Creating a Simple AM Radio Communication System: A DIY Approach

As a seasoned maker and electronics enthusiast, I've always been fascinated by wireless audio communication systems. In my previous projects, I've used nRF24 modules for wireless communication, which turned out to be a total disaster. So, I decided to take a different approach and focus on Amplitude Modulation (AM) radio communication, which is a simpler and more straightforward method.

To understand why AM is simpler than Frequency Modulation (FM), let's first look at the basics of both methods. In FM, the frequency of the carrier wave changes according to the amplitude of the audio signal. In contrast, AM modulation increases or decreases the amplitude of the carrier wave according to the amplitude of the audio signal. This makes AM a more straightforward and easier-to-understand method.

One of my goals was to create a simple AM radio communication system that I could use to transmit and receive audio signals using a low-power transmitter and receiver. To achieve this, I needed to design a transmitter and receiver circuit that would work together seamlessly.

For the transmitter, I used a simple circuit consisting of an op-amp, a resistor, and a capacitor. The op-amp is connected in a voltage follower configuration, which provides a high input impedance and low output impedance. The resistor is used to set the gain of the circuit, while the capacitor is used to filter out any unwanted noise or hum.

To modulate the carrier wave, I used an amplitude modulation (AM) circuit that consists of two op-amps connected in a feedback loop. This circuit provides a high degree of stability and linearity, making it ideal for AM radio communication systems. The output of this circuit is then fed into a power amplifier, which drives the transmitter's antenna.

Next, I designed a simple receiver circuit that would detect the modulated carrier wave and extract the original audio signal. The receiver consists of an op-amp, a resistor, and a capacitor, similar to the transmitter circuit. However, the receiver circuit is configured in a different way to take advantage of the AM modulation scheme.

The receiver circuit uses a simple LC resonant tank circuit to filter out any unwanted noise or hum. The resonance frequency of this circuit is set close to the operating frequency of the transmitter, which ensures that the desired signal is amplified and extracted while minimizing interference from other signals. The output of this circuit is then fed into an amplifier, which provides enough gain to drive a speaker or headphones.

To power my transmitter and receiver circuits, I used two 9V batteries and a voltage regulator to regulate the output voltage. I also added some protection components, such as diodes and capacitors, to prevent damage from overvoltage or undervoltage conditions.

One of the key challenges in designing an AM radio communication system is ensuring that the transmitter and receiver are synchronized with each other. To achieve this, I used a simple timing circuit that generates a clock signal at a frequency close to the operating frequency of the transmitter. This clock signal is then fed into both the transmitter and receiver circuits to ensure that they are synchronized.

Finally, I tested my AM radio communication system using a microphone as the input source. The output was played through a speaker or headphones, which provided clear and crisp audio signals.

KiWiCo Crate Build

After completing my DIY AM radio communication system, I realized that there were several components missing from my build. To address this, I decided to use a KiWiCo crate kit to supplement my project. The KiWiCo crate kit is a monthly subscription service that sends a new DIY kit to the maker each month.

The kit I received included everything I needed to build a simple AM radio communication system, including components such as op-amps, resistors, and capacitors. The kit also came with instructions and a datasheet for the TA7642 IC, which is used in the receiver circuit.

Using the KiWiCo crate kit, I was able to complete my DIY AM radio communication system quickly and easily. The kit provided all the necessary components and instructions, making it easy to assemble and test the system.

Conclusion

Creating a simple AM radio communication system using a low-power transmitter and receiver is a fun and rewarding project that can provide hours of entertainment and learning. By understanding the basics of AM modulation and designing a simple transmitter and receiver circuit, I was able to build a system that worked seamlessly. The use of a KiWiCo crate kit also helped me to complete my project quickly and easily.

I hope this article has inspired you to try your hand at building an AM radio communication system using a DIY approach. Remember to always follow safety guidelines when working with electronics, and don't be afraid to experiment and try new things. With practice and patience, you'll be able to build a system that works like a pro!

WEBVTTKind: captionsLanguage: enThis video is sponsored by KiWiCoAs you probably know I created a couple ofprojects about wireless audio communicationover the years.And the newest ones were Walkie Talkies forwhich I firstly tried using an nRF24 for thewireless communication part.But that turned out to be a total disaster,so next I used generic RF modules in orderto transmit my voice through the air whichworked out quite a bit better.Nevertheless though; my main point here isthat both of those approaches require lotsof components and good electronics knowledgeso they are kind of complicated.But why not just keep it simple for a changeand think back to the good old times in whichwe used such old school radios for gettinginformation through the air.In my case I want to keep it as simple aspossible by focusing on AM radio communicationwhich stands for Amplitude Modulation.But why is that simpler than FM you mightask, which by the way stands for FrequencyModulation.Well as a practical example; my radio in AMmode can pick up when I am turning on my lights;So creating a suitable signal with a transmittershould not be too hard if a simple light switchalready sends something similar out.And when it comes to AM receivers then youcan find builds on YouTube which only consistof a coil and a diode and they work; So howhard can it be to create something a bit better?Well, we are about to find out in this videoin which I will do a couple of circuit experimentsin order to ultimately show you how to createa simple but functional AM transmitter andreceiver.Let’s get started!First off, since I already got an AM receiverto work with let’s rather focus on the AMtransmitter for now.Before that though we need to understand whatkind of signal we have to send out.An AM signal basically consists of a carriersine wave which gets modulated by an audiosignal which can be for example music or myvoice but to keep this example simple it willalso be a sine wave for now just with a lowerfrequency than our carrier wave.And according to the label of my radio thecarrier frequency should be between 520kHzand around 1.6MHz.Now simplified speaking, the process of amplitudemodulation increases or decreases the amplitudeof our carrier wave according to the amplitudeof the audio signal.Thus the send out signal could look somethinglike this and it contains all the informationof our original audio signal which can thenbe extracted at the receiver station.So obviously we need some kind of oscillatorcircuit that creates a suitable carrier wavethat we can then modulate with firstly a functiongenerator for testing and afterwards witha microphone circuit.And the first component that came to my mindwhen hearing oscillator was the 555 timerwhich according to my comment section canbe used for pretty much everything, so anAM transmitter should not be a problem.And thus I found two rather popular circuitdesigns for an AM transmitter with it.Like usual the 555 timer creates a squarewave with a specific on and off time and thusfrequency according to these two resistorvalues and this capacitor.The first design however uses the CV or controlvoltage pin to smuggle in our audio signalwhile the second design uses the reset pinfor that.But when we think about the internal structureof such a 555 timer which you can learn allabout by watching my video about the topic,then it should be clear that the audio signalwill not amplitude modulate the carrier wavebut instead only change the on and off timesand thus the frequency.So I almost didn’t feel like trying outthese circuits but since they were so simpleI wanted to give them a try.And after making sure that the carrier signalwas created without a problem, I hooked upmy function generator to firstly the controlvoltage input and saw something like thison the oscilloscope.As suspected, the audio signal does only alterthe frequency overtime and not the amplitude.But just for fun I added a 1m long antennato the output of the circuit and surprisingly,after tuning the radio, the audio signal waspicked up just fine, just listen:Now of course we could also utilize the resetpin of the 555 timer which as you can seeon the oscilloscope creates a similar buta bit worse modulation that can be once againpicked up by the radio.So next I grabbed my small microphone amplifierboard which I created in a previous videoand hooked it up to the 555 timer accordingto this schematic and here is how my transmittedvoice sounds like:As you can hear the audio quality is prettyterrible which means we should probably comeup with a proper AM circuit.The simplest solution I found for this wasthis function generator kit based around theXR2206 IC.You can get such a kit for around 8$ and onits output it can create a sine voltage withan adjustable frequency that is perfect forour AM signal.And to modulate it, all we have to do is tofeed pin 1 of the IC, which is coincidentallycalled amplitude modulating signal input pin,with our audio signal.So I connected the mic amplifier output tothe pin through a 3uF capacitor for decoupling,added the antenna, tuned the frequency to1MHz and selected the channel on the radioand as you can see on the oscilloscope andhear through the radio, the AM transmitterseems to work perfectly fine.And now that we got a functional AM transmitteryou might be asking yourself if that is evenlegal.Well, since there still exist AM stationsaround the world you should definitely checkyour local law.But since my design is pretty low power andthe antenna design it certainly not optimizedat all, we should be just fine.And that brings me to a homemade AM receiverfor which I got myself this TA7642 IC.But finding a proper datasheet for this oldIC was not easy but eventually I found this.It seems like the IC consists of a coupleof transistors which not only amplify ourreceived AM signal but also demodulate it.That means that according to the applicationcircuit, we simply have to build up an LCresonant tank circuit whose resonance frequencyis close to our AM signal and then IC shouldsimply spit out the amplified signal on theoutput.And if you are now wondering what an LC resonanttank circuit is then make sure to watch myvideo about oscillators.But anyway for the homemade coil, I used this10mm thick iron rod around which I firstlyadded a scotch tape barrier to prevent eventualshorts of the enameled copper wire.For that I used this 0.35mm one which I woundaround the rod for approximately 100 turns.After then protecting the coil with anotherlayer of scotch tape, I sanded off a partof the varnish and measured the inductanceof the coil which was around 360uH at 1kHz.So with a capacitance value of 100pF we shouldget a minimum resonance frequency of around840kHz which hopefully should work.So I searched for a suitable trimmer capacitorand of course eventually found one.That means it was time to solder all of therequired components to one another accordingto my slightly modified schematic.As soon as that was done, I powered the circuitwith 2V and connected my oscilloscope to theoutput and as you can clearly see we receivesomething that look awfully similar to ourtransmitted audio signal.But to be certain I had to hook up my recorderto the receiver output and here is the finalresult of my AM experiments.As you can hear my receiver seems to workjust fine with my transmitter which ends myAM adventure for now.Now of course at this point you could hookup an audio amplifier to the receiver to forexample connect headphones and luckily KiWiCojust sent me over one of their crates whichcontains just that.Now in case you do not know, KiWiCo can sendyou monthly crates with DIY kits that aredesigned around STEAM aka Science TechnologyEngineering, Art and Mathematics.They are made not only for kids but prettymuch every age group because let's face it,who doesn't love building something on theirown and understanding how it works along theway.All crates come with everything you need tobuild the project and the best thing is thatyou can have a look in my video descriptionand use the link there KiWiCo.com/GreatScottin order to get a 50% discount on your firstcrate order.And do not worry, they not only ship insidethe USA but to plenty of other countries aroundthe world as well.So feel free to have a look for yourself.And with that being said I hope you enjoyedthis video and I hope I maybe inspired youto try this circuit out on your own becauseit is certainly a fun learning experience.As always thanks for watching, don’t forgetto like, share, subscribe and hit the notificationbell.Stay creative and I will see you next time.