1. sources and the work of the original image makers is acknowledged)
What Are Radio Waves
And How Do We Use Them
(Pictures and Images in these slides were collected from a variety of internet
sources and the work of the original image makers is acknowledged)

2. Comments About Presentations
When I give the answer to a test question it is in red – BUT!
The best way to study for your test is to read the question pool and highlight and read only the right answer
The purpose of these slide presentations is to give you the big picture – help you know what terms mean – and help you to understand why certain answers are correct
Don’t be trying to memorize test question answers from the presentation!

3. Energy Moves Through Space as Electromagnetic Waves
Like Ripples on a Pond
only these are Electromagnetic Waves
What kind of wave carries radio signals
Between transmitting and receiving
Stations?
Electromagnetic
(T3A-07)
They move at the speed of light
(T3B-04)
(300,000,000 meters per second) (T3B-11)
Ie 7.5 laps around the earth in a second

4. Why Do We Call These Waves Electromagnetic?
Because they have 2 parts
Radio waves have an electric
Field
And a Magnetic Field
(T3B-03)
You have an electric field moving up and down and a magnetic field moving side to
side so they are a lot cooler than waves in a pond.

5. So Why Does it have to be the Electric Field that Moves Up and Down?
It doesn’t have to be that way
Electromagnetic waves are
Polarized – they are different
when laying down than when
standing up.
The electric field determines
which way they are polarized.
(T3B-02)
If the electrical field is going
up and down we are
Vertically Polarized
If the electrical field is side to
side then we are Horizontally
Polarized.
You are probably familiar with
Polarized sun glasses that
admit light only from specific
directions.

6. More About Wave Characteristics
The distance a wave travels
during one cycle is called
the Wavelength
(T3B-01)
One Cycle
The height of a wave is called
Its Amplitude
Big waves have more energy
than little waves.

7. Wavelength determines how many cycles the wave can go through in a second
If it has a short wavelength it goes up and down
a lot and is said to have a high frequency.
If it has a long wavelength it goes up and down
less often and is said to have a lower frequency
As the wavelength gets shorter the frequency increases.
(T3B-05)
If I have a piece of string and I cut it into short pieces
I will have more pieces than if I cut it into long
pieces.

8. Wavelength is how we tell what kind of Electromagnetic Energy it is.
Radio waves are
At least ½ cm (1/6th of
An inch) long.
Your radio communication
signal
They carry radio and
TV signals
Our cell phone signal
Radar
And we microwave
Our food with them
Shorter wavelengths are the light we see
Or the X rays that doctors use to look inside us.

9. Looking at Radio Spectrum
Radio waves for AM broadcast are over 100m long (around 2 foot ball field long)
Radio waves for FM broadcast are over 3 m long (around 10 feet)
Radio waves for your cell phone or TV are around a foot long

10. Another Way of Describing a Part of the Spectrum is Frequency
You can determine what kind of radio waves you are using either by its
Wavelength or its frequency (number of times it goes up and down or cycles in
one second). Frequency is a big number – a 10 meter wavelength cycles
30,000,000 times a second – we say Megahertz.

11. Radio Waves that Will be Important to you when you get your license
Very High Frequency (VHF) – from about 10 meters to 1 meter
We also describe it by how many cycles it can make in one second
VHF is 30 Megahertz to 300 Megahertz (T3B-08).

12. Another Important Frequency
Ultra High Frequency (UHF) goes from 300 megahertz to 3 gigahertz
(T3B-09)
(giga means billion)

13. For Amateur Radio Operators Wanting to Talk Around the World
High Frequency (HF) goes from 3 megahertz to 30 megahertz
(T3B-10)

14. We Can Describe Which Part of the Radio Spectrum we are talking about by either frequency or wavelength
Since wavelength and frequency are
related you must be able to
convert back and forth.
(T3B-06)

15. Lets Demonstrate 300/ 30 MHz = 10 meters 300/frequency = wavelength
(T3B-06)
By George I do believe it works

16. By Using Only Certain Wavelengths or Frequencies we can keep our signals separate so we don’t all pile up on top of everyone else
In the US the Federal Communications Commission (FCC) divides up who gets to
use what frequencies. Almost everything requires some type of license.

17. So What Will A Ham Radio License Let You Use
Notice that the
Property we are
Using to identify
Different “bands”
We are allowed
To use is
Wavelength.
(T3B-07)
Very important
For our local
Communication
2 Meters
And
70 centimeter
(centi – means 1/100th so
70 centimeters is 0.7 meters)

18. Technician Bands 6 meters is 50 to 54 MHz 2 meters is 144 to 148 MHz
(but you will need a separate radio for this band)
2 meters is 144 to 148 MHz
(most of our radios are designed for this frequency)
1.25 meters is 222 to 225 MHz
(you will need a special radio for this or a specific type of Baofeng radio)
70 cm is 420 to 450 MHz
(if you buy a Baofeng radio it also does this frequency)

19. A Side Note on 70 cm (One of the Baofeng Radio bands)
Amateur operators have what is called
a secondary allocation there. This
means that if the primary user (US Military)
is using the frequency you must stop
your talking and let them use it.
(This only really effects people near a few
East Coast military bases)

20. Questions they may ask You could memorize the answers (T1B-03)

21. Or You Can Make Use of Your 300 formula you already learned
(T1B-03)
300/ 6 = 50 MHz you know immediately it’s A or B
(with a little memory you know 6 meters is the lower end of the band so it has
To be B)

22. Try Again
(T1B-04)
300 / = just less than 2 pick A (yes you can bring a calculator to the
test)
(T1B-05)
300 / 0.7 = only C is even close

23. Finishing Off the Last of These Questions
300 / 0.23 = only B is even close
300 / = only D is even close

24. Interesting but Why Do Amateur Radio Operators have frequencies spread all over the map?
There are 24 different
Bands on that chart!
Why would Amateur
Operators want their
authorized frequencies
scattered?

25. Different Frequencies Behave Differently – more options means more chances to get the message through
VHF and UHF frequencies that
Technicians use operate Line
Of sight.
That means the radio antennas have to have an open straight line between
them.
Nice things radio waves are better than eye balls – I can’t see 50 miles but a
2 meter radio wave can travel that far.

26. So That Means 2 meter Radios are Good for 50 miles?
Well – maybe not
The earth is curved. Depending on
how high the antenna’s are sooner
or later the earth will get in the way.
The distance two stations can
Communicate directly by line of sight is
the radio horizon. (T3C-10)
Great Dedication – but is it practical?
For people on the ground holding a radio
at face height you have about 6 miles
before the earth will block you.

27. Ok But I Can Still Do a Lot With 6 miles
Except that the earth isn’t
Perfectly curved either.
Stuff can get in the way.
Sometimes if you are driving
Along listening or talking
On the radio the signal will
Become strong and then
Suddenly weak.
This is called Picket Fencing
(T3A-06)
If your radio signal was good
And then suddenly its weak
Try moving a few feet one
Way or the other.
(T3A-01)

28. If I Have Stuff in the Way Will it Always Block My Signal?
Why are UHF signals often
More effective than VHF
Signals inside buildings?
The shorter wavelength allows
Them to more easily penetrate
The structure of buildings.
(T3A-02)
Nothing is going to drill through a mountain
But!
Higher frequency bands will drill through
Buildings – particularly if you want to talk
To someone inside.
Drill through 6 meters - poor
2 meters – marginal
70 cm - not bad
33 cm – pretty good
(so we are starting to see why having multiple frequency bands is useful)

29. Are There Ways Around Obstructions besides moving or drilling through?
An obstruction can bend radio waves
And send waves into places we shouldn’t
Be able to hit.
Knife Edge diffraction can cause a
Signal to be heard even when there is
An obstruction in the way. (T3C-05)
Knife edge diffraction works
Better for long wave lengths
70 cm doubtful
1.25 meters good
2 meters better
6 meters best
The Pam Flemming Case.

30. Ok If Nothings In the Way I Can Get 6 miles – right?
That depends on whether
something eats up the
power in your signal.
Atmospheric moisture eats radio
energy for lunch!
Short radio antennas are compact
and nice, but they have a lot of
electronics to fool the radio wave into
thinking the antenna is longer. These
electronics eat-up your transmission power
Its called loading an antenna – you insert
An inductor – (wire coil) into the antenna
To make it electrically longer (T9A-14)

31. Beating the Eating I Love Eating 33 cm And 70 cm Wavelengths!
(These wavelengths have big
problems with atmospheric
moisture)
1.25 meter and
2 meter wavelengths
are good for light
eating.
6 meters for lunch?
Please tell me your kidding
Atmospheric Humidity

32. So What About the Lousy Antennas
Whats inside a rubber
Duck antenna
(Coil structures eat
Power)
Rubber Ducky Not the One
he won’t help you have some
fun.
A rubber duck antenna does not receive or transmit as
effectively as a full size antenna. (T9A-04)
To really mess-up use a handheld radio in a car – the metal
shell of your car intercepts signals.
The signal from inside your car is much weaker than outside
(T9A-07)
(like about 1/10th as strong – Tithing is a true principle but not when it comes
To radio signals)

33. A Baofeng (and most handheld radios from other manufactures) comes with a rubber duck antenna
This is a rubber duck antenna.
By the time it wastes a good
part of your radios power you
will only get about 2.5 to 3 miles
(talking to another person on the ground).
You can buy a different antenna
for less than $10

34. Ok So What is a Full Size Antenna?
Just like the length of a string determines
the sound it makes naturally (resonate)
so to the length of the antenna determines
what wavelength of radio wave it sends out
naturally.
Most VHF and UHF voice
Communication uses an
Antenna is a simple straight
Up and down wire.
A vertical antenna will produce a vertically Polarized radio wave with the Electrical field perpendicular to the earth
(T9A-02)
The antenna should be
1/4th the wavelength – good
½ the wavelength – better
So a quarter wave 2 meter antenna is
1/4th of the wavelength or about 19
Inches (T9A-08)
A half wave 6 meter antenna is
About 112 inches long. (T9A-09)
(That’s just shy of 10 feet long – wouldn’t that be
Fun to put on top of your car)

35. Full Size Antenna Size Leads to Some Practical Considerations
112 inches for
½ wave
6 meter antenna
(T9A-09)
49 inches for
A 5/8th wave
2 meter antenna
About 17
Inches for
a 70 cm
½ wave
antenna
Still nearly 5 ft for a ¼ wave
6 meter antenna
We can probably live with that
The 70 cm band is the only one where a full size handheld
Antenna is really practical. For 4 to 5 mile local communication
With a handheld radio 70 cm may actually work better than 2 meters.

36. Ok – If I have a good antenna and nothing in the way can I get 6 miles?
Maybe not.
What’s wrong with these
Pictures?

37. What Direction are most Antennas for VHF and UHF transmissions Oriented?
That’s right - Vertical
That means the radio waves will be
Vertically polarized with the electric field going
Up and down and the magnetic side to side

38. Which way is this antenna pointing
So the radio waves
will be Horizontally
Polarized with the
electrical field going
side to side and the
magnetic up and down
Yipes – Stripes its almost
Horizontal!
What can happen when antennas at
Opposite ends of a VHF or UHF radio
Link are not using the same polarization?
The signals will be significantly weaker
(T3A-04)
(could be as bad as 50 times weaker)

39. So If I Use a Full Size Antenna on my handheld radio I point the antenna up and there is nothing in the way I can get 6 miles- right?
17 inch ½ wave
On 70 cm
19 inch ¼ wave
On 2 meters
Well – maybe not. Handheld radios only have
3 to 5 watts of power (A light bulb is 75 watts) so
the signal may not be strong enough in the
right direction to beat the atmosphere eating
up your small amplitude radio waves.
(Our tests show about 4 to 5 mile maximum with Handheld
And a full size antenna)

40. The Antenna Also Determines the Shape and Direction the radio waves go in
If your not aiming at the
Target – you might not
Hit it.

41. Concepts of Gain and Take-Off Angle
We start out thinking about a “Isotropic Radiator”
that puts out electromagnetic waves equally in
all directions.
The sun is one of our best examples.

42. Isotropic Radiators Make Poor Antennas
And I don’t think this is
Part of my emergency
Communication plan.
I’m on the ground

43. Antenna Gain
Gain is the increase in signal strength in a specified direction
Compared to a reference antenna. (T9A-11)
If I can aim more of my radio wave energy out across the ground I can
Get my signals further before the atmosphere eats them.
1/4th
Wave
Antenna
Radiation
Pattern
Direction of strongest signal is the
Take-off angle
(Keeping it low toward the ground is a good thing)
Note that the ground is actually part of the antenna in shaping radio wave aim

44. So What Can I Do With Take-Off Angle?
The take-off angle of a
Half wave antenna is closer
To the ground than a
Quarter wave
¼ wave antenna - good (but it’s take-off angle is around 27 degrees)
½ wave antenna – better (lower take-off angle)
5/8th wave antenna – best (lowest take-off angle – around 16 degrees)
So why use a properly mounted 5/8th wave antenna for VHF and UHF?
Because it offers a lower angle of radiation and more gain than a 1/4th wave (T9A-12)
This is why you may actually get better range on a handheld radio using
a 17 inch 1/2 wave antenna on the 70 cm band than using a 19 inch ¼ wave
antenna on 2 meters.

45. I Have Another Idea Take-off angle Even though I’m getting more of my
Energy down on the ground I’m
Still putting the energy out in a 360
Degree circle
What if the person I want to talk to is
only in one direction?

46. What If I Could Aim My Radio waves in just one direction across the ground?
It turns out you can using
A beam antenna
A beam antenna is an
antenna that concentrates
signals in one direction.
(T9A-01)

47. So What Does This Magic Antenna Look Like?
The Yagi Antenna
(Some of you old enough
to remember old TV
Antennas outside your
home think this looks
familiar. That’s because
old TV antennas were
Yagis)
The Quad
Antenna
The dish antenna
(Some of you are thinking about the satellite dish on your house)
So what type of antenna are a quad, yagi, and
Dish?
Directional Antennas
(T9A-06)

48. There is one not so little problem with directional antennas
They are not so little!
Its hard for them to be practical for most mobile
Communication
Except maybe Fox-Hunting

49. But I Want My Full 6 miles And your still giving me only 4 or 5 with my handheld radio
Fact of life 1 – a little under 20 inches is about the
Maximum practical antenna length for a handheld
Fact of life 2 – 70 cm is the only radio band where
You can get a ½ wave or 5/8th wave antenna that
Gets good gain and aims the signal near the
Ground and still be less than 20 inches.
Fact of life 3 – the atmosphere loves to eat 70 cm
wavelengths and a handheld starts out with only
4 or 5 watts of power.

50. Try This 49 inch 5/8th wave 2 meter Magmount antenna
Put a magmount antenna on the
Car
Run the connecting cable through
The window or around the edge of
The door
Hook your handheld radio up to the
External antenna with the magmount
Connecting cable.
You think this is the roof of your car but the
Antenna thinks it’s the nicest ground plane
In town.
Why are VHF and UHF mobile
Antennas mounted in the center
Of the roof?
A roof mount antenna provides the most
Uniform radiation pattern.
(T9A-13)
This set up will get you 7 or 8
Miles of range

51. Wait A Minute – Back Up I thought you said for antennas at head level the earth would get in the way after 6 miles
Radio waves will bend just a little so the radio horizon is further away than the
Optical horizon for light – that’s how I got my extra mile or two.
Why do UHF and VHF radio waves travel further than the visual line of sight?
The earth seams less curves to radio waves than light. (T3C-11)
The longer the wave length – the better the bending
70 cm - I don’t think so
2 meters – good
6 meters – Better (except a 10 foot antenna on your car is impractical)
10 meters – Best (except a nearly 20 foot antenna on a car is not going to happen)

52. But a 6 or even 8 mile range will not cover Carbondale Ward
We are not even letting
Carbondale and
Murphysboro Talk!
Range with car top
5/8th wave 2 meter
Range with ½ wave
On 70 cm
Range of Handheld
With Rubber Duck
I don’t think it is
practical to
extend ranges
this way.

53. So how do I beat a 6 mile limit?
Great Spot to Put an Antenna where
no one will see
What's in Your
Attic?
The home base station –
Not very portable but it gets the antenna
in the air.

54. Height and the Radio Horizon
Base Station to
Base Station Range
Of course to get this
range the radios still
have to have enough
power to beat
atmospheric signal
eating and have no
obstructions.
Base Station to
Mobile Radio
Obviously a network of Base Stations
Can talk across Carbondale Ward

55. Jacking Up the Power A Bit
This power is enough to push a signal out
About 20 to 30 miles (if there no obstructions
And your antenna is on a high enough spot)
Power Amplifier
Handheld

56. Of Course You Can Use a Real Mobile Radio
You have to
Direct connect power
To the battery
(That means going
Through the firewall under
The dash and across the
Engine compartment)
Has as much
Power as a Home
Base Station.

57. Then There is How Do We Talk Across the Stake
Base to Base Range

58. Idea – How About Relaying Messages What would be really cool is if we could do it automatically
So far we have talked about direct
Radio to Radio communication with
both radios set to the same frequency.
This is called
Simplex communication
(T2B-01)
Next we will consider a repeater
that takes a radio signal and
automatically repeats it back.

59. Repeaters Get Around Objects and Extend Range
Repeaters can
resend your message
with MORE POWER
than your little
handheld has.
There are options for putting repeater antennas at higher places
Than most of us have access to.
(This is the Carbondale Illinois Repeater Location)
A handheld radio can normally reach
Repeaters 15 to 20 miles away.

60. Of Course Even a Repeater be Obstructed. Now What?
Objects that
Block radio waves
Also reflect them.
Shift around and look for a reflected path.

61. Remember Too That Object Edges bend and Refract Waves
Obstruction

62. But How Can It Listen and Resend the Message on the Same Frequency without tripping over itself?
Well actually – It Can’t
Repeaters use one frequency to receive
Signals and another to send them
We call this Duplex Communication.
Example – the Alto Pass Repeater sends
Out signals at MHz
But it receives signals on MHz
The most common offset on 2 meter repeaters is plus or minus 600 KHz
(T2A-01)

63. More on Repeater Offsets
The Carbondale 70 cm repeater sends out
Signals at MHz
But it receives signals on MHz
The most common repeater offset on 70 cm
Is 5 MHz
(T2A-03)
Notice that the Carbondale 70 cm repeater receives at a higher frequency than
It sends – called a positive offset.
The Alto pass receives at a lower frequency than
What it sends on – called a negative offset.
Send on MHz
Receives on MHz

64. A Repeater Test Question

65. To Use a Repeater You Must Set Your Radio to Listen on the Repeater Output and Send on the Repeater Input
Fortunately most radios have a duplex setting that
automatically knows which way and how much to
offset.
Set the repeaters send frequency and the radio takes
care of what you need to do to send to the repeater.
(On cheap Chinese Baofeng (Pofeng) radios there is U.S. programming software
that will take care of the problem automatically)
Great – I get the feeling its telling me a repeater might not work for me even
If I have got my radio set to duplex with the proper offsets.
(Now what’s all that letter gibberish that sounds like a government agency)

66. So What is a CTCSS Tone for Access?
We’ve all heard of dog whistles that dogs can hear but people
can’t.
CTCSS stands for Continuous Tone Coded Squelch System.
You can set you radio to put out a hum that people can’t hear
but a repeater can. It tells the repeater when you want your
message repeated. If you don’t send the tone it means don’t
repeat this message.
Radio operators call them PL tones
(Do you want to say Continuous Tone Coded Squelch
System when PL tone will do?)
DCS is digital code
Squelch – it’s a sub audible
Telegram message sent
Over and over again.
(seldom used on amateur
Repeaters)
A tone burst is a sequence of tones that have
to be sent to a repeater to have your message
repeated. (Common in Europe)

67. So What Could the Test Ask?
Note this question is not describing a digital sequence being sent or a burst of tones.
It is asking about a constant tone - the PL tone or CTCSS pick D

68. So if Repeaters are so cool when would we consider communicating simplex instead of a using a repeater?
The official FCC answer
When the stations can communicate directly without using a repeater
(T2B-12)
A few thoughts for emergency response
1- only a few of our area repeaters have back-up power so the repeater will stop
working if there is a power failure. (If regular telephones are out there is a
very good chance the power is out too).
2- only one semi-nearby repeater in Puducah Kentucky has enough back-up
power to last more than a few days.
3- repeaters are listening frequencies for a lot of people (including bad guys).
You may not want to tell the world that so and so is alone with her kids
because her husband is dead or injured.
(Find a frequency were people are less likely to listen – speaking in code on
amateur radio is illegal – it turns out most scanners can’t listen to meters)

69. At the End of the Day there are limits to what we can do with line of sight signals
Time to start thinking about
whether some of those
other bands have an
alternative to line of sight
propagation

70. HF has a different Propagation Mode
Its called a sky wave – the radio wave
goes up into the air – hits an ionized
layer in the upper atmosphere called
the ionosphere and Is reflected back
down to earth.
The stations communicating are far
From the line of sight of each other.
The amount of ionization varies from day to night, season to season, and
Year to year due to the sunspot cycle.
What part of the atmosphere enables propagation of radio signals around the
World?
The ionosphere.
(T3A-11)

71. Whether a Radio Wave Reflects Back Depends on its Frequency and the angle it hits at
Lower frequencies will reflect back to earth at more angles than higher frequencies
At some point the frequency is so high that it will just pass right out into space.
This upper limit is called the Maximum usable frequency (MUF).

72. Of Course Things Can Bounce In Many Frustrating Ways

73. Another Effect of Bouncing Around
Vertically Polarized
The signal polarization gets
Scrambled.
Horizontally
Polarized
(elliptical refers to be polarized in all different directions)
Result
(T3A-09)

74. What Kind of Antenna is Used for HF?
They are called dipoles and they are
About ½ a wave length long.

75. Why Do We Pull Them Out Horizontal
Because they are have a wavelength long
80 meters – ½ is 40 meters or about 130 feet!
That would be a lot of fun to support in the air!

76. Dipole Radiation Pattern
Direction of Wire

77. If a Dipole Antenna is laid out Horizontally – Which Way are the Radio Waves Polarized?
Oh Yes – Horizontal!

78. Brain Teaser Lets Think
Higher frequency means the wave length is shorter
A typical dipole is ½ wavelength long
If the wave length got shorter – what happened to the antenna?

79. How Many of You Picked This?

80. The Bad News for People with Technician Licenses
The only HF band you can use to
Talk on is a little bit of the 10 meter
Band.
Ten meters is almost always above the Maximum Usable Frequency and will
Almost always go out into space.
(That’s one of the reasons its nice if some people take extra tests and get
A general or extra license that allow them to use a lot of HF frequencies)
Why are direct (not via repeater) UHF signals seldom heard stations outside your
local coverage area?
UHF signals are usually not reflected by the ionosphere (T3C-01)

81. So Are All Technicians just SOL?
Not quite – the sun has an 11 year sun spot cycle.
When the sun is really stormy it does a much
Better job of ionizing the atmosphere.
When we juice up the F layer in the atmosphere we can bounce
Skywaves back to earth on 10 and 6 meters.

82. There is Another Catch In order for sunlight to ionize the atmosphere
it has to be shining on it.
That happens only during the day.
At night the atmosphere starts deionizing
and the maximum usable frequency goes
down – and there goes our 10 and 6 meter
Skywave Skip.
Which bands provide long distance communication during the peak of the
Sunspot cycle?
6 and 10 meters. (T3C-12)
What is generally the best time for long distance 10 meter propogation via the F
Layer?
From dawn to shortly after sunset during periods of peak sunspot activity (T3C-09)

83. There is Also Another Way to Catch a Break
There is a lower layer of the atmosphere
That can be ionized for short periods of
Time and will reflect 6 or even 2 meter
Frequencies back to earth.
It is called the E layer and its sporadic
Ionization is called sporadic E.
It particularly effects 6 meters. Sudden
Band opening give 6 meters the nick-name
“the magic band”
What might be happening when VHF signals are being received from long distances?
Signals are being reflected from a sporadic E layer
(T3C-02)
Side note – 6 meters requires a separate radio to use – right now there are few Church members and
no plans to use 6 meters.

84. Related Question
Which type of the following propagation types is most commonly associated with
Strong over the horizon signals on the 10, 6, and 2 meter bands?
Sporadic E
(T3C-04)
Do note that sporadic E is not a world
Wide reflecting layer in the atmosphere
So the places that “open up” are selective
Not only in when it happens but where.
The magic band (6 meters) often likes
South America – good for our bilingual
members but not a particularly good
route for reporting emergency information
around the ward or stake.

85. Getting Atmospheric Reflection with Lucky Shots
Meteor Scatter
Meteors leave an ionization trail behind them
that can be used to reflect radio signals –
especial 6 meters (the Magic Band)
Which band is best suited for communicating
via meteor scatter?
6 meters
(T3C-07)

86. Another Lucky Shot Auroral Scatter
The northern lights are atmospheric ionization.
Not surprisingly we can bounce radio signals
off them.
Unfortunately, signals bounce all over in the
pretty, but messy ionization area. The result
is signals very in strength and are often
distorted.
What is a characteristic of VHF signals received
by auroral reflextion?
The signals experience rapid fluctuations of
strength and are often distorted.
(T3C-03)

87. Getting Your Ducts in a Row
Normally air
Temperature gets
Lower the higher
You go in the
Atmosphere.
In a temperature inversion you get cold air on the ground and a warm
layer above. Air pollution people hate them – but they create opportunity for
long distance radio communication in VHF and UHF bands.

88. What Does a Temperature Inversion Do for Radio
Plan A – the change in air density of
the warm air above bounces the
signal back down to the ground, where
it may bounce back up again.
Like a ball bouncing on the ground –
bounces weaken signals with each
bounce.
Plan B – the signal gets in the warm layer and
Bounces between cold layers – lot less energy
Loss.
Catch – it skips everything in between and
Comes at an unknown spot on the other end.
What causes tropospheric ducting?
Temperature inversions in the atmosphere
(T3C-08)

89. Problems for Emergency Communication
Simplex radio to radio will
Always work if the two radios
Are still in tact.
Repeaters may or may not
Be running.
Sporadic E, meteor scatter,
And tropospheric ducting are
Not reliably available.

90. Here is Something that works almost all the time for 2 meters on up
What mode is responsible for allowing over-the-horizon VHF and UHF
Communications to ranges of about 300 miles on a regular basis?
Tropospheric Scatter
(T3C-06)
You’ve seen these particles
at work when you watch
stars twinkle at night.
Bounce the radio signal off of
Particles in the lower atmosphere