How Radio Waves Travel
Scientific Notation
1,000,000,000
1,000,000
1,000
1
.01
.001
.000001
.00000001
.000000000001
=
=
=
=
=
=
=
=
=
1 X 109
1 X 106
1 X 103
1 X 100
1 X 10-2
1 X 10-3
1 X 10-6
1 X 10-9
1 X 10-12
GIGA (G)
MEGA (M)
KILO (k)
UNIT
CENTI ( c )
MILLI (m)
MICRO (µ)
NANO (n)
PICO (p)
Note: Bold may be on license exam.
Examples:
• 14 MHz = 14,000,000 Hertz
• 2mV
= 0.002 Volts
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How Radio Waves Travel
Frequency

Frequency is the number of AC cycles/second.

Hertz (Hz) is the unit for cycles per second.

60 Hz is 60 cycles per second.



146MHz is 146,000,000 cycles per second
Audio Frequencies (AF) = 20 Hz to 20,000 Hz.

Communication voice is 300 to 3,000 Hz. (~ 3 KHz.)

300 Hz is a low, deep sound of a man’s voice

3000 Hz is a very shrill sound
Radio frequencies (RF) over 20,000 Hz.

High Frequency (HF) 3 to 30 MHz

Very High Frequency (VHF) 30 to 300 MHz

Ultra High Frequency (UHF) 300 to 3000 MHz
Electromagnetic


waves travel @ speed of light.
Distance a radio wave travels in 1 cycle is its wavelength
Wavelength = (Speed of Light) / (Frequency)

Example: 14MHz = 14,000,000 Hz. Its wavelength is
(3*108 meters per second) / (14,000,000 Hz) = about 20 meters
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How Radio Waves Travel
Radio Spectrum
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Radio M.B Req. 2a-1
How Radio Waves Travel
VHF and UHF Propagation

All radio signals travel out to the horizon, just
like light, if they are not refracted (bent) or
reflected.

VHF and UHF signals are usually not refracted or
reflected. So, if they are most useful for talking
to stations that you can see.

But, occasionally, obstacles can refract a tiny bit
of signal and it can still be received:
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Radio M.B Req. 2a-1
How Radio Waves Travel
VHF and UHF Propagation

VHF and UHF waves can also reflect
(bounce) off of large metal objects like
airplanes or metal buildings.


VHF waves can also bounce off of meteors




Signals could be strong or weak
UHF Frequencies are usually to high to bounce off of
meteors
Lower VHF frequencies, such as the 6 meter ham band
(50 MHz) work best
Communication does not last long. When the meteor
disappears from sight, communication disappears soon
afterwards
Sometimes humidity and thunderstorms will
scatter VHF and UHF a little bit and
communication of several hundred miles is
possible
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Radio M.B Req. 2a-1
How Radio Waves Travel
HF Propagation

HF signals can bounce off of an area of the
atmosphere called the ionosphere

Communication for thousands of miles is
possible
The ionosphere is between 60 and 250 miles
about the surface of the earth
When the weather in the ionosphere is severe,
HF radio waves can easily bounce off of it





Sometimes they can bounce between the earth and the
ionosphere several times and worldwide communication
is possible
The weather in the ionosphere is the most severe when
there are many spots on the sun.
The number of sunspots vary daily and, in general, in an
11 year cycle. This is similar to seasons (spring,
summer, fall, and winter) on earth. But, sun activity can
vary greatly on a day to day basis.
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Radio M.B Req. 2a-1