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| Nikita |
 Posted: Wed Nov 04, 2009 3:02 pm Post subject: Variable capacitor and Crystal radio (Newbie to wiring) |
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New Member
Joined: 04 Nov 2009
Posts: 1
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Hello, I admit that I don't have much understanding of anything but the simplest circuits, but could you help me here?
I am trying to build an AM radio from scratch. I guess it's a good way to learn more about electronics. Here is my plan:
I know I'm missing something. This should let me select a station by adjusting capacitance in an LC circuit. But, the signal is still modulate it. To demodulate it, I apparently need a second capacitor there somewhere. And I have no idea how should that one part work.
1) Where should I place a capacitor?
2) How should I pick it's capacitance?
3) Is there anything horribly wrong with this schematic?
Also, I've had some trouble finding a variable capacitor, so I decided to make one myself, with aluminium foil! ... Is that even possible?..
What I need is, a capacitor that can vary from 100 micro farads to 0.
All I have is some aluminium foil, enough wires, and 3 normal capacitors: 1000, 47, and 10 micro farads. Perhaps there is a circuit to make a normal one into adjustable?
I'd try to do it with aluminium, but I can't come up with calculations. From what I see, if it's flat plate conductor, even a whole square meter of aluminum would have to be placed at a fraction of a micrometer away from each other. That just can't be right.
So guys, please answer my questions and don't be harsh on me, I'm just beginning to study electronics. |
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| Leszek Luchowski |
| Posted: Thu Nov 05, 2009 12:01 pm Post subject: |
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Forum Ph.D.
Joined: 16 Jun 2008
Posts: 647
Location: Gliwice, Poland
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1) and 2) : you don't really need one. The diode plus the inertia of your headphones will do your demodulation for you.
3) : yes, there is one serious error: it doesn't make sense to have a circuit consisting of two parts that are only connected at one point. And your circuit is just that, the single connection being the diode. I suggest connecting the emitter of your transistor to the ground point of the oscillator.
You will also most probably need a resistor between the "+" of your battery and the base of the transistor.
I am sure you can find a lot of ready schematics on the Web.
Good luck - Leszek.
_________________
Leszek. Pronounced [LEH-sheck]. The wondering Slav.
History teaches us that we don't learn from history. |
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| Peter |
| Posted: Thu Dec 31, 2009 7:44 am Post subject: |
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New Member
Joined: 29 Dec 2009
Posts: 2
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It's my variant crystal receiver. It's "reciver for direct amplifier". Very simple circuit.
Click on the image to view it at its original size |
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