1 / 10

How Radio Waves Act

How Radio Waves Act. Similar to Book Chapter 2 – sections 2.4 and 2.6. Lets Start with. Radio Waves are fast They go 300,000,000 meters every second – (The Speed of Light) (T4B05) A meter is a little more than 3 feet – its about 39 inches

lucas
Télécharger la présentation

How Radio Waves Act

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. How Radio Waves Act Similar to Book Chapter 2 – sections 2.4 and 2.6

  2. Lets Start with • Radio Waves are fast • They go 300,000,000 meters every second – (The Speed of Light) (T4B05) • A meter is a little more than 3 feet – its about 39 inches • Geeky science type people usually like using the metric system with meters instead of feet to measure distance

  3. Electro-Magnetic Waves • Sort of like invisible ripples on a pond of water • The number of times the wave (or electricity) goes up and down in a second is the frequency (T4B02) • If the wave goes up and down (oscillates) more than 20,000 times a second it is called a Radio Wave (T4B04) • We call an up and down a hertz – so we measure frequency in hertz (T4A05) • Electricity in your wall plug goes up and down 60 times a second or 60 hertz – 60 Hertz means 60 cycles per second (T4B03) • Sound Waves go up and down – 300 to 3000 Hertz is called Voice Frequencies (T4B08) • Radio waves that Amateurs use to send messages go up and down millions of times every second • We add Mega in front of hertz to mean a million

  4. The String Analogy • Suppose you have a long piece of string – 300,000,000 meters long • If you cut the string into a whole bunch of little pieces how long will they be? • They would be short • If you cut the string into just a few pieces – how long will the pieces be? • They will be long

  5. Applied to Radio Waves • The length a radio wave travels while going up and down is called the wavelength • If the wavelength gets shorter then there must be more pieces of our string • As the wavelength get shorter the frequency increases (T4B06) • There is even a formula Wavelength = 300/ Frequency (T4B07)

  6. We Can Describe a Radio Wave by it’s Frequency or Wavelength • We often describe the different “bands” that Amateur Radio uses by The Physical Length of the Wave (T4B09) • Three Most Popular Amateur Radio Waves for sending messages are • 6 meters (50 to 54 megahertz – means the wave goes up and down 50 million to 54 million times every second • 2 meters [the one we use for the church] (144 to 148 megahertz – means the wave goes up and down 144 million to 148 million times every second) • 70 centimeters {centi means we chop one meter up into 100 little pieces} (420 to 450 megahertz – means the wave goes up and down 420 million to 450 million times every second)

  7. The Frequencies We Use Most • Over 30,000,000 Hertz (30 Megahertz) called VHF (Very High Frequency) • Yes this is also frequency range for TV signals – your VHF channels • Over 300,000,000 Hertz (300 Megahertz) called UHF (Ultra High Frequency) • These signals travel fairly straight line (line of sight) • Radio Horizon is where curvature of Earth Blocks the signals (T9B04) • Usually about 1/3rd further than you can see because VHF/UHF bend a little and earth seems less curved(T9B11)

  8. Long Distance Radio Waves • Radio waves that go around the world bounce of ionized layers in the atmosphere (ionosphere) • VHF and UHF don’t bounce – (can be nice to talk to satellites or space stations) • 50 to 60 miles easy – taller tower I have got to Southern Tennessee • VHF and UHF not usually heard for very long distances because they don’t bounce off the ionosphere (T9B01) • Sometimes VHF (especially 6 meters) go long distances • Around here especially common to go to South America • Get sporadic E reflection (T9B02) • E layer is the lowest ionized layer in the Ionosphere

  9. Dealing With Signal Blocks • Trees and Buildings can block signals – VHF/UHF travel bent lines of sight • When traveling signal may flutter clear and faded – called Picket Fencing (T9B10) • If someone tells you you were clear a minute ago and now they can hardly hear you try moving a few feet (T9B05) • Random reflections off of objects can do things • With our practice radio sessions we have had people move the car in the driveway and be heard or not heard

  10. Blasting Radio Waves Through Buildings • Shorter wavelengths cut through things better than longer waves • Example X-rays are very very short electromagnetic waves • We can’t X-ray into buildings but UHF will often work better in buildings • Common doing hospital emergency communications with 70 centimeters instead of 2 meters • Shorter wavelength of UHF allows the waves to more easily penetrate urban areas and buildings (T9B06) • The trade off is they are don’t have as much long range

More Related