Electromagnetic radiation production and detection

[xeroshady]

Hey guys, I'm working on a physics project about the study of electromagnetic waves including their production and detection. I need help with the electronics part.

My questions regarding the production:

1) Will just a tank circuit be enough to produce electromagnetic waves, propagated through an antenna?

2)How do I supply power to charge the capacitor? (where do I connect a voltage source?)
And do I need a constant power supply or provide feedback to the circuit?

3) Where do I connect the antenna?

Regarding detection:

I'm pretty clueless about this one. I want something to happen, like an LED to glow, when the receiver circuit receives the radiation and resonates. How should I go about this?

 

[davenn]

Hi xeroshady

Hey guys, I'm working on a physics project about the study of electromagnetic waves including their production and detection. I need help with the electronics part.

My questions regarding the production:

1) Will just a tank circuit be enough to produce electromagnetic waves, propagated through an antenna?

Yes, but with 5V and just switching a switch on and off it will produce only very small pulses

2)How do I supply power to charge the capacitor? (where do I connect a voltage source?)
And do I need a constant power supply or provide feedback to the circuit?

the way you have drawn it is sorta ok .... the thing is, that tank cct of the cap and inductor will have a resonant freq. You need to use an online calculator to determine that freq.
Just switching the switch on and off periodically will not produce a freq that will excite that tank cct. tho providing pulses of power will cause the circuit to brieflt oscillate at its resonant freq. The output will be VERY low
The way that is usually done is to have the tank circuit as
1) part of an oscillator running at that resonant freq or
2) have an oscillator of that appropriate freq driving that tank circuit

3) Where do I connect the antenna?

where it is would be OK , but you need to take the previous comments into account

Regarding detection:

I'm pretty clueless about this one. I want something to happen, like an LED to glow, when the receiver circuit receives the radiation and resonates. How should I go about this?

Thats going to take much more work. initially you need to get a transmitter going on a freq that is allowable in your country for unlicenced experimenting. Then you can work on a receiver..
2 ways to make a LED glow with a received signal
1) have the LED at the centre of a dipole antenna resonant to the freq of the transmitter
.... this will work over VERY short range a few centimetres
2) have a complete receiver whose output will operate a LED driver circuit

cheers
Dave

 

[xeroshady]

Sorry, I don't really get it. I get that the voltage source will only make the tank circuit produce pulses. But isn't the tank circuit (L and C) itself an oscillator? When you said that I need to include the tank circuit in the oscillator circuit, did you mean something like include it in Colpitt's oscillator circuit?

 

[CDRIVE]

Sorry, I don't really get it. I get that the voltage source will only make the tank circuit produce pulses. But isn't the tank circuit (L and C) itself an oscillator?

No, not in this world. What you're describing is "over unity" also known as "perpetual motion". Neither of which exists in this dimension.

Chris

 

[davenn]

Sorry, I don't really get it. I get that the voltage source will only make the tank circuit produce pulses.
But isn't the tank circuit (L and C) itself an oscillator?

no it isnt, its just a tuned circuit, it needs excitation by an AC signal ( oscillator) with the same resonant frequency

When you said that I need to include the tank circuit in the oscillator circuit, did you mean something like include it in Colpitt's oscillator circuit?

yes, it can be the tuned circuit within a colpitts oscillator and it will then set the freq of oscillation

here's a nice page with a java animation of a LC Colpitts oscillator

http://www.falstad.com/circuit/e-colpitts.html

cheers
Dave

 

[duke37]

If you give a kick to a tuned circuit, it will oscillate and the oscillation will decrease as energy is lost. If more energy is put into the circuit than is lost, the amplitude will rise until there is a balance between energy in and energy out. This is an oscillator.

There are many circuits to make oscillators, often frequency stability is important, sometimes amplitude stability, sometimes the ability to modulate the strength or the frequency.

If a tuned circuit is driven with a frequency from another source, it is not an oscillator but an amplifier.

 

[CDRIVE]

If you give a kick to a tuned circuit, it will oscillate and the oscillation will decrease as energy is lost.

This is what duke is describing to you. Think of it as being analogous to striking a tuning fork. They don't resonate forever either.

Chris