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Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
They are very simple. Usually they just consist of 5 or 6 turns of enamelled wire (a 20 AWG is a good size, but thats not very critical) wound around a Pencil or any round object of about 1/4 inch in diameter.
You than remove it, clean off the insulation at the ends a bit and put it into the circuit.
You may need to stretch the coil lengthwise to get it to operate at the correct frequency.
I like to wind my coils around the inside part of a bic pen. It makes them very small so that they don't get in the way of other stuff. Of course you will have to increase the capacitance of the LC circuit. wutever suits you best :lol:
one question. is magnet wire the same as enameled wire?
Use google to search 'air coil inductance calculator' and you will find some information and calculators. Amateur radio references contain quite a bit of this information. Some may be found on line at ARRL and similar websites.
Worth noting is that even the smallest physical changes such as the distance between the windings can result in variations in inductance. In some circuits vibration or physical movement of the circuit board or chassis can affect the circuit. Winding the coil on a form or using some dope to secure the windings can be helpful. Coupling to other parts of the circuit or radiation might also be of concern. Changes in the position of things that are nearby can also impact the performance - at high frequency bringing your hand or finger close to some circuits can cause a slight drift. When experimenting these are things to know about but otherwise ignore by keeping the board still, keeping hands/tools away, etc.
Check out My Calculators at: **broken link removed**
These Inductance Calculators are More Accurate than most on the Internet and cover a "Much Wider range of Wire Sizes".
But Calculating Very Tiny Inductances, Such as used in FM Coils can be done, But Winding them Exactially or Even Measuring them Exact is Difficult. Both these will cause Errors.
Accurate Measurements and using My Calculators will Definately get you within 5%.
For the antenna, you can either use 1/4 wavelength or 1/2 wavelength. Do you know about wavelengths? hopefully you do or this will make no sense.
If you're transmitting @ 100MHZ 1/4 wavelength is 75cm and 1/2 wavelength is 150cm.I'm not sure what the difference is in using 1/4 as opposed to 1/2.
One thing that I dont yet grasp because i haven't found any suitable calculations/explanations is impedance matching (gotta get one of them aarl handbooks). This applies very much to antennas.
OTHER TIPS:
1. DO NOT assemble it on a breadboard
2. When testing it, make sure you have your radio 10 feet from the transmitter. The transmitter can overload the radio.
3. Make sure you have your transistors in the right position.
4. Test your battery before you plug it into the transmitter. a low battery can cause all sorts of weird strange things.
5. When you tune the variable capacitor, a screwdriver will mess up the frequency. Just when you think you hear the transmitter come over the radio as you're tuning the capacitor, when you take the screwdriver off, the frequency will change. A way to get past this is take a plastic knife, and shave it down so that it fits in the variable cap. it helps a lot :lol:
The reason that the screwdriver does this is because it becomes part of the capacitor and changes the capacitance.
6. Use this calculator to determine your base frequency i dunno if chemelec has a base frequency calcultor. if he does, use his, its probably more accurate.
Pike-for this kind of work the best advice is to keep leads and other conductor lengths short - at least for the RF portions of the circuit. I'd suggest trying the protoboard and keep the components close together, put them as close as possible to the board. The leads to the battery certainly can't be short. Just do the best you can and see where you come out. Like others, you'll eventually get a sense of how much effort you have to put in to compactness.
You might take a quick look a the little kits that are available to get a sense of what to do.
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thanks gary and zachtheterrible but i also need to know some basic equations to calculate the iductance 
