Simplest AM radio receiver

yes

So basically i need an antenna, a LC circuit that resonates at the required frequency, a diode (can i use any rectifier diode?), a opamp and earphones?

Yes that is all you need.
If you wind the coil on a ferrite rod, you can tune the radio by sliding the rod in and out of the coil.

Okay, so how can i calculate the number of turns i need to wind round the core?

so in the lc circuit i can either keep a variable cap or a variable inductor?

One over two Pi root LC gives you the resonant frequency. (sing it)

The number of turns depends on a lot of things like the diameter.
If you just want to try for medium wave wind 40 turns.
Make the C about 200pF.

can i used a fixed 200uh inductor and just vary the cap? of does it have to be the inductor.

Thanks again

adilmalik:
so in the lc circuit i can either keep a variable cap or a variable inductor?

Yes!
Most car radios used to use a variable inductor, less subject to drift vs. temperature compared to a variable capacitor.

Okay i think i understand now. So the resonant frequency of my LC circuit should cover the AM range?

This shows you step by step from just household items.

(can i use any rectifier diode?

You can but will be able to pick up more stations if you use a germanium diode in place of a rectifying silicon one.

So the resonant frequency of my LC circuit should cover the AM range?

Yes

thank you again, i finally understand this. 1 more question please, now i know that LC circuits are used during reception of Am but are they also used to transmit RF? example: if i transmit a blank carrier wave and connect it to a LC circuit?

but are they also used to transmit RF

They can be if they are part of the oscillator that generates the carrier.
If you have something like a crystal oscillator then you don't need them.

What makes me think GM is in his element with this old technology ?

No offence Mike, I'm one of your biggest fans really.

Crystal sets were old technology when I was a lad. :slight_smile:

I used to sell crystal sets to people when I was at school. That is where I came up with the ferrite rod tuning method, it was a cost down on the variable capacitor. I made the boxes out of cardboard and used to sell then for three and six ( 3/6 ) and it cost me about two shillings to make. Not sure what that is in new money.

17.5p and 10p. Buys b*gger all these days. I'll bet there's an amateur radio ticket in your past somewhere......

Grumpy_Mike:
One over two Pi root LC gives you the resonant frequency. (sing it)

When nobody else is listening preferably... my landlady just gave me a O___o look as though I'm an escaped mental patient :wink:

I'll bet there's an amateur radio ticket in your past somewhere.

G8HBR

my landlady just gave me a O___o look

:slight_smile:

just got all the parts and made a Am radio. it worked! i used a 100pf cap and a inductor like you told me and tuned it using the rod method!

Well done, I bet you are well happy.
Can you pick up many stations?

i am as very very happy! thank you again! i thought id never understand how a LC circuit works but i do now! i can easily pick up 3 stations, but i used an op amp to amplify the signal, also the signal is also sometimes very noisy, how can i reduce this? capacitor?