How Radio Waves Act

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 its 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 dont 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 dont 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 cant 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 dont have as much long
  range