# Electromagnetic radiation production and detection

Discussion in 'General Electronics Discussion' started by xeroshady, Oct 7, 2012.

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Oct 5, 2012
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:

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2. ### davennModerator

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Sep 5, 2009

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

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

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

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

Last edited: Oct 7, 2012

5
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Oct 5, 2012
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?

4. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
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

5. ### davennModerator

13,866
1,958
Sep 5, 2009
no it isnt, its just a tuned circuit, it needs excitation by an AC signal ( oscillator) with the same resonant frequency

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

cheers
Dave

6. ### duke37

5,364
772
Jan 9, 2011
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.

7. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
652
May 8, 2012
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

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