# How Radio Waves Act - PowerPoint PPT Presentation

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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 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)

### 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

### 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