TX-500 500mW FM transmitter

These are materials that I used for coils in TX500. If you don't have required magnet wires I suggest you buy them from Radio Shack. They have a great deal of three spool magnet wires (first picture above) for only $4.69 comparing to mouser.com that offers 1/2lb of a single choice for as much as $18. The package in Radio Shack includes 14 meters of 22AWG (.065mm) wire, 25 meters of 26AWG (0.4mm) wire and 65 meters of 30AWG (0.25mm) wire. Second picture shows a miniature ferrite beads that I found in my junk box. If you don't have any of these and can't find them you may also use many other types which I will try to post soon. Radio Shack also sells a package of 30 mixed chokes and coils for very low price. There are two small components that may replace the use of four small beads that you will need. In other words one such component looks and does exactly the same job as two ferrite beads connected together as on a picture below. If you can't get any ferrite beads you may replace L4, and L7 (4 beads) with a regular air coils. I will post more information about that soon.

The above pictures show all finished coils that I used in TX500. They are very easy to make and there are always many alternatives in you can't find any needed part.

3.5 turns of 0.5mm / 24AWG magnet wire on 5mm diameter.

This is a high precision tunable coil. It is a pre-made coil that I took from a high quality FM radio from my junk box.
If you can't find anything similar then don't worry. Make a regular air coil similar to the one below (L2, L8) but only with 3.5 turns.
Just so you know, you may use any kind of wire thickness starting from 0.4mm to 1.5mm as long as the coil will be made the same way.
I even tried 0.25mm wire once and it worked fine but these wires are very fragile and you don't want to use such a thin wires in an oscillator - unless you put a resin on it to make it firm.

L2, L8:

4 turns of 0.65mm / 22AWG magnet wire on 5mm diameter.

1. Cut 9cm (3.5") of wire (1mm - 0.2m / 18 - 30AWG wire is fine as well).
2. Make 4 complete turns a shown on the pictures.

L3:

4 turns of 0.65mm / 22AWG magnet wire on 9mm diameter.

1. Cut 13cm (5") of magnet wire (1mm - 0.2m / 18 - 30AWG wire is fine as well).
2. Make 4 complete turns (as in L2, L8) on a 9mm diameter or a pencil.
3. Spread it to approximately 0.6mm

L4, L7:

4 turns on two small ferrite beads of 0.25mm / 30AWG magnet wire.

1. Cut 9cm (3.5") of magnet wire (you may also use a thinner wire with the same ferrite bead or thicker but then you will need a larger bead).
2. Make 4 turns. The first picture shows one complete turn, four turns will be complete when you will see four wires in the upper part.

These small beads are perfect to use in the transmitters up to 1W, above that I suggest you use a larger beads and a thicker wire.

L5:

4 turns on a ferrite bead.

1. Cut 10cm of 0.25mm / 30AWG magnet wire.
2. Make 4 turns on one small ferrite bead as shown on the pictures.

L6 (choke):

20 turns of 0.65mm / 22AWG wire on a ferrite ring.

If you don't have this type of ring try looking in an old computer power supply. (They may come in a different colors but they certainly will do the same job).

Build your own LC Meter and start making your own coils and inductors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils. LC Meter can measure inductances starting from 10nH - 1000nH, 1uH - 1000uH, 1mH - 100mH and capacitances from 0.1pF up to 900nF. The circuit includes an auto ranging and "Zero Out" function to make sure the readings are as accurate as possible ... [more]