Published on May 25, 2017
The objective: In summary, I learned many things while making this radio. I did some experiments and learned from them, too. Radios have many parts; capacitors, diodes, sometimes resistors (not in my radio), earpieces, and wiper blades. There is also a lot of equipment that is needed; wire cutters, soldering irons, etc. But, most importantly, I had fun and an experience that will always make me euphoric. I am so glad I chose to make a radio!
The crystal radio got its name from the crystal (i.e. mineral) in it. Crystals can detect radio waves, so they are used in some radios. The crystal vibrates, creating a sound.
The way the radio works is that the radio stations broadcast a radio wave. The radio wave influences the electrons in the antenna, which influences the electrons in the coil. Through a process called induction, the coil creates a pulsing electrical current in the whole radio.
The pulse rate can be adjusted with the wiper blade or the capacitor. Adjusting the capacitor also changes the volume.
Finally, the electrons go through the diode, which only lets electrons through one way, from one of the two connections and to the crystal in the earpiece, which vibrates and makes a sound.
Radio stations send radio waves into the air so people can hear what the radio station wants them to. To do this, the radio stations convert sound waves into radio waves that are exactly the same. Then, the radio station makes an upside-down copy of the radio wave and puts it together with the original radio wave. Then, the radio station fills it in with the station’s frequency so that the radio can tune in to it
The purpose of building a radio was, for me, to be able to listen to radio stations. The secondary reason was that it might be possible to hear aliens with a radio. To hear aliens would be a great scientific discovery. I also wanted to see if I could learn how to build a radio, and how a radio works.
At first, I built a more complicated radio with electronic components that can be bought from a store, but it didn't work as well. It probably would have worked better if I had understood it more. So, I decided to build a radio that was more simple and made of household objects.
I had fun soldering things in the first radio!
My hypothesis for the first experiment was that when the antenna was coiled, it would work. I also thought that when the antenna was uncoiled on the ground it wouldn't work and when it was in the air, it would work.
My hypothesis for the second experiment was that when there was more surface area of wires touching the ground connection, there would be better quality sound.
My hypothesis for the third experiment was that tuning to the same station with different capaciror and wiper blade positions would be possable, but I thought it would be harder. I also never expected that there was an inverse relationship between the coil and the capacitor.
My hypothesis for the fourth experiment was that the sensitivity (how much the wiper blade can move but stay on the same station) of a radio satation was the width of the wire used to make the coil (0.5mm).
• Tin Foil
• 6.5 centimiter long peice of any conductive metal
• 15 meters of wire (covered in plastic except for on the ends)
• 2 cardboard toilet paper rolls (1 large, one small)
• Wooden board
• Electric Tape
• Duck Tape
• Alligator clips
• Electrical socket
Experiment #1 The effect of changing the antenna’s condition on the radio’s reception.
The experiment’s purpose was to find the effect of what happens when the antenna is coiled or uncoiled. First, the antenna was be coiled and connected to the radio. Then, the earpiece was listened to. Next, the antenna was uncoiled and hung from a tree. Again, the earpiece was listened to. Finally, the antenna was completely disconnected from the radio and the earpiece was listened to.
Experiment #2 The effect of changing the ground’s condition on the radio’s reception
The experiment’s purpose was to find the effect of what happens when the ground is disconnected. First, the ground is disconnected. Next, the earpiece is listened to. Then, the surface area of the wires touching the ground connection is decreased and the earpiece is listened to.
Experiment #3 The relationship between the capacitor and the coil (AM CKNW 980)
In this experiment, the relationship between the capacitor and the coil was explored. To do this, first a radio station was tuned into (AM CKNW 980). Next, the position of the wiper blade on the coil and the overlap of the two capacitor cylinders was measured. Then, the outer capacitor cylinder was moved. After that, the wiper blade was moved to tune into the original station and their positions were recorded. This was repeated four times. To make sure the correct station was tuned into, another radio was used and constantly kept on AM CKNW 980 to compare.
Experiment #4 The sensitivity of wiper tuning
In this experiment, the distance the wiper blade can be moved but still have the radio tuned to the same station was studied. To do this experiment, the radio was tuned into a station. The wiper blade was moved in one direction until the radio was about to be un-tuned
There is no sound when the antenna is coiled. There is sound when the antenna is uncoiled. It seems that when it is coiled it isn’t receiving sufficient amount of radio signals to run the radio. My hypothesis about the antenna in the air was right, but my other hypothesises were wrong.
Antenna Coiled On the Ground Antenna Uncoiled on the Ground Antenna Uncoiled in the Air
No Sound Quiet sound Sound
When the surface area of the wires touching the ground was decreased, the sound became harder to hear. The opposite happened when the surface area was increased. When the ground was disconnected, there was no sound. This result is consistent with the principle of operation of the radio, since the electrons must flow to the ground to allow the radio to operate. My hypothesis for this experiment was correct.
It is possible to tune into the same station by changing both the wiper blade and the capacitor the correct amount. The following table summarizes the distances of the wiper blade and the capacitor cylinder overlap. My hypothesis for this experiment was partly correct.
The following table summarizes the sensitivity in terms of wire width. My hypothesis for the fourth experiment was correct.
I learned many things from making a radio, such as how to solder, I learned more html that a had forgotten, how radios and electricity work, how radio stations broadcast sound, and how many of the electric components that I used in the radio work. If I got another oppourtunity to make a radio, I would probably be able to use my time and radio parts more efficently. Or, another experiment to do could be to see if the radio could be used as a power source. The purpose of this science experiment was to make a working radio. This was accomplished. I was suprised to find that the second radio worked slightly better that the first one, because the second one was more simple. I did four experiments and learned more about how radios work while I did them. I also now know more about what is done at SETI.
Science Fair Project done By Mathew