Lesson 21 is the crystal radio project. A crystal radio is a radio that needs no electricity. Lesson 22 is the amplifier project. Lesson 23 is the AM transmitter project. The transmitter is so simple to build. Lesson 24 is the yagi antenna protect and it too is simple.
Radio project; build the radio
If you would like to build a crystal radio there are multiple youtube videos that take you step by step though the instructions on how to build a crystal radio. My advice to you is invest in one because if you are a teacher or a mom or even a kid, they are great and inexpensive.
Radio project; build an amplifier
Amplifiers are electronic components that amplifie a current or wave. An example of an amplifier is a speaker. Amplifiers are interesting because they are everywhere in your earbuds, in your phone, and in your speaker. They are in pretty much everything.
For an amplifier (speaker) you need Two 10 microfarad (uF) electrolytic capacitors, One 0.1 microfarad (uF)ceramic capacitor, Two 220 microfarad (uF) electrolytic capacitors, One 0.047 microfarad (uF) ceramic capacitor, One 10 kilo ohm potentiometer (variable resistor), One 10 ohm resistor, Simple on/off switch, One 9 volt battery ,Battery circuit attachment, Small speaker (8 ohms works), One LM386 amplifier chip or equivalent part, Amplifier chip socket, Perfboard, Solder and soldering iron and a Plastic jar. For instructions watch this video. For an amplifier for the earpeice you will need One 0.001 microfarad (MF or uF) capacitor, Two 1 microfarad (MF or uF) capacitors, One 10 microfarad (MF or uF) capacitor, One 82 kilo ohm resistor (82k), One 100 kilo ohm resistor (100k), One 10 mega ohm resistor (82M), One 2N4401 transistor or equivalent part, One 9 volt battery, Breadboard (for testing) and watch this video.
Radio project; build an AM transmitter
To build an AM transmitter you need One small transformer (audio or doorbell transformer), One oscillator chip(for AM radio frequencies – 540 kHz to 1.6 MHz), Sound source (CD player, iPod, etc.), One mini male phone-jack (1/8″ works), Four AA batteries, Battery holder case (4 AA slots), Breadboard, 24 gauge (AWG) wire or22 gauge also works. For the video it is here https://youtu.be/_4-Sx-T6VBc
The transmitter works by turning AC(alternating current) to DC(direct current) because AM frequency are AC but the radio needs DC to play sound. I think that is funny because if it can convert AC to DC, then why can’t it just accept AC?
Yagi and dish antennas
The dish works like a funnel with a filter it picks up all of the stations and then funnels them out. The yagi works with music wire and the music wire is the thing that pick up the stations and the radio filters them out. Antennas have to be half the length of the wavelength ex: 3 meter wave length 1.5 meter antenna. The gain of an antenna is a very technical measurement but, broadly speaking, boils down to the amount by which it boosts the signal. Bandwidth is the range of frequencies it can pick up. If you are interested in the yagi antenna (I am) you can build one with this video and some cheap supplies it is very interesting and I highly advise making one.
All and all crystal radios and some extra components are cheap and inexpensive. They are fun to build and they teach lots of great stuff. Some things are worth spending money on and this is one of them.