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# How Radio Waves Act - PowerPoint PPT Presentation

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

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Presentation Transcript

Similar to Book Chapter 2 – sections 2.4 and 2.6

• 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
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
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
• 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)
• 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)
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)
• 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
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