the true resonate frequency for the known capacitor put in parallel. Calculate the inductance value based on the known parallel cap value and the actual measured reasonate frequency. You can also calculate the coil's Q by measuring the -3db drop off points either side of peak reading. The RF gen and detector must not significantly load the tank or Q will decrease as result of their loading.

When done properly, with confidence in known value of parallel cap and RF gen freq accuracy, this method can give better accuracy then most inductance meters.

LOL I dont have a rf generator either.

Build a simple Colpitts oscillator with known capacitor values and measure the frequency with a scope or frequency counter. Begin, as suggested before, with 10 turns.

It is also iron powered because it stuck to a refrigerator magnet.

Click to expand...

Not necessarily… ferrite will also “stick” to a magnet quite nicely.

indulis said:

Not necessarily… ferrite will also “stick” to a magnet quite nicely.

Click to expand...

Except ferrite IS iron

Not to hijack this thread but I have a schematic that describes what to build an inductor with but finding the part, The author of the book MORE EVIL GENIUS PROJECTS has a ultrasonic generator that it lists the parts but no such parts (have yet to locate) EXCEPT from the author
inductors needed -8- 1 mh inductor (6080)
2 - Hitachi 30.48 E cores and mating bobbin --- wind 50turns of #24 magnet wire wr2 Am thinking the 30,48 stands for size in mm??

I have a schematic of a Colpitts oscillator to make sure it would work but I dont see the add atatchment button. I saw the post where it said go through paint,and I have done all of that. I just cant find the that buton. By button I mean the thing you click on. I dont have an a frequency counter or scope but I do have the Basic Stamp 2 microcontroler. Maybe I could use that.

Looks like like no matter what I do is spend money on something whether it be a frequency meter or a inductance meter. so I will make it simple and buy a cheap LC meter off of ebay. thanks for the advice, and sorry for wasting your time

If you want to build radio circuits, then the LC meter will come in very handy. But, I should warn you about using orphan toroids from "a random electronic piece of junk." Unless the toroid came from a tuned circuit in a piece of radio equipment, then there is virtually zero chance of it being suitable for radio use. Most toroids that are removed from junked consumer electronics will be so lossy at radio frequencies that they will be utterly useless. You are better off winding an air core coil, or else buying a proper toroid made from type 61 ferrite material.

I will keep that in mind about "orphan toroids". It sucks that that it wont work well in a radio circuit.

The "type" or "quality" of the ferrite material can range by a value of more than 1,000 and this will determine the number of turns you put on the "ring."
It could be anything from 20 to 150 turns of 0.25mm winding wire.