Ok so in this instructable i will show you how to make the simples AM transmitter, it doesnt have a lot of range but i'm working on it, and If YOU find a way please let me know.

Ok so you will need the following stuff

-Tuning knob(variable capacitor)
-Antenna coil(i will post a How to on How to make one of these in the first step.
-680 Ohms resistor
-100K resistor
-470K resistor
-0.0022 Micro farads capacitor(0.022 also works)
-A C945 transistro(All the ones i've tryed so far have worked, as long as its PNP and low voltage
-A pair of old earphones.
-two 1.5 voolts batteries, and battery pack.

Notes, sometimes works as a metal detector :O
https://www.instructables.com/files/deriv/FEN/JGF3/FQJZNS7A/FENJGF3FQJZNS7A.MEDIUM.jpg

The first non-breadboard version:
https://www.instructables.com/files/deriv/FK6/UOAW/FQSWZI9L/FK6UOAWFQSWZI9L.MEDIUM.jpg

https://www.instructables.com/files/deriv/FP9/ENV9/FQSWZI9K/FP9ENV9FQSWZI9K.MEDIUM.jpg

https://www.instructables.com/files/deriv/F35/QFJP/FQSWZI9J/F35QFJPFQSWZI9J.MEDIUM.jpg

The PCB i got from my PCB box, saw wich copper lines went where and soldered my components on it(i was lucky, it's a hard way to make stuff but it happened :))

an basicly just used hot glue to glue everything to a battery pack...

Step 1: The Antenna Coil How To.

To make the antenna coil you will need the folloiwng

-two long strands of Copper wire like 3 meters each (with some sort of varnish isolating it)
-ferrite
-Electrical tape.
https://www.instructables.com/files/deriv/FN1/RUTJ/FQHNMVEA/FN1RUTJFQHNMVEA.MEDIUM.jpg

then start wrapping the first starnd around the ferite and secure with electrical tape
https://www.instructables.com/files/deriv/F3R/AEKI/FQHNMVFN/F3RAEKIFQHNMVFN.MEDIUM.jpg

then secure that loose bit with more electrical tape, and with that same tape put the other starnd of wire around the ferrite.
https://www.instructables.com/files/deriv/FIQ/00FD/FQHNMVGQ/FIQ00FDFQHNMVGQ.MEDIUM.jpg

you will have four loose wires, conect the midle two together, so u have three loose wires(like the photo)

TIPPP: when you antenna coil looks like the one in the pic, with a lighter or match burn the tip of the wires(just like a second, just to remove the varnish...

WARNING!!!! the antenna coil shown on the pic has very litle wire, so it doesnt work. yours should have much more wire wrapped around the ferrite.

If you want(recomended) solder a single core plastic wrap wire to each of the loose copper wires(best for breadboard) and make the middle wire have a diferent colour(so u dont get confused)

Step 2: Making the Transmitter

right, We have the antenna coil all we need to do is start making it :)
Grab the transistor and place it so that the round thingy is pointed towards you
https://www.instructables.com/files/deriv/FGP/AU9A/FQHNMVBN/FGPAU9AFQHNMVBN.MEDIUM.jpg

conect RED WIRE(minus of battery) but yours can be any colour you want.
to the same side of the transistor as u see on the pic! very important!!!!
https://www.instructables.com/files/deriv/FXU/5Y9Y/FQHNMVBM/FXU5Y9YFQHNMVBM.MEDIUM.jpg

Grab the 0.0022 micro farads capacitor and place either terminal of it on the middle terminal of the transistor, and the other somewhere else(as long as it doesnt touch anything else)

https://www.instructables.com/files/deriv/FU2/B2SR/FQHNMVBL/FU2B2SRFQHNMVBL.MEDIUM.jpg

put the 470K resistor in the middle terminal of transistor aswell, and the other side somewhere else as long as it doesnt touch anything else

https://www.instructables.com/files/deriv/FV0/OUM4/FQHNMVBG/FV0OUM4FQHNMVBG.MEDIUM.jpg

grab the 680 ohms resistor and place it once again to the middle terminal of transistor(cant touch anything else either)

https://www.instructables.com/files/deriv/FNS/7AJ1/FQHNMVBA/FNS7AJ1FQHNMVBA.MEDIUM.jpg

grab the 100K resistor and place it in middle terminal of the transistor, once again cant touch anything.

https://www.instructables.com/files/deriv/F5H/SI40/FQHNMVB7/F5HSI40FQHNMVB7.MEDIUM.jpg

Conect microphone to the 470K resistor and the left terminal of transistor(the one with the - polarity of battery)
And the middle wire of the antenna coil to the 100K resistor

https://www.instructables.com/files/deriv/FAO/DF50/FQHNMVN2/FAODF50FQHNMVN2.MEDIUM.jpg

connect green wires to the lateral wires of the antenna coil, and the tuning knob(the green wires closest to you on the pic(the ones on the back or just something else)

and connect another wire to the 100K resistor( this will be the + of the batteries)

https://www.instructables.com/files/deriv/F37/45EY/FQHNMVNP/F3745EYFQHNMVNP.MEDIUM.jpg

A schematic for those that didnt understand anything i sayd...(all lol)
https://www.instructables.com/files/deriv/FBX/2Q02/FQHNMVO2/FBX2Q02FQHNMVO2.MEDIUM.jpg

NOTESSS: With the old earphones you can cut the earphones off, and keep the cable and plug, conect the wires to the places where the Microphone is, and the plug to your MP3 Phone, PSP, i conected it to a pocket recorder.

https://www.instructables.com/files/deriv/FTZ/PZ30/FQHNMVPL/FTZPZ30FQHNMVPL.MEDIUM.jpg

Then get a radio(AM or short wave) tune to a station with no channel comming in, just static, turn on your transmitter, adjust the transmitter's tuning knob, untill you hear high pitched sounds fromn the radio, turn on your MP3, or whatever your using, and make the final adjustments, it should reach about 2 meters, not much but enough to impress some people, and there are ways to make it stronger... i just dont know 'em yet xD, anyways 2 meters is ok for something that will cost about 2$ to make... so good luck ;)

17 Comments

admin

14 years ago

This is a great Instructable, but you need to add a main image of the final project to the intro step. Please do that and leave me a message when you have so that we can publish your work. Thanks!

AirraB

6 years ago

it just me??? i see in the pic that u didnt use the given resistor???

i dont understand because all resistor is connected in the middle of transistor but in the schematic not all -_-

studleylee

8 years ago

Please add the schematics and images linked to. Then if saved as PDF is more complete.

This is great and useful for tracing power lines underground. If you clamp or place the transmitter near the metal ground of the power box going into your house, you can then use a radio( type that has the ferrite rod antenna ) to find the path of the under ground cable.

My boss showed me this trick: Just point the radio's rod (might have to disassemble the radio to see its orientation.) then tune to the transmitter freq. You will hear a noticeable null when directly over the wire. It will be loudest on just off to either side of the wire and fade with distance away from the wire. It worked up to 4 feet soil depth for me and I found the path right to the pad mounted utility transformer.

paleologos_the_greek

14 years ago on Introduction

very good job my friend as for the range with the c945 you ll not get too much try to use an SF 116 pnp transistor. operates on frequencies up to 60mhz so it is ideal i use this in an fm+am oscillator at 27mhz (kit by kemo) and it gives 1watt at 9v and 2watts @ 15volt (but for voltages over 9.8 volts requires heatsink!)