germanium radio
Radio seems to be a high hurdle, but it is a really easy production of germanium radio. All you need is a diode IN60 and a crystal earphone.
you need : Germanium diode (IN60), enamel wire, wrap core, crystal earphones (general magnets are not allowed), antenna wire 5m, 2 aluminum plates, plastic bag, variable capacitor (taken from the radio of 100 yen shop) Cheapest), resistance about 10KΩ
回路図
The figure above is the circuit diagram. Look at what is written in the words on the right. To put it simply, connect a coil, a capacitor, a resistor (not necessary), and a crystal earphone in parallel, and insert a diode in the middle. Connect the antenna and ground to both ends of the coil. I don't care about the orientation
Compare the photo with the schematic. The orientation doesn't matter at all. The upper right is the actual radio.
The upper part catches radio waves. As for the coil, wrap the enamel wire around the core of the wrap like the center. Please wind it 100 times or more. (If the number of turns is too small, radio waves cannot be captured.) The variable capacitor has a wrap sandwiched between two 15 cm square aluminum plates (aluminum foil).
Coil is L = μN * N * S / l (μ: magnetic permeability, N: number of turns, S: cross-sectional area, l: coil length)For capacitors, C = εS / d (ε: permittivity, S: area, d: distance between electrode plates) The value changes by changing the size and length of the coil and capacitor. Substituting those two numbers into the conductor below will determine the frequency of the radio you can hear, but you won't know until you actually make one.
f is the frequency received. If this number is 954KHz, it means TBS radio. Channels can be created by changing the area of the capacitor and changing the number of coil turns. And you can listen to other stations as well. In this case, change the overlapping area of the condenser (aluminum foil).
About antenna and ground
Antennas are generally made by extending a few meters of conductors outdoors. You can drop a few meters of wire from the window. The ground is originally connected to the ground, but since it is a very weak current, a human may hold it on the opposite side of the coil from the antenna. It works well as a ground. As long as the ground and antenna are solid, you can listen to some stations even if they are sloppy.
It's hard to see in the photo on the left, but there is a diode between the coil and the earphones. You can still hear it. You can also use a commercially available variable capacitor for radio instead of the aluminum capacitor.
Try attaching a radio bar antenna instead of a coil and try various things. Radios for 100-yen shops are made with this principle in mind. So, don't you think 100 yen is amazing?
Experiment 2: Let's make a transmission circuit that can send radio waves
Let's make a broadcasting station by skipping radio waves by ourselves. I feel like I need some great equipment. However, when electricity is applied, radio waves always flow around it. Simply put, radio waves are constantly being generated around electrical appliances.
As shown in the figure on the left, when electrons vibrate up and down a metal rod (antenna), radio waves as shown in the figure are generated.
Radios, TVs, etc. transmit this at a constant frequency. It is difficult to always emit accurate frequencies and strong radio waves, but this time we will generate and receive weak radio waves that do not cause much trouble to the surroundings.
you need: Radio cassette player, two coils with about 200 turns, amplifier, speaker
Caller
As shown in the picture above, connect the coil to the audio terminal of a radio cassette player or the like. This alone will convert the audio into a wave. As the audio current circulates in the coil, it vibrates as a result.
receiver
On the receiving side, attach an amplifier to the coil and connect it to the speaker. If you don't have an amp, you can somehow hear it by connecting it to a crystal earphone.