FM Tracking Transmitter

For some time I had been wanting a tracking transmitter for my rockets. As my rockets became larger, and flew higher it soon became apparent my flying field needed to be larger. The answer was easy, my family owns a one square mile area of land with no roads on it, a perfect launch area. The only problem, from about mid June through September the land has row crops on it, making finding a rocket that may land 1/4 mile away a near impossible task.

Early on I experimented with the FRS radios. They were inexpensive and had decent range. The problem was they were difficult to make directional. While I may use them in future rockets for simple data transmission, I don't think they will work well for tracking.

So I searched the Internet for other transmitter plans. I wanted the design simple, inexpensive and no license required to use it. A small FM transmitter seemed to meet those requirements. I downloaded about 6 different designs, and built four of them. The design that worked the best was found at http://www.jbgizmo.com/index.html The owner of the site sells a kit to make this transmitter, as well as offers the plans on the web site for free. Please note, the author of that site makes the plans available for free for personal use, commercial use of any kind would require a license from the owner. There isn't a lot of sense in duplicating his site here, but sites come and go, so I'll at least give you the information on how I put this little transmitter together. If you really want to make it easy on yourself, order his kit, it has a board with all the circuit traces on it. All you have to do is solder the parts onto the board.

I need to point out again I am no electronics guru. Perseverance is a great asset, and I do tend to stick with it until I get it right. This little transmitter can be built by anyone, it may not work on your first try, but just keep working on it. I recently bought a small bread board to test circuits on. A bread board allows you to plug in components and connect them with little jumper wires, so no soldering is required. It's a great way to test without ruining components. Radio Shack has them for a reasonable price, make sure you pick up a set of jumper wires too.

I built the circuit on the bread board first, and it worked perfectly! So I went ahead and built it on the little 1.5"x1.5" printed circuit boards I use for my timers. After construction the transmitter did not work, so I went through with a magnifying glass and rechecked every wire and solder joint. I found one solder joint I missed. After resoldering, the transmitter again worked perfectly.


Above is the schematic of the transmitter. It is my own strange way of drawing the circuit, it is the bottom view, or, as viewed from the side you solder on. To me, it is easier to see it this way, as this is the side you do all the soldering on. The red dots are places where you solder. I used 24 gauge solid copper insulated wire to connect everything. The wires all run on the bottom of the board (the solder side), the components are all on the top side of the board. The nasty looking squiggle lines are resistors, the short parallel lines with a number between them are capacitors, the one with an arrow through it is the variable capacitor. I didn't use the proper electrical symbol for the 2n2222 transistor, to make it easier I just used the pin labels e, b and c as seen from the bottom of the board. Again, it makes it easier for the layman (like me) to follow.

Here is the parts list:

Resistors:

1) 4.3 Meg Ohm

1) 1 Meg Ohm

1) 100 Kilo Ohm

1) 10 Kilo Ohm

1) 220 Ohm

Radio Shack has a resistor variety pack you can use. The largest resistor in the pack I bought was a 1 Meg Ohm, so to get the 4.3 Meg resistor I used four 1 Meg resistors in series (end to end to end to end), resistors in parallel would reduce the resistance (go the wrong way).

Capacitors:

1) .1 uF

3) .01 uF

1) 5 pF

1) 22 pF

1) 6 to 50 pF Adjustable ( not real fussy here, but should have a low end value of under 10, and a high end value under 60)

Radio Shack again sells all these. The .1 and .01 uF capacitors come in two packs. The small pF capacitors you can get in a value pack. The adjustable capacitors are not available at all Radio Shack stores, I saw an assortment pack of trimmers and chokes and it may have one in it, but I'm not certain. You can get all this from Digi Key also, it would be cheaper too, but they have a $5 charge on small orders, and then shipping on top of that.

Semiconductors:

1) 4011 Quad NAND gate

1) 2N2222 transistor

Odds and Ends:

1) 14 pin IC socket

1) 9 volt battery clip

1) 213 hole general purpose PC board (snap in half)

1) Solid Wire for antenna

1) Coil (Note: 6 turns of 26 gauge magnet wire wound on a 1/8" form and removed. Then stretched to about 3/8" long.)

I'll post more here after I've used the transmitter a few times.

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