Introduction: Radio Transmitter
This radio transmitter sends an AM radio signal, which can be recieved at a frequency of 819 kHz.
This project is made by Applied Physics students from the TU Delft, in the Netherlands. It is part of the course DEF.
- Oscillator chip CD4007
- 21 breadboard cables
- 2 resistors (1 kOhm)
- 2 resistors (10 kOhm)
- Capacitor (27 pF)
- Capacitor (470 nF)
- AUX cable, which will be cut in half
- Battery (9V)
- Battery case
- Copper tube, 2 metres tall. This will be used as the antenna
- Stand, to keep the copper tube antenna upright
- Copper wire, about 50 cm
- Device with music (your phone, for example)
- Wire stripper
- Sanding paper
Step 1: Oscillator Chip
Each hole in the breadboard has a coordinate, with a letter (horizontal) and a number (vertical). The Oscillator chip is placed in the middle of the board, occupying rows 12 to 18, colomns e and f. Important is the small indent in the chip, this has to be pointing to the top of the breadboard, which can be seen in the picture.
Step 2: Breadboard Cables and 1 KOhm Resistors
In the picture, different color cables are used to make the process easier to follow. However, you do not have to follow these colors, because they have no effect on the transmitter.
12d - 20b
17g - 20c
4f - 20a
4j - 9j
9g - 1g
1d - most right + column
12g - most right + column
15g - most right + column
Resistors (1 kOhm):
4g - 4i
1e - 1f
Step 3: Breadboard Cables, Capacitor and 10 KOhm Resistors
8h - 9h
9i - 16g
14d - 20h
13g - 20g
18g - 20i
Capacitor (470 nF):
6i - 8i
Resistors (10 kOhm):
20f - 23f
23g - 26g
Step 4: Breadboard Cables and Capacitor
13d - 30b
15d - 30c
25f - 30d
16d - most right minus column
17d - 25j
18d - most right minus column
Capacitor (27 pF):
23j - 25j
Step 5: AUX Cable
Cut the AUX cable in half and strip the cables.
Cut the 2 extra breadboard cables in half and strip these too.
Step 6: Connecting the AUX Cable
The AUX cable has 3 outputs: 2 plastic cables (with copper wires inside) and 1 bundle of copper wires (this is called the ground, the wires have no plastic casing).
Connect one piece of breadboard cable to each of the AUX outputs, by twisting the small copper wires together. To make the connection more permanent, the copper can be soldered together. However, this is not necessary.
(The fourth piece of breadboard cable will be used in step 9, don't lose it!)
The ground is plugged into the most right minus column. The other two cables coming from the AUX are plugged into 6f and 6g.
Step 7: Power
Place the 9V battery into the battery case. Two cables come out of the battery case, a red and a black one. The red cable has to be plugged into the most right plus column, and the back cable goes into the most right minus cable.
Step 8: Making the Antenna
At first we want to make it clear that it is not necesary to build an antenna for the signal to be received, however it boosts the range significantly. At first we used a breadboard cable as antenna, by only plugging one end of the cable into the breadboard. However, to get a signal to your radio, you'll have to hold the cable against the receiver of your radio. Because we wanted to be able to move the radio away from the transmitter, we created a bigger antenna to boost the signal. A copper tube is used as the antenna, sending the AM signal to the radio.
Most copper tubes you buy in the store are coated with Copper-Oxide. You cannot see this layer, but it bocks the signal from the breadboard cable to the antenna. Therefore, the layer has to be removed with sanding paper. Not the whole tube has to be sanded, only about 10 cm of the end of the tube where the connection with the breadboard is made.
The antenna can be placed upright by putting it into a stand. Pay attention: keep the sanded part of the tube at the bottom.
Step 9: Connecting the Antenna
The antenna is connected to the breadboard with copper wire. Use half a breadboard cable and connect it to one end of the copper wire. This can be done by twisting the copper together. The connection can be soldered together to make it more permanent. However, a small piece of duct-tape would work aswell.
Plug the breadboard cable (with the copper wire attached) into the breadboard at coordinate 30a.
Next, the end of the copper wire is twisted around the sanded part of the antenna. Use duct-tape to make the connection to the tube more secure.
Step 10: Using the Radio Transmitter
Turn on your radio and put it on channel AM 819 kH. Connect your phone (or another device) to the breadboard using the AUX cable and turn on some music. Set the sound of your device to the maximum, to create the strongest signal.
You should hear your music now through the radio. If the signal has too much static noise, try to alter the channel frequency a bit or move the radio around until you recieve a better signal.
The transmitter works best if the radio is about 1 meter removed from the antenna.