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Build your own Crude FM Radio || FM,AM Tutorial


Recently, I found this dirt cheap FM transmitter module for around three dollars By connecting 5V to the power inputs and selecting the MP3 port I can hook up my frequency generator to send out my favorite song called 1KHz sine wave Then I can power up my old-school radio select the FM range and fine tune the frequency until I can hear my song [80 to 1000 hz sine wave sound] I could also select the microphone inputs solder a small antenna to the board and talk with you, the viewer, through radio signals But my radio itself is very bulky and impractical So in this video let’s find out how radio FM Communication works and how you can build your own crude, but very simple FM receiver Let’s get started [Traditional GreatScott! intro song] First of, we need to take a closer look at the FM Transmitter circuit And because probing several components with my oscilloscope did not clarify the function principle at all I went ahead and used my multimeter with its continuity function to create a schematic of the circuit At the start, we have our audio source which get AC coupled to our first amplifier stage The transistor and LC resonator built up a high frequency oscillator In our case around 100MHz which is also called the carrier frequency But this oscillation alone does not contain any information from our audio signal we want to transmit Or does it? By applying an alternating voltage onto the base of the transistor Like our audio signal The base collector capacitance changes Which in consequence changes the resonance frequency And thus our oscillating signal now changes it’s frequency a bit Proportional to the amplitude of the music This is called FM or Frequency Modulation Just what we wanted In comparison to that, in the earlier days people used AM Or Amplitude Modulation, to listen to their music It’s a similar principle We just change the amplitude instead of the frequency of the carrier wave in proportion to the amplitude of the audio signal Only problem is, that the audio quality is not that great to listen to And even my FM transmitter produces AM along the way Because it’s a poor man’s version But we can ignore it for now At the end of the circuits we got another amplifier stage to stabilize the signal Which is then sent out through an antenna Now to build a FM receiver, I found this very simple one from MicroE.com The working principle is similar Only in reverse and by changing the input power resistor to a 25 kΩ potentiometer With a fixed 5 Kilo Ohm resistor and adding a LM386 Audio Amp with complimentary parts I wanted to give the circuit a try The necessary components are easy to find and also quite cheap Which is always nice But you need to make the coil yourself I use 0.65 millimeter enamel copper wire and a four millimeter drill for this Just wrap the copper around the drill four times while trying to keep everything tied together Then use sandpaper to remove the isolation at the beginning and end of the coil And you are done Really not that hard My coil has a length of around 3 millimeter and a diameter of 5.3 millimeter The inductance can be calculated with an approach formula which gives me a value of around 0.15 microhenry And by assuming a capacitance of let’s say 20 picofarads We get a resonant frequency of 92 Megahertz Which seems legit So we can start to solder I recommend a small piece of perfboard with copper dots In addition, It is also worth mentioning that you should keep the pins of your components as short as possible And the whole wiring well packed together Once the circuit was complete, I soldered on a ridiculously long antenna And used an 8 Ohm speaker or even earbuds to listen to the op-amp output It is easy to hear that there are a lot of unwanted noises But on the other hand, it also picked up my sine wave song without a problem I even was capable to listen to AM and FM radio stations sometimes Which is not bad for such a small amount of components But in the end, this is clearly not a substitute for your commercial radio at home Those often prefer ready-to-use IC’s which offer an awesome quality boost But that is a project for another video. Until then, don’t forget to like share and subscribe That would be awesome If you want to support the show in order to keep the videos coming Then please consider supporting me through my patreon campaign Stay creative and I will see you next time

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