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##### May 07, 2012, 02:21 pm
I'm trying to understand how am radios work. But i dont understand the most basic and fundamental parts required for reception of am radio. can some one help me out by telling me how to make the simplest AM receiver and please explain LC circuits.

Thanks!

#### Erni

#1

#2
##### May 07, 2012, 02:25 pm
i just saw the circuit shown in wiki, can i feed the audio output to a op amp instead of using crystal earphones?

#### RandallR

#3
yes

#4
##### May 07, 2012, 02:29 pm
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?

#### Grumpy_Mike

#5
##### May 07, 2012, 02:36 pm
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.

#6
##### May 07, 2012, 02:37 pm
Okay, so how can i calculate the number of turns i need to wind round the core?

#7
##### May 07, 2012, 02:40 pm
so in the lc circuit i can either keep a variable cap or a variable inductor?

#### Grumpy_Mike

#8
##### May 07, 2012, 02:42 pm
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.

#9
##### May 07, 2012, 02:43 pm
can i used a fixed 200uh inductor and just vary the cap? of does it have to be the inductor.

Thanks again

#### Runaway Pancake

#10
##### May 07, 2012, 02:44 pm

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.
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

#11
##### May 07, 2012, 02:48 pm
Okay i think i understand now. So the resonant frequency of my LC circuit should cover the AM range?

#### Grumpy_Mike

#12
##### May 07, 2012, 02:50 pm
This shows you step by step from just household items.

Quote
(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.

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

Yes

#13
##### May 07, 2012, 02:56 pm
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?

#### Grumpy_Mike

#14
##### May 07, 2012, 03:16 pm
Quote
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.

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