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)

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!

Energy Moves Through Space as Electromagnetic Waves

Like Ripples on a Pondonly these are Electromagnetic Waves

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

What kind of wave carries radio signalsBetween transmitting and receivingStations?

Electromagnetic(T3A-07)

Why Do We Call These Waves Electromagnetic?

Because they have 2 parts

Radio waves have an electricField

And a Magnetic Field(T3B-03)

You have an electric field moving up and down and a magnetic field moving side toside so they are a lot cooler than waves in a pond.

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 arePolarized – they are differentwhen laying down than whenstanding up.

The electric field determineswhich way they are polarized.(T3B-02)

If the electrical field is goingup and down we areVertically Polarized

If the electrical field is side toside then we are HorizontallyPolarized.

You are probably familiar withPolarized sun glasses thatadmit light only from specificdirections.

More About Wave Characteristics

One Cycle

The distance a wave travelsduring one cycle is calledthe Wavelength(T3B-01)

The height of a wave is calledIts Amplitude

Big waves have more energythan little waves.

Wavelength determines how many cycles the wave can go through in a second

If it has a short wavelength it goes up and downa lot and is said to have a high frequency.

If it has a long wavelength it goes up and downless 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 piecesI will have more pieces than if I cut it into longpieces.

Wavelength is how we tell what kind of Electromagnetic Energy it is.

Radio waves areAt least ½ cm (1/6th of

An inch) long.

Your radio communicationsignal

They carry radio andTV signals

Our cell phone signal

Radar

And we microwaveOur food with them

Shorter wavelengths are the light we see

Or the X rays that doctors use to look inside us.

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

Another Way of Describing a Part of the Spectrum is Frequency

You can determine what kind of radio waves you are using either by itsWavelength or its frequency (number of times it goes up and down or cycles inone second). Frequency is a big number – a 10 meter wavelength cycles30,000,000 times a second – we say Megahertz.

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 secondVHF is 30 Megahertz to 300 Megahertz (T3B-08).

Another Important Frequency

Ultra High Frequency (UHF) goes from 300 megahertz to 3 gigahertz(T3B-09)

(giga means billion)

For Amateur Radio Operators Wanting to Talk Around the World

High Frequency (HF) goes from 3 megahertz to 30 megahertz(T3B-10)

We Can Describe Which Part of the Radio Spectrum we are talking about by either

frequency or wavelength

Since wavelength and frequency arerelated you must be able toconvert back and forth.

)()(

300inmeterswavelength

zinmegahertFrequency

(T3B-06)

Lets Demonstrate

300/ 30 MHz = 10 meters

By George I do believe it works

300/frequency = wavelength(T3B-06)

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 touse what frequencies. Almost everything requires some type of license.

So What Will A Ham Radio License Let You Use

Notice that theProperty we areUsing to identifyDifferent “bands”We are allowedTo use isWavelength.(T3B-07)

Very importantFor our localCommunication

2 Meters

And

70 centimeter(centi – means 1/100th so70 centimeters is 0.7 meters)

Technician Bands6 meters is 50 to 54 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)

70 cm is 420 to 450 MHz(if you buy a Baofeng radio it also does 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)

A Side Note on 70 cm(One of the Baofeng Radio bands)

Amateur operators have what is calleda secondary allocation there. Thismeans that if the primary user (US Military)is using the frequency you must stopyour talking and let them use it.(This only really effects people near a fewEast Coast military bases)

Questions they may ask

You could memorize the answers

(T1B-03)

(T1B-04)

Or You Can Make Use of Your 300 formula you already learned

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 hasTo be B)

(T1B-03)

Try Again

300 / 146.52 = just less than 2 pick A (yes you can bring a calculator to the test)

300 / 0.7 = 429 - only C is even close(T1B-05)

(T1B-04)

Finishing Off the Last of These Questions

300 / 0.23 = 1304 only B is even close

300 / 223.5 = 1.34 only D is even close

Interesting but Why Do Amateur Radio Operators have frequencies

spread all over the map?

There are 24 differentBands on that chart!

Why would AmateurOperators want theirauthorized frequenciesscattered?

Different Frequencies Behave Differently – more options means more chances to get

the message through

VHF and UHF frequencies thatTechnicians use operate LineOf sight.

That means the radio antennas have to have an open straight line betweenthem.

Nice things radio waves are better than eye balls – I can’t see 50 miles but a2 meter radio wave can travel that far.

So That Means 2 meter Radios are Good for 50 miles?

Well – maybe notThe earth is curved. Depending onhow high the antenna’s are sooneror later the earth will get in the way.

Great Dedication – but is it practical?

For people on the ground holding a radioat face height you have about 6 milesbefore the earth will block you.

The distance two stations canCommunicate directly by line of sight isthe radio horizon. (T3C-10)

Ok But I Can Still Do a Lot With 6 miles

Except that the earth isn’tPerfectly curved either.

Stuff can get in the way.

Sometimes if you are drivingAlong listening or talkingOn the radio the signal willBecome strong and thenSuddenly weak.This is called Picket Fencing(T3A-06)

If your radio signal was goodAnd then suddenly its weak

Try moving a few feet oneWay or the other.(T3A-01)

If I Have Stuff in the Way Will it Always Block My Signal?

Nothing is going to drill through a mountainBut! Higher frequency bands will drill through

Buildings – particularly if you want to talkTo someone inside.

Drill through 6 meters - poor2 meters – marginal70 cm - not bad33 cm – pretty good

(so we are starting to see why having multiple frequency bands is useful)

Why are UHF signals oftenMore effective than VHFSignals inside buildings?

The shorter wavelength allowsThem to more easily penetrateThe structure of buildings.(T3A-02)

Are There Ways Around Obstructions besides moving or

drilling through?

An obstruction can bend radio wavesAnd send waves into places we shouldn’tBe able to hit.

Knife Edge diffraction can cause aSignal to be heard even when there isAn obstruction in the way. (T3C-05)

The Pam Flemming Case.

Knife edge diffraction worksBetter for long wave lengths

70 cm doubtful1.25 meters good2 meters better6 meters best

Ok If Nothings In the Way I Can Get 6 miles – right?

That depends on whethersomething eats up thepower in your signal.

Short radio antennas are compactand nice, but they have a lot ofelectronics to fool the radio wave intothinking the antenna is longer. Theseelectronics eat-up your transmission power

Atmospheric moisture eats radioenergy for lunch!

Its called loading an antenna – you insertAn inductor – (wire coil) into the antennaTo make it electrically longer (T9A-14)

Beating the Eating

Atmospheric Humidity

I Love Eating 33 cmAnd 70 cmWavelengths!(These wavelengths have bigproblems with atmosphericmoisture)

1.25 meter and2 meter wavelengthsare good for lighteating.

6 meters for lunch?Please tell me your kidding

So What About the Lousy Antennas

Rubber Ducky Not the Onehe won’t help you have somefun.

Whats inside a rubberDuck antenna(Coil structures eatPower)

A rubber duck antenna does not receive or transmit aseffectively as a full size antenna. (T9A-04)

To really mess-up use a handheld radio in a car – the metalshell 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 comesTo radio signals)

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 goodpart of your radios power youwill only get about 2.5 to 3 miles(talking to another person on the ground).

You can buy a different antennafor less than $10

Ok So What is a Full Size Antenna?

Just like the length of a string determinesthe sound it makes naturally (resonate)so to the length of the antenna determineswhat wavelength of radio wave it sends outnaturally.

Most VHF and UHF voiceCommunication uses anAntenna is a simple straightUp 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 be1/4th the wavelength – good½ the wavelength – better

A half wave 6 meter antenna isAbout 112 inches long. (T9A-09)

(That’s just shy of 10 feet long – wouldn’t that beFun to put on top of your car)

So a quarter wave 2 meter antenna is1/4th of the wavelength or about 19Inches (T9A-08)

Full Size Antenna Size Leads to Some Practical Considerations

About 17Inches fora 70 cm½ waveantenna

We can probably live with that

49 inches forA 5/8th wave 2 meter antenna

112 inches for½ wave6 meter antenna(T9A-09)

Still nearly 5 ft for a ¼ wave6 meter antenna

The 70 cm band is the only one where a full size handheldAntenna is really practical. For 4 to 5 mile local communicationWith a handheld radio 70 cm may actually work better than 2 meters.

Ok – If I have a good antenna and nothing in the way can I get 6 miles?

Maybe not.

What’s wrong with thesePictures?

What Direction are most Antennas for VHF and UHF transmissions Oriented?

That’s right - Vertical

That means the radio waves will beVertically polarized with the electric field goingUp and down and the magnetic side to side

Which way is this antenna pointing

Yipes – Stripes its almostHorizontal!

So the radio waveswill be HorizontallyPolarized with theelectrical field goingside to side and themagnetic up and down

What can happen when antennas atOpposite ends of a VHF or UHF radioLink are not using the same polarization?

The signals will be significantly weaker(T3A-04)

(could be as bad as 50 times weaker)

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 waveOn 70 cm

19 inch ¼ waveOn 2 meters

Well – maybe not. Handheld radios only have3 to 5 watts of power (A light bulb is 75 watts) sothe signal may not be strong enough in theright direction to beat the atmosphere eatingup your small amplitude radio waves.

(Our tests show about 4 to 5 mile maximum with HandheldAnd a full size antenna)

The Antenna Also Determines the Shape and Direction the radio

waves go in

If your not aiming at theTarget – you might notHit it.

Concepts of Gain and Take-Off Angle

We start out thinking about a “Isotropic Radiator”that puts out electromagnetic waves equally inall directions.

The sun is one of our best examples.

Isotropic Radiators Make Poor Antennas

I’m on the ground

And I don’t think this isPart of my emergencyCommunication plan.

Antenna Gain

If I can aim more of my radio wave energy out across the ground I canGet my signals further before the atmosphere eats them.

1/4th

WaveAntennaRadiationPattern

Direction of strongest signal is theTake-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

Gain is the increase in signal strength in a specified directionCompared to a reference antenna. (T9A-11)

So What Can I Do With Take-Off Angle?

The take-off angle of aHalf wave antenna is closerTo the ground than aQuarter 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 usinga 17 inch 1/2 wave antenna on the 70 cm band than using a 19 inch ¼ waveantenna on 2 meters.

I Have Another Idea

Take-off angle

Even though I’m getting more of myEnergy down on the ground I’mStill putting the energy out in a 360Degree circle

What if the person I want to talk to isonly in one direction?

What If I Could Aim My Radio waves in just one direction across the ground?

It turns out you can usingA beam antenna

A beam antenna is anantenna that concentratessignals in one direction.(T9A-01)

So What Does This Magic Antenna Look Like?

The Yagi Antenna

(Some of you old enoughto remember old TVAntennas outside yourhome think this looksfamiliar. That’s becauseold TV antennas wereYagis)

The dish antenna(Some of you are thinking about the satellite dish on your house)

The QuadAntenna

So what type of antenna are a quad, yagi, andDish?Directional Antennas(T9A-06)

There is one not so little problem with directional antennas

They are not so little!

Its hard for them to be practical for most mobileCommunication

Except maybe Fox-Hunting

But I Want My Full 6 milesAnd your still giving me only 4 or 5 with my handheld radio

Fact of life 1 – a little under 20 inches is about theMaximum practical antenna length for a handheld

Fact of life 2 – 70 cm is the only radio band whereYou can get a ½ wave or 5/8th wave antenna thatGets good gain and aims the signal near theGround and still be less than 20 inches.

Fact of life 3 – the atmosphere loves to eat 70 cmwavelengths and a handheld starts out with only4 or 5 watts of power.

Try This

49 inch 5/8th wave 2 meterMagmount antenna

You think this is the roof of your car but theAntenna thinks it’s the nicest ground planeIn town.

Put a magmount antenna on theCar

Run the connecting cable throughThe window or around the edge ofThe door

Hook your handheld radio up to theExternal antenna with the magmountConnecting cable.

This set up will get you 7 or 8Miles of range

Why are VHF and UHF mobileAntennas mounted in the centerOf the roof?A roof mount antenna provides the mostUniform radiation pattern.(T9A-13)

Wait A Minute – Back UpI 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 theOptical 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 so2 meters – good6 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)

But a 6 or even 8 mile range will not cover Carbondale Ward

Range of HandheldWith Rubber Duck

Range with ½ waveOn 70 cm

Range with car top5/8th wave 2 meter

We are not even lettingCarbondale andMurphysboro Talk!

I don’t think it ispractical toextend rangesthis way.

So how do I beat a 6 mile limit?Great Spot to Put an Antenna whereno one will see

What's in Your Attic?

The home base station –

Not very portable but it gets the antennain the air.

Height and the Radio Horizon

Base Station toMobile Radio

Base Station toBase Station Range

Of course to get thisrange the radios stillhave to have enoughpower to beatatmospheric signaleating and have noobstructions.

Obviously a network of Base StationsCan talk across Carbondale Ward

Jacking Up the Power A Bit

Handheld

Power Amplifier

This power is enough to push a signal outAbout 20 to 30 miles (if there no obstructionsAnd your antenna is on a high enough spot)

Of Course You Can Use a Real Mobile Radio

Has as muchPower as a HomeBase Station.

You have toDirect connect powerTo the battery(That means goingThrough the firewall underThe dash and across theEngine compartment)

Then There is How Do We Talk Across the Stake

Base to Base Range

Idea – How About Relaying Messages

What would be really cool is if we could do it automatically

So far we have talked about directRadio to Radio communication with both radios set to the same frequency.

This is calledSimplex communication(T2B-01)

Next we will consider a repeaterthat takes a radio signal andautomatically repeats it back.

Repeaters Get Around Objects and Extend Range

There are options for putting repeater antennas at higher placesThan most of us have access to.(This is the Carbondale Illinois Repeater Location)

Repeaters canresend your messagewith MORE POWERthan your littlehandheld has.

A handheld radio can normally reachRepeaters 15 to 20 miles away.

Of Course Even a Repeater be Obstructed.

Now What?

Objects thatBlock radio wavesAlso reflect them.Shift around and look for a reflected path.

Remember Too That Object Edges bend and Refract Waves

Obstruction

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 receiveSignals and another to send them

We call this Duplex Communication.

Example – the Alto Pass Repeater sendsOut signals at 146.86 MHz

But it receives signals on 146.26 MHz

The most common offset on 2 meter repeaters is plus or minus 600 KHz(T2A-01)

More on Repeater OffsetsThe Carbondale 70 cm repeater sends outSignals at 442.025 MHz

But it receives signals on 447.025 MHz

The most common repeater offset on 70 cmIs 5 MHz(T2A-03)

Notice that the Carbondale 70 cm repeater receives at a higher frequency thanIt sends – called a positive offset.

The Alto pass receives at a lower frequency thanWhat it sends on – called a negative offset.

Send on 146.85 MHzReceives on 146.25 MHz

A Repeater Test Question

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 thatautomatically knows which way and how much tooffset.

Set the repeaters send frequency and the radio takescare of what you need to do to send to the repeater.(On cheap Chinese Baofeng (Pofeng) radios there is U.S. programming softwarethat will take care of the problem automatically)

Great – I get the feeling its telling me a repeater might not work for me evenIf 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)

So What is a CTCSS Tone for Access?

We’ve all heard of dog whistles that dogs can hear but peoplecan’t.

CTCSS stands for Continuous Tone Coded Squelch System.You can set you radio to put out a hum that people can’t hearbut a repeater can. It tells the repeater when you want yourmessage repeated. If you don’t send the tone it means don’trepeat this message.

Radio operators call them PL tones(Do you want to say Continuous Tone Coded SquelchSystem when PL tone will do?)

DCS is digital codeSquelch – it’s a sub audibleTelegram message sentOver and over again.(seldom used on amateurRepeaters)

A tone burst is a sequence of tones that haveto be sent to a repeater to have your messagerepeated. (Common in Europe)

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

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 1.25 meters)

At the End of the Day there are limits to what we can do with line of sight signals

Time to start thinking aboutwhether some of thoseother bands have analternative to line of sightpropagation

HF has a different Propagation Mode

Its called a sky wave – the radio wavegoes up into the air – hits an ionizedlayer in the upper atmosphere calledthe ionosphere and Is reflected backdown to earth.

The stations communicating are farFrom the line of sight of each other.

The amount of ionization varies from day to night, season to season, andYear to year due to the sunspot cycle.

What part of the atmosphere enables propagation of radio signals around theWorld?

The ionosphere.(T3A-11)

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).

Of Course Things Can Bounce In Many Frustrating Ways

Another Effect of Bouncing Around

Vertically Polarized

Horizontally Polarized

The signal polarization getsScrambled.

Result(elliptical refers to be polarized in all different directions)

(T3A-09)

What Kind of Antenna is Used for HF?

They are called dipoles and they areAbout ½ a wave length long.

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!

Dipole Radiation Pattern

Direction of Wire

If a Dipole Antenna is laid out Horizontally – Which Way are the

Radio Waves Polarized?

Oh Yes – Horizontal!

Brain Teaser

Lets Think

Higher frequency means the wave length is shorter

A typical dipole is ½ wavelength longIf the wave length got shorter – what happened to the antenna?

How Many of You Picked This?

The Bad News for People with Technician Licenses

The only HF band you can use toTalk on is a little bit of the 10 meterBand.

Ten meters is almost always above the Maximum Usable Frequency and willAlmost always go out into space.

(That’s one of the reasons its nice if some people take extra tests and getA 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 yourlocal coverage area?

UHF signals are usually not reflected by the ionosphere (T3C-01)

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 muchBetter job of ionizing the atmosphere.

When we juice up the F layer in the atmosphere we can bounceSkywaves back to earth on 10 and 6 meters.

There is Another Catch

In order for sunlight to ionize the atmosphereit has to be shining on it.

That happens only during the day.

At night the atmosphere starts deionizingand the maximum usable frequency goesdown – and there goes our 10 and 6 meterSkywave Skip.

Which bands provide long distance communication during the peak of theSunspot cycle?

6 and 10 meters. (T3C-12)

What is generally the best time for long distance 10 meter propogation via the FLayer?

From dawn to shortly after sunset during periods of peak sunspot activity (T3C-09)

There is Also Another Way to Catch a Break

There is a lower layer of the atmosphereThat can be ionized for short periods ofTime and will reflect 6 or even 2 meterFrequencies back to earth.

It is called the E layer and its sporadicIonization is called sporadic E.

It particularly effects 6 meters. SuddenBand 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 andno plans to use 6 meters.

Related Question

Which type of the following propagation types is most commonly associated withStrong over the horizon signals on the 10, 6, and 2 meter bands?

Sporadic E(T3C-04)

Do note that sporadic E is not a worldWide reflecting layer in the atmosphereSo the places that “open up” are selectiveNot only in when it happens but where.

The magic band (6 meters) often likesSouth America – good for our bilingualmembers but not a particularly goodroute for reporting emergency informationaround the ward or stake.

Getting Atmospheric Reflection with Lucky Shots

Meteor Scatter

Meteors leave an ionization trail behind themthat can be used to reflect radio signals –especial 6 meters (the Magic Band)

Which band is best suited for communicatingvia meteor scatter?

6 meters(T3C-07)

Another Lucky ShotAuroral ScatterThe northern lights are atmospheric ionization.Not surprisingly we can bounce radio signalsoff them.

Unfortunately, signals bounce all over in thepretty, but messy ionization area. The resultis signals very in strength and are oftendistorted.

What is a characteristic of VHF signals receivedby auroral reflextion?

The signals experience rapid fluctuations of strength and are often distorted.(T3C-03)

Getting Your Ducts in a Row

Normally airTemperature getsLower the higherYou go in theAtmosphere.

In a temperature inversion you get cold air on the ground and a warmlayer above. Air pollution people hate them – but they create opportunity forlong distance radio communication in VHF and UHF bands.

What Does a Temperature Inversion Do for Radio

Plan A – the change in air density ofthe warm air above bounces thesignal back down to the ground, whereit may bounce back up again.

Like a ball bouncing on the ground –bounces weaken signals with eachbounce.

Plan B – the signal gets in the warm layer andBounces between cold layers – lot less energyLoss.Catch – it skips everything in between andComes at an unknown spot on the other end.

What causes tropospheric ducting?

Temperature inversions in the atmosphere(T3C-08)

Problems for Emergency Communication

Simplex radio to radio willAlways work if the two radiosAre still in tact.

Repeaters may or may notBe running.

Sporadic E, meteor scatter,And tropospheric ducting areNot reliably available.

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 UHFCommunications to ranges of about 300 miles on a regular basis?

Tropospheric Scatter(T3C-06)

Bounce the radio signal off ofParticles in the lower atmosphere

You’ve seen these particlesat work when you watchstars twinkle at night.