Transcript Signals and Waves

Radio Waves and Signals
Week 4
We imagine radio signals/waves
travel as sine waves.
The ripple of these waves are started by
the vibration of an electron
The signal is produced in the
circuits of the radio, once
the vibration leaves the
radio through the
antenna it becomes
a radio wave.
Radio waves are just one part
of the electromagnetic spectrum
An electromagnetic wave consists
of a vibrating
electric field
and a
vibrating
magnetic
field.
It is the electromagnetic wave
that carries the radio signal
between the
transmitting
and
receiving
stations
.
The EM wave oscillates in such a way to
mimic the signal that generated the wave.
A cycle is one complete vibration.
This diagram actually shows 3 cycles.
Wavelength (l) is the distance the wave
travels in 1 complete cycle
The number of vibrations per second
is the frequency.
1
s
e
c
o
n
d
What is the
frequency of
each wave?
2 Hz
10 Hz
Frequency is measured in Hertz (Hz):
1 vibration/sec is 1 Hz
AM stations broadcast in kilohertz (kHz)
1330 KVOL broadcasts at 1,330,000 Hz
FM stations broadcasts in megahertz (MHz)
96.5 KPEL broadcasts at 96,500,000 Hz
Test Question Alert!
What type of wave carries radio
signals between transmitting
and receiving stations?
Electromagnetic
Test Question Alert!
What is the name for the distance
a radio wave travels during
1 complete cycle?
Wavelength
Test Question Alert!
What term describes the
number of times per second
that an alternating current
reverses direction.
frequency
In what unit is frequency measured?
Hertz
1 vibration(s) per _____
1 second(s)
A Hertz is ____
Test Question Alert!
What are the two components of a
radio wave? (or any other wave in the
electromagnetic
spectrum)
Electric and
magnetic fields
All radio waves travel at the speed
of light (c) through a particular type
of medium.
The speed of light through
space is 300,000,000 m/s
Since all radio waves travel at the speed of light
no matter what their frequency happens to be
the following is true:
When length increases
then frequency decreases
or
when length decreases
then frequency increases.
Radio waves can be referred to by
wavelength or frequency because
the two are related by the speed of light.
c
f
l
A wave with a length of 2 m means
it has a frequency of 150,000,000 Hz
because
300,000,000 / 150,000,000 = 2
This frequency typically would be referred to as
150 MHz
The formula for converting frequency to wavelength in meters is :
Wavelength in meters = 300 divided by frequency in megahertz.
300
f in
l
MHz in m
To convert frequency to wavelength in
meters divide 300 by frequency in MHz.
96.5 KPEL broadcasts at 96.5 MHz so the
length of the waves is 300/96.5. The waves
are approximately 3 meters in length.
What property does wavelength refer to?
The distance a wave travels during
1 complete cycle.
How fast does a radio wave travel?
(Two acceptable ways to answer)
Speed of light
or
300,000,000 meters/second
Describe the relationship between
wavelength and frequency.
inverse
wavelength
frequency
or
wavelength
frequency
What is the formula for converting
frequency into wave length (in meters)?
300 / Mhz
Approximate wavelengths are often used to
identify the different frequency bands.
All types of radio frequency signals are
referred to by the abbreviation RF, but for
convenience the entire range is spilt into
sub-ranges.
3000 MHZ
Communications at VHF and UHF
are generally “line of sight” communications.
That is they travel directly from the
transmitting station to the receiving
station.
Normally used for local communication.
Direct (not via a repeater) UHF signals are
rarely heard from stations outside your
local coverage area because UHF signals
are not reflected by the ionosphere.
The radio horizon is the distance at which radio
signals between two point are blocked by the
curvature of the Earth.
The radio horizon is somewhat farther than the
visual horizon because the earth seems less
curved to radio waves than light waves.
When using a hand-held transceiver
inside a building you might want to
choose to operate in a UHF band.
UHF signals are often more
effective from inside buildings than
VHF signals because the shorter
wavelength allows them to more
easily penetrate the structure of
buildings.
Knife-edge propagation is the term used to describe when
signals are partially refracted around solid objects
exhibiting sharp edges.
You might be able to use this phenomenon
to get your signal around a building in an
urban setting.
What is the name assigned to each
of these frequency ranges?
3 – 30 MHz
30 – 300 MHZ
300 – 3000 MHz
Why are UHF frequencies usually
limited to local communications?
UHF signals are not reflected
by the ionosphere.
What do we call the distance at which
radio signals are blocked by the curvature
of the Earth?
Radio Horizon
Why is the radio horizon somewhat
farther that the visual line of sight
distance between two stations?
The earth seems less curved
to radio waves than to
light waves.
Why should you choose to use
frequencies in the UHF band when using
a hand-held receiver inside a building?
The shorter waves length allows them to
more easily penetrate the structure of
the building.
What do we call the phenomenon in which
signals are partially refracted (bent) around
solid objects with sharp edges?
Knife-edge propagation