Wednesday, February 27, 2013

Lesson 1- Radio Waves

Today's world is full of radio waves. Just looking at where I am sitting, I see a tablet, smart phone, printer, wireless router,  laptop, coordless phone, GPS receiver, key fob, and bluetooth adapter, all of which are radios. How do these radios work?

First of all, let me explain about something called Electromagnetic Radiation. Essentially, this is waves of electricity and magnetism moving in a usually straight direction. There is a lot more that could be said on this matter, but the key thing for now is that the electric waves are in one plane, and the magnetic waves move perpendicular to the electric waves. The following picture from Wikipedia shows this. It's a bit tricky to see, but the blue lines (Electric) are vertical, and the red lines (Magnetic) are horizontal. The wave itself moves in one direction, perpendicular to both. See also this illustration. I won't talk about it much now, but the orientation of the electric wave is called the polarization. In this case, the wave is vertically polarized.

There are a ton of types of electromagnetic radiation, including radio waves, microwaves, infrared, light, ultraviolet, and x-rays. All of these are fundamentally the same. So, what sets a radio wave apart from an x-ray? The key factors are wavelength and frequency. Wikipedia provides us with this handy chart of the various forms of electromagnetic radiation

 Wavelengths of various forms of Electromagnetic Radiation
As you can notice, the wavelength and the frequency change in opposite directions. In fact, you can always multiply the wavelength and frequency of light together, and get a constant. What is that constant, you might ask? The speed of light. Thus:

c=300,000,000 m/s = wavelength*frequency.

This is probably the signal most important formula to remember when taking the amateur radio exam. There are many questions like: Which frequency is on the 2m band? Simply taking 300,000,000/2m, and you'll have an approximation (150MHz). Eliminate any of the answers that aren't close to this, and you'll be close to (Or have) the right answer. It turns out the 2m band is actually 144-148Mhz, which isn't too far away at all from our guess.

Finally, let me give just a few general pointers about how the different types of light interact. There are exceptions to ever rule, but I'm mostly focusing on radio waves, so...
  • Higher frequency light has more penetrating power. That is why X-rays and Gamma-rays are very dangerous, and visible light is not.
  •  Light can wrap around objects that are smaller, or on the same order of magnitude, as the light is. Essentially, longer wavelengths aren't affected by objects as much as shorter wavelengths. That is the principal reason why you can be in a room with no windows, but you could still listen to the radio, under many circumstances. Very high frequency radio waves would still be blocked as well, but the larger waves would not be blocked as much.
  • Metal tends to block most or all radio waves.

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