Download Radio Signals and Fundementals

Chapter 2
Radio Signals &
Fundamentals
System of Metric Units
Tera
T
1012
1,000,000,000,000
Giga
G
109
1,000,000,000
Mega
M
106
1,000,000
Kilo
k
103
1,000
100
1
Basic Unit
1/18/11
Milli
m
10-3
0.001
Micro
μ
10-6
0.000001
Nano
n
10-9
0.000000001
Pico
p
10-12
0.000000000001
HPST Technician Course
2
Units of Measurements
109 106 103 102 101 100 10-1 10-2 10-3 10-6 10-9 10-12
G M k
h da
d
c m
µ
n
p
giga mega kilo hecto deca
deci
centi milli
micro nano pico
Watt
1
Ampere
1
Kilowatt
1000
Milliampere
1/1000
Megawatt
1,000,000
Microampere
1/1,000,000
Gigawatt
1,000,000,000
Nanoampere
1/1,000,000,000
3
T5B01How many milliamperes is 1.5 amperes?
A. 15 milliamperes
B. 150 milliamperes
C. 1500 milliamperes
D. 15000 milliamperes
T5B02What is another way to specify a radio
signal frequency of 1,500,000 Hertz?
A. 1500 kHz
B. 1500 MHz
C. 15 GHz
D. 150 kHz
T5B04How many volts are equal to one microvolt?
A. One-one millionth of a volt
B. One million volts
C. One thousand kilovolts
D. One-one thousandth of a volt
The Basic Radio Station
What Happens During Radio
Communication?
• Transmitting (sending a signal):
• Information (voice, data, video, commands,
etc.) is converted to electronic form.
• The information in electronic form is
attached or embedded on a radio wave (a
carrier).
• The radio wave is sent out from the
station antenna into space.
What Happens During Radio
Communication?
• Receiving end:
• The radio wave (carrier) with the information
is intercepted by the receiving station
antenna.
• The receiver extracts the information from
the radio wave.
• The information is then presented to the user
in a format that can be understood (sound,
picture, words on a computer screen,
response to a command).
What Happens During Radio
Communication?
• This sounds pretty simple, but it in reality is
pretty complex.
• This complexity is one thing that makes ham
radio fun…learning all about how radios work.
• Don’t be intimidated. You will be required to
only know the basics, but you can learn as
much about the “art and science” of radio
as you want.
Radio Waves are AC
• Radio waves (electromagnetic radiation) are
AC waves.
• Radio waves are used to carry the information
you want to convey to someone else.
Wave Vocabulary
• Before we study radio
waves, we need to learn
some wave vocabulary.
•
•
•
•
•
Amplitude
Frequency
Period
Wavelength
Harmonics
How Radio Waves Travel
•
•
•
Moving electrons in the antenna create a
magnetic field.
This changing magnetic field creates an
electric field.
Then back and forth between magnetic
and electric fields from point A to point B.
Finding Where You are
on the Radio Dial
• There are two ways to tell someone where
to meet you on the radio dial (spectrum).
• Frequency
• Band
Radio Frequency (RF) Spectrum
• The RF spectrum is the range of wave
frequencies which will leave an antenna
and travel through space.
• The RF spectrum is divided into segments
of frequencies that basically have unique
behavior.
Radio Frequency (RF) Spectrum
Radio Frequency (RF) Spectrum
Wavelength
• The distance a
radio wave travels
during one cycle.
• One complete
change between
magnetic and
electric fields.
Wavelength
300
fMHz λm
Frequency (MHz) = 300 / Wavelength (meters)
Wavelength (meters) = 300 / Frequency (MHz)
T3B01 -- What is the name for the distance a
radio wave travels during one complete cycle?
A.
B.
C.
D.
Wave speed
Waveform
Wavelength
Wave spread
T3B04 -- How fast does a radio wave travel
through free space?
A. At the speed of light
B. At the speed of sound
C. Its speed is inversely proportional to its
wavelength
D. Its speed increases as the frequency
increases
T3B05 -- How does the wavelength of a radio
wave relate to its frequency?
A. The wavelength gets longer as the frequency
increases
B. The wavelength gets shorter as the frequency
increases
C. There is no relationship between wavelength
and frequency
D. The wavelength depends on the bandwidth
of the signal
T3B06 -- What is the formula for converting
frequency to wavelength in meters?
A. Wavelength in meters equals frequency in
hertz multiplied by 300
B. Wavelength in meters equals frequency in
hertz divided by 300
C. Wavelength in meters equals frequency in
megahertz divided by 300
D. Wavelength in meters equals 300 divided
by frequency in megahertz
T3B07 -- What property of radio waves is often
used to identify the different frequency bands?
A.
B.
C.
D.
The approximate wavelength
The magnetic intensity of waves
The time it takes for waves to travel one mile
The voltage standing wave ratio of waves
T3B08 -- What are the frequency limits of the
VHF spectrum?
A.
B.
C
D.
30 to 300 kHz
30 to 300 MHz
300 to 3000 kHz
300 to 3000 MHz
T3B09 -- What are the frequency limits of the
UHF spectrum?
A.
B.
C
D.
30 to 300 kHz
30 to 300 MHz
300 to 3000 kHz
300 to 3000 MHz
T3B10 -- What frequency range is referred to as
HF?
A.
B.
C.
D.
300 to 3000 MHz
30 to 300 MHz
3 to 30 MHz
300 to 3000 kHz
T3B11 -- What is the approximate velocity of a
radio wave as it travels through free space?
A.
B.
C.
D.
3000 kilometers per second
300,000,000 meters per second
300,000 miles per hour
186,000 miles per hour
T5A12 -- What term describes the number of
times per second that an alternating current
reverses direction?
A. Pulse rate
B. Speed
C. Wavelength
D. Frequency
T5C05 -- What is the unit of frequency?
A.
B.
C.
D.
Hertz
Henry
Farad
Tesla
T5C06 -- What does the abbreviation “RF” refer
to?
A. Radio frequency signals of all types
B. The resonant frequency of a tuned circuit
C. The real frequency transmitted as opposed to
the apparent frequency
D. Reflective force in antenna transmission lines
Break
So, Where Am I?
• Bands identify the segment of the
spectrum where you will operate.
• Wavelength is used to identify the band.
• Frequencies identify specifically where you
are within the band.
Another Use for Frequency and
Wavelength
• For the station antenna to efficiently send the
radio wave out into space, the antenna must be
designed for the specific operating frequency.
• The antenna length needs to closely match the wavelength of
the frequency to be used.
• Any mismatch between antenna length and frequency
wavelength will result in radio frequency energy being reflected
back to the transmitter, not radiated into space.
Adding Information - Modulation
• When we imprint some information on the
radio wave, we modulate the wave.
• Turn the wave on and off
• Voice -- AM and FM
• Data
• Different modulation techniques are called
modes.
CW - Morse Code – On and Off
Amplitude Modulation (AM)
• In AM, the amplitude
of the carrier wave is
modified in step with
the waveform of the
information (voice).
Characteristics of AM
• AM signals consist of three
components:
• Carrier
• Lower sideband
• Upper sideband
• Voice bandwidth is from
300 Hz to 3,000 Hz.
• AM bandwidth is twice the
voice bandwidth.
Characteristics of AM
• Sound waves that make
up your voice are a
complex mixture of
multiple frequencies.
• When this complex
mixture is embedded on
a carrier, two sidebands
are created that are
mirror images.
Characteristics of AM
50%
25%
25%
Single Sideband Modulation (SSB)
• Since voice is made up of
identical mirror image
sidebands:
• We can improve efficiency
of transmission by
transmitting only one
sideband and then
reconstruct the missing
sideband at the receiver.
AM and SSB
An unmodulated RF
carrier requires narrow
bandwidth
Modulation of the carrier
creates sidebands. This
requires more bandwidth.
Transmitter power is spread
across this bandwidth
AM and SSB
The carrier contains no
audio information.
The sidebands contain
duplicate audio information
By filtering out the carrier and one sideband, we
save spectrum and concentrate our RF energy
into a narrower bandwidth.
SSB is therefore more efficient.
AM and SSB
 When AM is not modulated (when you are not
talking), the transmitter remains at full power
 When SSB is not modulated the transmitter output
power drops to almost nothing.
 When either AM or SSB is over-modulated the signal
may cause “splatter,” and interfere with other stations.
 The process of extracting speech or music from an
AM or SSB signal is called detection
Frequency Modulation
 Frequency varies in proportion to the modulating signal
 Amount frequency varies when modulated is called deviation
 FM transmitters operate at full power at all times, even when you are
not talking.
 When over-modulated, the signal can be so wide (bandwidth) it may
interfere with adjacent channels. This is called over-deviation.
 Speaking louder into the microphone may cause over-deviation
 Eliminate by moving the microphone away from your mouth or
speaking more softly
Frequency Modulation
• FM signals have one carrier and several sidebands
• 5-15 kHz wide
• Amplitude doesn’t change, same power all the time
 Limiter circuit strips away all amplitude variations,
including noise
 Compare AM radio to FM Radio
• Static
• Engine noise
• Lightning
Frequency Modulation (FM)
• Instead of varying amplitude, if
we vary the frequency in step
with the information waveform,
FM is produced.
• FM signals are much more
resistant to the effects of noise
but require more bandwidth.
• FM bandwidth (for voice) is
between 5 and 15 kHz.
Phase Modulation
 Very similar to frequency modulation
 In FM, the frequency of the signal is varied
 In phase modulation (PM), the phase of the signal is
varied
 Both modes received with the same circuitry
 Most hams don’t know whether their “FM”
transceiver is really FM or PM
AM vs. SSB
 AM
 Sounds really nice
 Inexpensive
 Simpler equipment
 Uses a lot of
bandwidth
• SSB
• More efficient.
• Further range based on
same output power.
• Narrower bandwidth,
more room on
crowded bands.
• All modern HF radios
support SSB
• Most common voice
mode on HF bands
SSB & CW
 SSB uses less bandwidth than FM
 Typically 2-3 kHz vs. 5-15 kHz
 Power concentrated into narrow bandwidth
 Allows communications over longer ranges and under
poor conditions
 Below 10 MHz use LSB (except 60 meters)
 Above 10 MHz use USB
 CW uses even less bandwidth
 150 Hz (Correct table 2-3)
 Best mode for weak signal communications
T1B09 -- Why should you not set your transmit
frequency to be exactly at the edge of an
amateur band or sub-band?
A. To allow for calibration error in the
transmitter frequency display
B. So that modulation sidebands do not extend
beyond the band edge
C. To allow for transmitter frequency drift
D. All of these choices are correct
T2B05 -- What determines the amount of
deviation of an FM (as opposed to PM) signal?
A. Both the frequency and amplitude of the
modulating signal
B. The frequency of the modulating signal
C. The amplitude of the modulating signal
D. The relative phase of the modulating signal
and the carrier
T2B07 -- What could cause your FM signal to
interfere with stations on nearby frequencies?
A. Microphone gain too high, causing over-
deviation
B. SWR too high
C. Incorrect CTCSS Tone
D. All of these choices are correct
T2B06 -- What happens when the deviation of an
FM transmitter is increased?
A.
B.
C.
D.
Its signal occupies more bandwidth
Its output power increases
Its output power and bandwidth increases
Asymmetric modulation occurs
T8A01 -- Which of the following is a form of
amplitude modulation?
A.
B.
C.
D.
Spread-spectrum
Packet radio
Single sideband
Phase shift keying
T8A02 -- What type of modulation is most
commonly used for VHF packet radio
transmission?
A.
B.
C.
D.
FM
SSB
AM
Spread Spectrum
T8A03 -- Which type of voice mode is most often
used for long-distance (weak signal) contacts on
the VHF and UHF bands?
A.
B.
C.
D.
FM
AM
SSB
PM
T8A04 -- Which type of modulation is most
commonly used for VHF and UHF voice
repeaters?
A.
B.
C.
D.
AM
SSB
PSK
FM
T8A05 -- Which of the following types of emission
has the narrowest bandwidth?
A.
B.
C.
D.
FM voice
SSB voice
CW
Slow-scan TV
T8A06 -- Which sideband is normally used for 10
meter HF, VHF and UHF single-sideband
communications?
A.
B.
C.
D.
Upper sideband
Lower sideband
Suppressed sideband
Inverted sideband
T8A07 -- What is the primary advantage of single
sideband over FM for voice transmissions?
A. SSB signals are easier to tune
B. SSB signals are less susceptible to
interference
C. SSB signals have narrower bandwidth
D. All of the choices are correct
T8A08 -- What is the approximate bandwidth of a
single sideband voice signal?
A.
B.
C.
D.
1 kHz
3 kHz
6 kHz
15 kHz
T8A09 -- What is the approximate bandwidth of a
VHF repeater FM phone signal?
A.
B.
C.
D.
Less than 500 Hz
About 150 kHz
Between 10 and 15 kHz
Between 50 and 125 kHz
T8A10 -- What is the typical bandwidth of analog
fast-scan TV transmissions on the 70 cm band?
A.
B.
C.
D.
More than 10 MHz
About 6 MHz
About 3 MHz
About 1 MHz
T8A11 -- What is the approximate maximum
bandwidth required to transmit a CW signal?
A.
B.
C.
D.
2.4 kHz
150 Hz
1000 Hz
15 kHz
The Basic Radio Station
Basic Station Organization
• Station Equipment
• Receiver
• Transmitter
• Feed line
• Antenna
• Power Supply
• Accessory Station Equipment
• Repeaters
Special Stations You Will Use
(Repeaters)
• Repeaters are automated stations located at
high places that receive and then retransmit
your signal simultaneously.
• Dramatically improves range.
• The basic components of a repeater are the
same as your station: receiver, transmitter,
antenna and power supply.
Repeaters
• Repeaters are transmitting and receiving
at the same time often using the same
antenna.
• This requires a very high quality and
specialized filter to prevent the
transmitted signal from overpowering the
receiver.
• This filter is called a duplexer.
Repeater
Basic Station Accessories
• Human interface
accessories:
•
•
•
•
•
•
•
Microphones
Speakers
Earphones
Computer
Morse code key
TV camera
etc.
• Station
performance
accessories:
•
•
•
•
•
•
Antenna tuner
SWR meter
Amplifier
Antenna rotator
Filters
etc.
Accessory Equipment
T1F09 -- What type of amateur station
simultaneously retransmits the signal of another
amateur station on a different channel or
channels?
A.
B.
C.
D.
Beacon station
Earth station
Repeater station
Message forwarding station
T7A02 -- What is a transceiver?
A. A type of antenna switch
B. A unit combining the functions of a
transmitter and a receiver
C. A component in a repeater which filters out
unwanted interference
D. A type of antenna matching network
Questions?
Next Session
Chapter 3
Electricity, Components and Circuits