How to Make AM and SW Radio Receiver

Building an AM radio is very easy, on the other hand, if you build an AM radio, you will gain much more knowledge about Analog. Not only that, but behind this little thing there are many formulas and many calculations that you can learn and use for other purposes besides this radio.

LC calculation

MW radio frequency works between 535 kilohertz and 1605 kilohertz in India

We have only one radio station in Kolkata which is Akashvani Maitree 594 khz whose web length is 505 meters.

That's why I took the help of this radio book and here it is clearly written how you can receive the radio.

From this image, you can clearly understand what the frequency looks like when it is in the air and what the signal looks like after receiving it.

LC is the key to receiving the correct signal. L stands for inductor and C stands for capacitor.

To find the frequency of your choice, you need to calculate this formula.

f = 1 / (2π × √(L × C))

Since our frequency is not constant it is variable. so here I am going to use a variable capacitor, This capacitor value is 50 pF to 275 pF.

So now we have the capacitor value and our desired frequency.

Now we just need to find out which inductor is needed

Suppose, my frequency will be 1300 kHz and capacitance will be 50PF then by calculating in this formula our answer will be 0.30 milli henry inductor.

Conversely, if we assume my frequency is 554 kHz and the capacitor is 275 pf then our answer is 0.30 milli henry.

Inductor making process

So now I'm going to make an inductor and I'm going to use the sidebar of an e33 soft core transfer to make the inductor. It's perfect for this job.

here I will use 0.22-millimeter-thin copper wire.

There is a formula for how to make the correct 0.33 inductor.

L = (μ₀μr * π * r²) / length

But if I want to tell it in detail now, it will be long.

I'm just telling you that if you twist 92 times then hopefully you will make 0.30 mh

Oops, I forgot about the  Shortwave radio

For the short wave, you need to twist nine times and the entire coil will produce 0.30 milli henry, and this nine twist will produce two micro henries.

It will be something like this

 if I measure it with an LC meter you will see that it shows 0.30 milli henry but my LC meter can't measure that SW coil low value.

so that's why it showing me this short web coil as just resistance.

I believe everything is correct

LC Experiment

I want to do another experiment to understand everything in a better way

Let's see if it oscillates at the exact frequency if I connect to a transistor with this LC.

That's why I will use a 548 transistor here it is correct for all these tasks

If I can hear a radio station then I can do the next experiments.

Needless to say here. 

All these types of circuits actually act as regenerator oscillators and for this, 

for powering up everything I am going to use this 1.5-volt double A battery

An antenna is of course essential for this circuit.

you need a high impedance headphone. You won't hear it with an amplifier.

because of noise, this headphone coil will act as a low-pass filter.

for powering up everything I am going to use this 1.5-volt double A battery

Anyway, let's see if can i hear any radio stations?

Amazingly our Akashbani Maitri we received. So my hard work has been successful.

Out of curiosity, I want to see on the oscilloscope if it is 594khz?

yes, you can see 594 Khz resonant here.

but the signal is very very weak you can't hear anything without an antenna

Final radio

final Diagram

With that, After so much experimenting now understand how to make a proper radio with very few comments.

So I made a diagram as usual.

If you look closely at this diagram you will see that, here I have used a resistor and capacitor which determine the bios of this transistor.

This is our LC circuit through which we can tune the frequency of our choice

this is the radio band selection switch that I told you about earlier, the full coil is for AM radio and the 9 turns is for SW radio.

The second transistor is the AGF control transistor

Oh sorry it will work as GC control in my case, which will be done by this potentiometer, which I will tell you in detail later.

It is a good practice to create a plan before building something.

So as usual I made a 3D model of my radio so that I don't have any problems while building it.

to do this work I will use a 70/50 mm cupboard dot board.

I'll cut it down the middle just like this,

So that I can use it as my plan.

Now my first step is to properly mount this variable capacitance into this board,

try to keep this variable capacitance as close to your radio circuit as possible

And this variable capacitor is it, also as you can see there is a resistor and a capacitor to set the bios of the transistor.

Most important is, this switch, through which we can select medium wave and short wave.

similarly, I will place the first two transistors inside this copper dot board. I have told you about their work in detail before. 

this gain control potentiometer is very important, Which I'll tell you a little later,

this is the last output transistor, through which we get an Audible voice

hear see,  These two diodes will keep the emf of the inductor within limits If you are using a 3.7 volt battery

It took me about three hours to build this radio circuit, it may take more time for you but if you are patient you can build it.

I made a 3D-printed wheel for this variable capacitor, with which I can easily tune the radio.

Needless to say, Never tune variable capacitors by hand. Then you may not be able to tune the correct channel

In another cooper board, I have built another circuit which is an audio amplifier circuit.

  Hope there is nothing special to show about it.

And I used LM386 IC to make it

A special feature of this circuit is that it can easily fit together nicely and that way I designed it in a 3D model.

in this empty space will sit our AM coil, so I have to install it as usual

When soldering the wire you must remember that the SW and AM radios coil wair

to properly mount it to this board I used a 3D printed structure you can print out if you want.

So finally my radio circuit is complete and looks exactly the way I wanted it to look.

 So now I need a speaker through which I can hear the sound,

I created another 3D model for the exact sound of the speaker,

After printing all night my speaker box was ready in the morning. You have to take out the support material inside it because I don't need any support material here.

After mounting my speaker it looks pretty good,

So anyway let's check our radio physically,

to run this radio I will use a 3.7-volt lithium battery here.

This noise is caused by high gain, and it is controlled by AGC, which means automatic gain control, but in my case, there is no AGC, which is limited to gain control only.

And this GC I can control only by turning this potentiometer. see

Once you get the GC tuned correctly you should have no problem listening to the radio

now if I connect the antenna, you can see a significant change in the sound

Use a 5 feet piece of wire as the antenna for very good results

Here I am getting only one radio station because we have only one AM radio station in India.

Anyway AM radio station is doing very well but now we will see how well short web radio is doing,

An antenna is very important for short web,

Now I am getting some radio stations but they are not worth listening to at all because short web radio stations are not available in India.

And those I am receiving will be from other countries radio stations 

And remember that analog is the first chapter of electronics.

I think this is for a practical Radio AM.

that you can use every day,

You can also make it your study field from which you will gain a lot of knowledge.

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you can watch this video for more information