Waves & The EM Spectrum

Radio theory, antenna theory, electromagnetic propagation - all are advanced, complicated topics.  I'm going to keep it short and sweet and try to cover only what you need to know to intelligently choose, install, and operate a race car comms system.  But we do have to cover a bit - because if you don't know a wavelength from a frequency, or UHF from VHF, you're going to be at a bit of a disadvantage. We'll start with some basic wave form physics and the electromagnetic (EM) spectrum - don't worry - it's mostly harmless.

Two-way radios (that is, radios that can transmit and receive, allowing you to communicate) work by transmitting and receiving radio waves.

Radio waves are a form of electromagnetic energy that are generated by one radio, transmitted by that radio's antenna, travel (or propagate) through the air, are intercepted (received) by another radio's antenna, and can then be heard on the receiving radio.

The following diagram depicts many different types of radio waves and their uses.

Waves transfer energy from one point to another without transferring matter. They consist of disturbances which transfer the energy in the direction the wave travels without transferring matter.

A radio wave is a very complex form of EM energy containing both electric and magnetic fields that interact in complex ways with the Earth's atmosphere. The study of them is a whole branch of complicated physics. In order to keep this article to a reasonable length, and to keep the appeal as broad as possible, we're going to skip over a lot and just hit some highlights - so no letters from the physicists please!

Properties of Radio Waves

The basic shape of the wave generated by a radio transmitter is that of a sine wave.

A sine wave, as illustrated in this pic, has the following characteristics:

Cycle

A continuous sine wave is composed of several repeating parts called "cycles". Points ABCDE comprise one complete cycle having a maximum value above, and a maximum value below, the reference line. The maximum value above the line is referred to as the TOP or CREST, and the maximum value below the line is called the BOTTOM or TROUGH, as depicted in the figure. Therefore, one cycle has one crest and one trough.

Wavelength

A wavelength is the distance in space occupied by one cycle of a radio wave at any given instant. If the wave could be frozen in place and measured, the wavelength would be the distance from the leading edge of one cycle to the corresponding point on the next cycle. Wavelengths vary from a few hundredths of an inch at extremely high frequencies to many miles at extremely low frequencies; however, common practice is to express wavelengths in meters. The distance between A and E is one wavelength.

Amplitude

Two waves may have the same wavelength, but the crest of one may rise higher above the reference line than the crest of another. The height of a wave crest above the reference line is called the amplitude of the wave. The amplitude of a wave gives a relative indication of the amount of energy the wave transmits - in other words the signal's strength..

Frequency

When a continuous series of waves passes through a medium (like air), a certain number of individual waves pass a given point in a specific amount of time. The number of cycles of a continuous wave per unit of time is called the frequency of the wave and is measured in Hertz. One Hertz (abbreviated Hz) is one cycle per second. Therefore, if 5 waves pass a point in one second, the frequency of the wave is 5 cycles per second or 5 Hz.

One frequency with which we are all familiar is the frequency of normal household electrical current. In North America, this is 60 Hz.

In the study of radio waves, the frequencies can get very high, so in addition to Hz we also use the units kilohertz (one thousand hertz) megahertz (one million hertz), and gigahertz (one billion hertz).

1,000,000 Hertz (Hz) = 1000 kilohertz (KHz) = 1 megahertz (MHz) = 0.1 gigahertz (GHz).

Frequency and wavelength are related to one another by the following simple equations:

frequency = speed of light / wavelength

and

wavelength = speed of light / frequency

where  the speed of light = 299 792 458 meters / second  (roughly 300 million m/s )

Most often we talk about radio waves by frequency. A quick and dirty method to approximate the wavelength of a given radio frequency is to divide 300 by the frequency in MHz to get the wavelength in metres.

For example, if Race Ops transmit on a frequency of 151.490 MHz, the wavelength of their transmissions is 300 / 151.490 = 1.980 metres (or about 2 metres).

The following diagram illustrates waves with the same amplitude, but different wavelengths and therefore also different frequencies:

Frequencies between 3000 hertz (3 KHz) and 300,000,000,000 hertz (300 GHz) are called radio frequencies since they are commonly used in radio communications. This part of the EM spectrum is divided into bands, each band being 10 times higher in frequency than the one immediately below it. The radio frequency bands are shown in the following table.

Radio Frequency Bands

Here's a look at where these radio frequencies fit in the overall EM spectrum.

Why is all this talk of wavelength and frequency important?

Well, for the average user, it comes down to two things - range and clarity.

That is - how far can I reach with my radio?  And how clear will it be?

The answers to these two questions depend on a lot of complicated inter-related factors - from power to antenna tuning to sun-spot activity and the curvature of the earth.

But, the factors we can easily control that most affect range and clarity are wavelength (and therefore the frequency) and the power output of the radio.  We'll cover these in more detail as they apply to choosing and buying a radio in a moment, but first we must briefly introduce the concepts of theoretical range, attenuation, and "line of sight".

The wavelength of the radio wave has a huge effect on the range and clarity that can be achieved. In very simple terms, the longer the wavelength, the lower the frequency, and the greater the range. The physics behind why this is so are not terribly important to understand so we'll just accept it as fact.

If it helps, imagine you have a rope between two people which you intend to use to send a signal between them. Imagine you intend to send that signal by flicking one end of the rope so as to send a wave down it.  The longer the rope, the further your signal can reach, but the weaker it will be when it gets there (poorer quality). There's all kinds wrong with that analogy, so to keep me from going on for pages and to keep the physics boffins off my back, just remember that in general:

lower frequency = longer wavelength = greater range.

In the typical "nothing is free" nature of the universe, typically the longer the wavelength the poorer the quality of the signal and therefore the less clear it is. Think of a movie where you've seen military radio operators communicating over great distances, particularly over the horizon from one another (also known as "beyond line of sight or BLOS). The reception is spotty and full of static. There are delays, interference, and lots of "noise". Quality is poor and the operators speak in that funny sounding strict military way to make sure they are heard and understood. This is because, in order for the radio waves to transmit that far, they have to be long wavelength (low frequency) - typically in the HF range.

Now, imagine a modern cellphone operating in the GHz frequency range - very short wavelength, very high frequency. Quality and clarity is excellent, but range is very poor - which is why you have to be within range of a "cellphone tower" to have service, and why the towers must be so high.

So now we have:

lower frequency = longer wavelength = greater range but poorer quality.

Which brings us to the concept of "line of sight" range. What this means is that, theoretically, for radios that operate in the frequency range we are interested in (typically VHF and UHF), quality is very good, but because of the short-ish wavelengths, range is limited to direct line of sight (LOS) - that is, there must be an unobstructed path directly between the transmitting antenna and the receiving antenna. The direct LOS for two objects on the surface of the earth, providing there are no obstructions between them, is about 5 miles before the curvature of the earth gets in the way and begins to obscure one from the other. This is where antenna height comes into play - just like for the cell tower. It is easy to imagine that LOS is going to be a lot further if two people were perched at the top of two mountains than if they were sitting on surfboards on the ocean. On land, in other terrain, obviously this theoretical LOS range can very from several miles to mere feet.

The following diagram illustrates the concept of LOS transmission and the advantage of antenna height.

The equation for max theoretical range is:

R = 1.4*(Sqrt(Ht) + Sqrt(Hr))

Where:

R = the range in miles

Ht = the height of the transmitting antenna in feet

Hr = the height of the receiving antenna in feet

So if your antennae are 6' off the ground, max theoretical range is about 1.4*(Sqrt(6) + Sqrt(6) = 6.8 miles

But if they are 500' off the ground, max range increases to: 1.4*(Sqrt(500) + Sqrt(500) = 62 miles (assuming there are no obstructions).

That's the theoretical maximum range.

In practice, the propagation characteristics of these radio waves vary substantially depending on the exact frequency and the strength of the transmitted signal (a function of both the transmitter and the antenna characteristics).

In reality, there are factors that can both add to and subtract from this range. Factors that reduce the range include:

• Signal attenuation. This is a fancy way of saying, the farther a signal goes, the weaker it gets. Attenuation can be by absorption, reflection, or refraction of the radio wave energy.
• Interference. The atmosphere is FULL of EM waves of all kind - the more there are in the area the radio is being used, the more interference there is and the poorer the range and quality of transmission and reception.

Factors that increase range include:

• The ability of radio waves to penetrate through or bend around certain obstructions.
• The power output of the radio - the greater the power the less the attenuation of the waves.
• Antenna height - obviously the taller the transmission and reception antennae, the greater the range.

The different radios we can buy and use are susceptible to these factors to a greater or lesser degree depending on the radio, and we'll cover how shortly.

Of course, there are reasons other than these that may influence or even wholly dictate the choice we must make in terms of radio frequency band - chiefly what frequency do we need to use to be able to communicate with others?

Once a radio that works in a particular frequency band is chosen, the key to getting more range is to either raise the height of the antenna, increase the power of the radio, or both.

Two-way Radio Basics

OK, so we've covered the basics of radio waves so that we can now cover the basics of two-way radios - like those used used in off-road race cars.

We're all familiar with the type of radio we have in our daily driver cars. They operate using the same radio waves as we have described above. The difference is, they are receivers only - they receive the radio waves transmitted or "broadcast" by the radio station (which, for reasons we now understand, use tall antenna towers and high power). But they cannot transmit - so not very useful for two-way communications.

A two-way radio, on the other hand, can both transmit and receive.

Generally, two-way radios (hereafter referred to simply as "radios") , come in one of three flavours:

• Hand-held (what we called walkie-talkies when we were kids)
• Mobile (like a CB radio in a truck, a police-car radio, or indeed a racecar radio)
• Stationary or "base station" models that are intended to be permanently installed in a fixed location (like the police or taxi dispatcher's radio)

They all work the same way, but as we progress from hand-held up to stationary size, weight, power, and antenna size increase (and therefore range). Clearly, each has its specific purpose. The rest of this article shall concentrate on hand-held and mobile models as these are the most useful to racers (even your "camp" or pit is rarely truly stationary).

If you've ever used a CB radio or a walkie-talkie then you're already familiar with the basic features and method of operation of a race radio - they work in essentially the same way.  Common features include:

• A method to select the frequency on which to transmit and receive (often in the form of selecting a preprogrammed channel, as with a CB radio).
• A microphone to speak into.
• A press-to-talk (PTT) switch to activate the microphone and send a transmission.
• A speaker or headphone connection so received signals can be heard.
• A power amplifier to amplify transmitted and received signals.

Handheld portable radios are designed for short-range communication between people or between a person and a mobile radio. They prioritize portability over range and therefore have small antennae and limited battery power. In the United States the Federal Communications Commission regulations state that handheld radios are limited to no more than 5 watts of power.

Vehicle-mounted mobile two-way radios mount in a car or truck and are wired into the vehicle's electrical system for power. They have greater power and a larger external antenna mounted on the vehicle. Power is normally in the 50-100 watt range for a typical race radio.

Desktop base station radios use wall AC power and an external-mounted antenna, often mounted on top of a building or even on a tower to increase range.

Mobile radios can be used as base-station radios by connecting them to a convenient DC power source (a spare car battery) or by using an AC to DC power converter.

Modulation and Transmission

OK, so radios use amplifiers and antennae to transmit electromagnetic energy (radio waves) back and forth through the atmosphere. But how does this let me talk back and forth with another radio user, and why do I care how it works.  The answer to the second question is, because you have to know what type of radio you need - and one of the main differences between radios is something you're already familiar with - some are AM, some are FM, just like the radio in your daily driver car. We need to understand the difference between AM and FM for one of two reasons. Either:

• We need to decide which is best for our intended use and therefore which to buy, or
• If the type is already decided for us by the other users we will be communicating with (as is the case at a race), we need to understand how this type works so we can maximize its strengths and minimize its weaknesses (as well as troubleshoot problems with our radio).

And to understand the difference between AM and FM, we must first understand what modulation is (that's what the "M" in AM and FM stands for).  And understanding modulation is the answer to how a radio actually lets you talk back and forth.

Here's the super quick and dirty version of how it all works.

Sound, produced by your voice (or your home theatre speakers), consists of physical vibrations in the air. If you could see the actual air molecules, you would see that they alternately bunch up together (a compression) and get spread out (a rarefaction).

These are sound waves, created by the movement of your vocal chords, a stereo speaker's cone, or anything else that can compress air and therefore create sound.

These sound waves also have frequency - ranging from 20Hz (deep bass) to 20 kHz (high treble). Human speech occurs in the 80Hz - 3 kHz range.

In the case of simple communication through normal speech and hearing, one person's vocal chords create the sound waves, they travel through the air and vibrate the listeners eardrum back and forth which turns the sound waves into impulses the brain can read. Simple.

When we introduce a radio to extend the range of communication, things get a little more complicated.

Now, when the speaker speaks, the sound waves they create vibrate not an eardrum, but a thin membrane in the microphone. The microphone translates these vibrations into electrical impulses. These electrical signals are the sound, called the "information", that needs to get carried to the speaker of the radio on the receiving end so that they can operate in reverse and cause the speaker cone to vibrate back and forth, creating sound waves again, that then go on to vibrate the listener's ear drum.

The "information" we want to send via radio (e.g. someone's voice) is called the baseband signal.

So we have information that needs to be carried somewhere. This is where modulation comes in.  Just like a letter needs a postman to carry it to its destination, so the sound information needs a carrier to carry it to the receiving radio. Only instead of using a guy with a mail bag, we use electromagnetic energy waves - radio waves.

With me so far?

Good.  This is where modulation comes in. Modulation is simply a fancy word for changing something in order to encode it with information. In this case, modulating a carrier wave so that it is encoded with a baseband signal (sound information) that can be demodulated at the receiving end and the information, or sound, decoded and sent to the speaker and thence the listener's ear.

A simple form of modulation is to think of a pen drawing a straight line across a piece of paper. The straight line is unmodulated, it carries and transmits no information.

However, if you modulate (change / vary) the line by writing, then the line carries and transmits information.

Back to radios.

Recall that radio waves have both frequency and amplitude.

Radio waves, like other waves, are measured by frequency, the number of times a wave varies above and below a reference point.

In addition to frequency, radio waves also have amplitude. Amplitude describes the height or intensity of a given wave.

The ability to manipulate variations in amplitude and frequency makes possible the modulation of the carrier radio wave. In other words, we modulate, or change, the frequency or the amplitude of the carrier wave, and by doing so we can code it with the information, (baseband signal) we wish it to carry.

Thus, we have AM or "amplitude modulation" radio and FM or "frequency modulation" radio waves.

AM vs. FM

AM (amplitude modulation) varies the amplitude (intensity) of the carrier, while the frequency remains the same.

FM (frequency modulation) encodes the sound information by changing the frequency, while the amplitude remains constant.

This figure shows a simple baseband or signal sine wave, followed by a representation of what it might look like modulated by amplitude and by frequency, (AM and FM).

Each method has its advantages and disadvantages, with one of the most important differences being the amount of bandwidth the chosen method consumes in the process. That is, how much of the EM spectrum is need to convey the modulated signal that consists of the combination of the information (the baseband signal) and the carrier signal.

A precise description of the different modulation methods is beyond the scope of this article, so I'll just summarize some of the important differences. Keep in mind that these are generalizations and not absolutes.

AM is the oldest and simplest form of modulation. AM is a well established and mature technology. AM is easy to generate, easy to demodulate, and consumes less bandwidth than FM. It can be done using low power and relatively cheap and simple equipment.

However, AM is very sensitive to noise contamination (noise is any EM signal that is not wanted - like static). Because AM transmission varies the amplitude of the wave, and static interacts with the amplitude of radio waves, AM is more susceptible to interference from other EM energy which further contributes to reduced quality and reduced fidelity of the sound. That's the scratchy, crackly part of AM radio on your car stereo.

AM is also limited by regulation and industry practice in that it is generally used for lower frequency transmissions - which means it generally has longer range than FM, but because of the resulting lower bandwidth allocated, isn't able to send as much information. That is, AM is unable to carry the full range of frequencies needed to reproduce high fidelity sound like music. Ever notice how most AM radio stations are all news, talk or sports (or really crappy music)? This is less of a problem with voice-only radio as in two-way radio use.

FM is far more complex than AM. This means it requires more complex and expensive equipment (the modulation and demodulation are far more complex). Because the frequency is being changed, an FM signal consumes much more bandwidth than an AM signal - on the order of 10 to 20 times more. This greater bandwidth has its own pluses and minuses. On the plus side it means FM can support the transmission of more baseband frequency components, i.e. more information, higher fidelity sound. For example, commercial FM radio stations are each allocated a 180 kHz bandwidth which allows them to support a maximum baseband frequency of 15 kHz. On the other hand, commercial AM radio stations are each assigned to a 10 kHz channel which only allows them to support a maximum baseband frequency of 5 kHz. Recall that human hearing ranges from 20Hz to 20KHz and we see that better sound can be heard on FM (although voice-only communication doesn't really suffer from AM's lack of bandwidth). On the down side it also means that FM channels must be "wider" and therefore there are fewer of them in a given block of the EM spectrum (which can be a problem in the highly congested EM spectrum of today).

By regulation and industry practice, FM transmissions are often (but not always) at higher frequencies (VHF & UHF) than their AM counterparts (HF & lower VHF) and thus even more limited to line of sight ranges than AM.

Although more complex in design, FM offers better resistance to the effects of noise since it varies the frequency of the signal keeping the amplitude constant and therefore the modulation is not as susceptible to interference or being distorted. When a radio has more signal and less noise, we say it has a better signal-to-noise ration or greater SNR (you may have seen this term in radio or stereo specs). Ultimately, because of its greater bandwidth and better SNR, FM generally produces higher quality signals and therefore better quality sound.

This following table illustrates a summary of the differences between AM and FM.

* - these characteristics are not strictly due to the modulation method alone, but are due to the frequencies commonly used with the type of modulation by convention, government regulator assignment, standard OEM design, or law.

Two-way radio frequencies

So, we've already touched on different frequencies. Let's take a brief look now at more specific radio frequencies.

Two-way radios can operate on many different frequencies, and these frequencies are assigned differently in different countries.

Typically different frequencies are "channelized"  - that is, a specific frequency is assigned a fixed channel number for a given type of radio, so that operators need not tune equipment to a particular frequency but instead can use one or more channels pre-set with the frequency, easily chosen by a push-button or other means. It is, for instance, easier to remember "Channel 1" than to remember "26.965 MHz" (CB Channel 1) or "156.05 MHz" (Marine channel 1). It is, of course, necessary to identify which radio service is under discussion when specifying a frequency by its channel number.

This is a list of international Maritime channels

The performance of a radio system is partly dependent on the characteristics of the frequency band used. The selection of a frequency for a two-way radio system is affected, in part, by:

• government licensing and regulations.
• local congestion or availability of frequencies or channels.
• terrain, since radio signals travel differently in forests and urban environments
• the presence of noise, interference, etc..
• in the US, some frequencies require approval of a frequency coordination committee.

This chart depicts frequency allocations in the United States.

Note how incredibly "crowded" the EM spectrum is!

Each country allocates radio frequencies to different two-way services, in accordance with international agreements. In the United States some examples of two-way services are: Citizen's Band (CB radio) , FRS, Marine, etc.

This is an excellent article on frequency allocations.

The following chart depicts some popular two-way radio services and their frequency allocations.

150 - 162 MHz:  FM @ 15 kHz steps

     150.815 - 150.965  Auto Emergency

     150.995 - 151.595  Highway / Forestry / Industry

     151.625 - 151.955  Business                      (30 kHz steps)

     152.030 - 152.240  Mobile phone (Base) / Page    (30 kHz steps)

     152.270 - 152.450  Taxi (Base)

     152.510 - 152.840  Mobile phone (Base) / Page    (30 kHz steps)

     152.870 - 153.725  Industry

     153.740 - 154.445  Fire / Govt (mobile)

     154.452 - 154.482  Industry (telemetry)          (7.5 kHz steps)

     154.490 - 154.625  Industry

     154.650 - 156.240  Police / Govt / Emrgncy / Hwy

     156.025 - 157.425  Maritime (ship)               (25 kHz steps)

     157.470 - 157.515  Auto Emergency

     157.530 - 157.710  Taxi (mobile) / Business

     157.770 - 158.100  Mobile phone (mobile) / Page  (30 kHz steps)

     158.130 - 158.460  Industry

     158.490 - 158.700  Mobile phone (mobile) / Page  (30 kHz steps)

     158.730 - 159.210  Police / Govt / Highway

     159.225 - 159.465  Forestry Conservation

     159.495 - 160.200  Transportation - bus, truck

     160.215 - 161.610  Railroad

     160.625 - 160.950  Maritime - Coast              (25 kHz steps)

     161.640 - 161.760 {Broadcast Pickups

     161.500 - 162.025 {Maritime - Coast              (25 kHz steps)

UHF versus VHF

The two frequency bands most commonly used for two-way radios of the type we are interested in are VHF and UHF.

Neither frequency band is inherently better than the other. Both formats are effective ways to communicate with another person so the right radio depends on the application.

As we have learned, the frequency also determines the wavelength, and the wavelength has a big impact on radio performance.

While both VHF and UHF are "line of sight" radios in theory, anyone who has used a two-way radio knows that in practice, it is possible to communicate with someone you can't see. The exact reasons are very complex, suffice to say that radio waves can penetrate certain solid barriers, they can also bend around obstacles, and "find there way through" obstacles (like trees) that are tightly spaced but not solid. How effectively they do this is largely a factor of the wavelength. Of course, greater power increases range for any wavelength, to a point (as does a properly sized and tuned antenna).

VHF has a longer wavelength and as a general rule a VHF radio signal travels a greater distance. Lower frequencies (or longer wavelengths) have greater penetrating power.

On the other hand, UHF has a shorter wavelength which makes it easier for the signal to find its way through rugged terrain and around obstacles.

Imagine we are separated from the radio we wish to talk to by some mixed terrain with rocks and trees. Imagine the gaps between the trees are 3 feet wide. Imagine we are using a VHF radio transmitting a wavelength of 5 feet, and UHF radio transmitting a wavelength of 1.5 feet. The longer VHF wave will penetrate the trees and rocks better, but will not find its way through the trees as well since the wavelength is longer than the gaps between the trees. On the other hand, the UHF radio will have less penetrating power to get through the trees and rocks, but the signal will find its way around the trees and obstacles better since it is less than the gap between the obstacles. Imagine the wavelength is like a 2x4 strapped across your shoulders - if it's 5' long you can't fit between the trees, but if it's only 1.5' long, you can. Remember, both signals attenuate (loose strength) the further they go, and the more obstacles they encounter and get reflected off, refracted (bent) off, and absorbed by.  Now, in a different scenario, imagine there are obstacles such as large boulders that are about 3 feet in diameter. Since they are larger than the UHF wavelength, they will block the UHF signal when it encounters them. Conversely, the larger 5 foot VHF wavelength, being larger than the boulders, will get around them better. 

The shape and composition (density) of obstacles have a large affect on how radio waves interact with them too. Smooth, rounded objects tend to deflect signals, whereas flat surfaces tend to reflect or absorb them. Dense materials such as metal tend to reflect signals, less dense material such as wood tend to absorb signals or let them pass, depending on the wavelength and power of the transmission.

However, if a VHF wave and a UHF wave were transmitted over an area without barriers, the VHF wave would travel almost twice as far.

There are more available channels with UHF so in more populated areas UHF may be less likely to have interference from other systems. Since the range of UHF is also not as far as VHF under most conditions, there is less chance of distant radios interfering with your signal.

One other advantage of the short wavelength that is produced by the higher UHF frequency is that the antenna on the radio can be shorter than an equivalent VHF radio. That can make it more convenient in certain installations or to carry around as a portable radio.

Since VHF has been around longer and isn’t as complicated to make, equipment can be cheaper when compared to similar UHF equipment.

Simplex versus Duplex

One last thing we should discuss because you may come across it when researching radios is the difference between simplex and duplex operation.

Simplex systems use a single frequency (channel) for both transmit and receive. This means you can't transmit and receive simultaneously - in other words, you can't talk and listen at the same time - you have to be doing one or the other.  Most often, a push-to-talk (PTT) switch is activated to transmit, and then released when you want to listen. This is also known as "keying the mic"(rophone) when you want to talk. The thing is, whomever you're communication with has to do the same, in coordination with you. That is, if you both key the mic and try to talk at the same time neither of you will hear the other. This situation is handled by the use of certain "pro words" such as "over" so that both parties can work in sync.

A duplex system, on the other hand, transmits and receives on different frequencies. A half-duplex system still requires the use of a PTT switch and operates much the same as a simplex radio. A full-duplex system however can both transmit and receive simultaneously and no PTT switch is required. Your average household telephone is duplex - you can talk and listen at the same time, so conversation can be more "natural" and less "formal". Duplex radio systems are expensive,complicated, and not of further interest to us here, although you may come across the term.

Transceivers and 'Nets

Three last terms:

Because "two-way radio" is a bit of a mouthful (and frankly a little 1950's sounding) and because two-way radios both transmit and receive, it is common to refer to them as "transceivers". This is a cool word, and technically accurate, but a bugger to consistently spell correctly, I often just use the term "radio".

A "network" or "net" is the term used for a group of radios communicating on the same frequency (or channel). There may be any number of users on a net and there may be several nets established at any given event or race. For example, there may be a "main" net, a coordination net, a safety net, etc. You will see the term used in lots of different ways, for example "get on the net and call ops" meaning "Please select the appropriate channel on the transceiver and depress the push-to-talk switch in order to initiate two-way voice communications with the members of our race team who are manning the main pit stop location"; or "listen out on the net" meaning "Please select the appropriate channel on the transceiver and monitor the radio's speaker/headphones in order to hear transmissions being made on this frequency by other parties."  The net is also sometimes referred to as the "circuit".

Individual users operating on a net are often referred to as "stations". We'll see this term used later when we talk about radio voice procedures and how to talk like a pro on the net.

OK, so that's about enough theory. Let's get down to business.

Race Radios

Depending on the race series or sanctioning body, offroad race radios need to be capable of operating in the 150-158 MHz VHF FM band.

Here are the services assigned to this range of frequencies in the US:

• 148-150 Land mobile, fixed, satellite
• 150–156 MHz: "VHF Business band," the unlicensed Multi-Use Radio Service (MURS), and other 2-way land mobile, FM
• 156–158 MHz VHF Marine Radio; narrow band FM, 156.8 MHz (Channel 16) is the maritime emergency and contact frequency.
• 160-161 MHz Railways
• 162.40–162.55: NOAA Weather Stations, narrowband FM

My race team, Joint Force Racing, sources all our comms needs from Rugged Radios in San Luis Obispo, California.

Here's a look at the components of the Joint Force Racing offroad race team comms setup.

1. VOL/PWR Knob
   This knob is turned clockwise to turn the radio on and to increase the volume. It is turned counterclockwise into the click-stop to turn the radio off.
2. Microphone Jack
   The microphone plug connects to this jack.
3. [P1] - [P4] Buttons (Programmable Function Buttons)
   Because of the wide range of users and their different needs combined with the large number of features of this radio, the keys are all fully programmable (i.e. they do not have fixed functions.) The function of these keys is programmed by the dealer (i.e. Rugged Radios) according to your needs and use. For example, these buttons can be set up for special applications, such as High/Low power selection, Monitor, Talk-Around, etc., as determined by your requirements. Later on I will show the standard features Rugged Radios programs.
4. [▲]/[▼] Buttons (Programmable Function Buttons)
   In the factory default, pressing either button changes the current channel (and displayed channel number or name). Holding down either button for more than 1.5 seconds causes the radio to begin stepping (repeatedly) upward or downward through the channels. These buttons can also be programmed for other functions by Rugged Radios.
5. LCD (Liquid Crystal Display)
   The display includes a 8-character alpha-numeric section showing Channel name tags/identity information and error messages, and an upper icon row displaying feature status (see below).
6. TX/BUSY Indicator
   Indicates transceiver’s Transmit/Receive Status as follows:
   Steady Red: Transmitting in progress
   Steady Green: Signaling Off
   Blinking Green: Busy Channel/Squelch Off

1. 13.6V DC Cable Pigtail with Connector
   The supplied DC power cable must be connected to this 2-pin connector. Use only the supplied, fused cable, extended if necessary, for power connection.
2. Antenna Socket
   The 50-Ohm coaxial feedline to the antenna must be connected here, using a type-M (PL-259) plug.
3. D-Sub 15-Pin Accessory Connector
   External TX audio line input, PTT (Push To Talk), Squelch, and external RX audio line output signals may be obtained from this connector. This is done when integrating the radio into an in-car comms setup that includes PTT switches, helmet speakers, and an intercom system. We'll go over this in detail a little later.
4. External Speaker Jack
   An external loudspeaker, headset, or helmet-mounted speakers may be connected to this 2-contact, 3.5-mm mini-phone jack. Caution: Do not connect either wire of this line to ground, and be certain that speakers have adequate capability to handle the audio output (12 W) from the radio.

Radio Operation

Because of the huge number of features and possible programmable button combinations, I'm not going to detail every aspect of operating the radio, but will cover the basics.

The following is a composite image of all possible indication that can be shown on the LCD display:

Channel Programming

As discussed, radios of this type are preprogrammed by dealers like Rugged Radios so that certain specific frequencies are assigned channel numbers and then the user selects a channel for operation rather than setting an actual frequency. For some professional radio users, like military personnel, this can seem odd as they are used to using equipment where controls are used to set a specific frequency by selecting that actual frequency in kHz or MHz. But for most users, using channels is much more simple.

However, before Rugged ship you a radio, they also program it with a "standard" set of frequencies and channel names. For example, for Ultra4 / King of the Hammer's racing, commonly used frequencies include (in MHz):

151.490 - KOH Race Ops – Used internally to maintain control of the race.  Also the main channel for the helo.

151.715 - KOH Relay – Used by the checkpoints to radio in their times.  Also general channel monitored by Wild Bill (BFG Relay)

157.450 - KOH Medical – Used by ambulances, security, and recovery crews in resolution of emergency.  Racers or fans would report emergencies on KOH Relay. 

153.395 - BFG Pits – For racer to radio ahead to the BFG pits to let them know what they need.

Other common frequencies in offroad racing include:

151.625 - Weatherman
151.715 - BFG Relay / SNORE / MORE
154.980 - Baja Pits
151.925 - Checkers
151.505 - Checkers Vegas
153.395 - BFG Pits
153.380 - Mag 7
153.245 - CORE
151.775 - Locos Mocos
151.490 - BITD

WARNING: DO NOT rely on the above listings to have your radio programmed, as they may be subject to change. Check with your race sanctioning body, race organizers, and your radio supplier for current frequencies applicable to your activity.

Which brings me to an important point. I highly recommend buying your comms equipment from a respected dealer involved in the sport, like Rugged Radios, as Matt and the guys will be on site at the event, with their support equipment, able to help you with any last minute programming changes, spare parts, and other tech help.

Here are some basic operations with the radio, using Rugged Radios standard function-key programming:

Additional Components

First, we need a few more things besides the actual radio, namely:

• Helmets with built-in speakers and microphones.
• Antenna
• In-car intercom unit
• Push-to-talk switches
• A hand-held radio for the pit boss.

Helmets

With this measurement in hand, consult the manufacturer's sizing chart. Zamp's chart is as follows:

The sizing chart is a good place to start, but for maximum comfort and protection, a helmet should always be tried on.

Helmets should fit down on top of the head so there is no gap between the helmet and the person's head. The front of the helmet should lay just above the eyebrows for a proper fit. The helmet should not pivot on top of the head, that would mean it's too small. The front of the helmet should not come down over the eyebrows, that would mean the helmet is too large.

The chinstrap should fit snug under the chin. If it is too tight it will cause discomfort and possible choking. If it is too loose it could cause the helmet to slip during a crash and defeat its protection.

Antenna

The antenna is a small but very important part of the system. You will get noticeably better results and more range with your radios with a quality antenna, especially if you place it as high as possible. It is the single most important factor in increasing transmitting and receiving range of a radio. You'll need to make sure you choose an antenna that is specifically designed for the frequencies and application you are using and then choose the best location possible to install it.

Antenna theory is a really complicated subject, and requires a detailed knowledge of wave theory going WAY beyond what we have covered here.

Well, if you ever roll over and break or loose the antenna whip and find that you need to fashion an emergency replacement at the next pit stop - this tells you how long it needs to be.

Recalling the relationship between frequency and wavelength and the rule of thumb, we can calculate that the wavelength, and therefore the length of the antenna whip, since it will be half this (for a half-wave antenna like this)

We simply divide the speed of light in metres per second by the frequency in Hz to get the wavelength in metres.

So, at the upper end of the range we get:

299 792 458 / 174 000 000 = 1.7229 metres

1.7229 metres times 1/2 = 0.86145m or about 2.8 feet.

For those who can't do math in their heads (I'm talking to you Bigelow!), an easier way is to divide 300 by your freq. in MHz, so if your team freq is 150MHz, then 300 / 150 = 2. Wavelength = 2m, therefore 1/2 wave antenna should be about 1m or roughly 3 feet in length!

Wiring & Installation

Basic Voice Procedures

OK, so once you have all your comms gear installed and tested, it's time to learn how to use it like a pro.

I know, I know, I can hear the groans already.

But believe me, there's a reason professional radio operators talk the way we do - and it isn't just to sound cool in the movies! Many of the reasons that aviation, marine, and other professionals speak in the special way they do are equally applicable to a race situation. These include:

• Messages that must get through quickly without delay and be understood the first time.
• The need to be clear and concise on a congested net where many other users must also be able to Tx and Rx.
• The need to be clearly understood even at the edge of your range when quality is poor.
• The need to pass important safety or emergency information and be sure it is received and understood, without having to repeat it.

Due to any number of variables, including radio static, a busy or loud environment, or similarity in the phonetics of different words, a critical piece of information can be misheard or misunderstood if proper procedures are not observed when using two-way radio comms.

The number one rule of talking on the radio is to stay cool and calm, especially in an emergency. Speak normally and don't yell, scream, or rush.

The proper way to communicate via two-way radio is called "voice procedure". Developing good voice procedure is a skill that must be studied and practised, just like any other.

The basics of professional voice procedure are:

DO’s

            -        Listen out before transmitting;
            -        Wait until the net is clear before transmitting;
            -        Know what you are going to say;
            -        Adhere to radiotelephone vocabulary (see prowords below);
            -        Keep transmissions to a minimum;
            -        Keep transmissions short and concise;
            -        Speak in a normal, calm voice.
            -        Avoid idle chatter; and
            -        Be courteous.

DON'T’s

            -        Speak too loudly;
            -        Speak too rapidly;
            -        Whisper;
            -        Make irritating noise into the microphone;
            -        Cut in when others are transmitting;
            -        Hold microphone too close or too far from mouth; and
            -        Blow in your microphone when testing.
            -        Interrupt other transmissions that are in progress.

Remember, you are sharing the net with many other users, so be professional at all times!

Addressing / Callsigns

Because thee are many simultaneous users (stations) on a radio net, you need to "address" your transmissions. That is, you need to make it clear not only to the station with whom you wish to speak, but also to all other stations on the net, who the transmission is intended for. Similarly, when responding to a call or message, you need to indicate who is replying. We do this using "callsigns" which are really nothing more than a short name or nickname that identifies who you are. For example, our racecar callsign is "Car69".  Our main pit crew's callsign is "JFR Ops" (ops is short for "operations"). Our roving pit crew's callsign is "JFR Mobile".  Depending on what net you are using, it is possible to use abbreviated callsigns too. For example, if I'm on the main race channel, and need to talk to my pit crew I would use their full callsign: "JFR Ops" so there is no confusion about to whom I am speaking.  However, if I'm on our team frequency which we may have to ourselves or share with only one or two other teams, I I may shorten the callsign and just call them "Ops".

By convention, the station being called is always stated first, followed by the procedural word (proword) "this is", and then the station calling identifies themself by callsign. For example:

"Car69, this JFR Ops, over".

If you hear your callsign being called, but didn't hear who was calling you, the correct response is to reply using the proword "Station calling", as in:

"Station calling, this is Car69, send, over"

If you need to broadcast a message to everyone on the net, use the callsign "All stations", normally repeated three times, as in:

"All stations, all stations, all stations, this is race control, be advised maximum speed in pit lane reduce to one-zero miles per hour"

Common Calls

The three most common radio calls are the preliminary call, the call answer, and the radio check.

PRELIMINARY CALL

The preliminary call is simply the first or initial call made by a station to initiate a conversation with another station.

The preliminary call is nothing more than the callsign of the called station, proword "this is", callsign of the station calling, and the proword "over". For example,

"JFR Ops, this is Car69, over"

 The amount of traffic on the net and the quality of the comms on the net determine how often a preliminary call needs to be used. For example, if you are on a main net with many users, you would always initiate any exchange with a preliminary call.

However, if you are on your private net, and comms are good quality, you may forgo the preliminary call and just get straight to the message, for example:

"JFR Ops, this is Car69, headed for pit 3, over"

That said, even if you and the station you are calling are the only two users on the net, if comms quality is poor (communications are difficult, broken, etc.) then it is appropriate to begin each exchange with a preliminary call to make sure the station you are calling is ready to receive your message. This is particularly true if you need to send a long message they will have to write down.

CALL ANSWER

The call answer is simply the initial response by a called station to a preliminary call addressed to them.

When you are called by another station you will hear their preliminary call, your response is the call answer which is simply: the callsign of the station calling, proword "this is", callsign of the station being called, and the proword "over". For example:

Preliminary Call - "JFR Ops, this is Car69, over"

Call Answer - "Car69, this is JFR Ops, over"

Before transmitting a call answer, make sure you are ready to receive (copy) the caller's transmission.

If you are not ready, or are otherwise occupied, immediately answer and tell the calling station to wait or standby (see applicable prowords and voice procedures below).

RADIO CHECKS

Performing a radio check before launching on a mission...errm, I mean starting a race or pre-running session is critical. Do not skip it. The radio check serves to:

• Determine the serviceability of your equipment
• Determining the circuit conditions.

The former is obvious, but the latter is also important as it determines "message transmission speed" (i.e. how fast you can speak on the net), along with how strict your voice procedures need to be, how long or formal your callsigns need to be, etc. While I always advocate for strict voice procedures and utmost professionalism at all times on any net, I recognize that not everyone shares my passion for procedure. However, if the net is congested, noisy, or otherwise poor quality, it is to your utmost advantage to be strict with your voice procedures as this will enable you to communicate as clearly and effectively as possible with as little repetition as possible. Remember, this is very important because the net is not yours - it is a shared resource. Good procedures will help you avoid "stepping on" other people's transmissions, clogging the net with garbage talk, and otherwise pissing off your fellow racers who are also trying to communicate in challenging conditions.

So do your radio checks, mmmkay.

Now, "Hey Bubba, you got ya ears on?" is NOT a proper radio check!

A radio check is initiated by one station as follows: station being called, proword "this is", callsign of the station calling, proword "radio check", and the proword "over". For example:

"JFR Ops, this is Car69, radio check, over"

The correct response to a radio check is a report of strength and readability, as follows:

Report Of Signal Strength

1. Fading - At times, your signal strength fades to such extent that continuous reception cannot be relied upon
2. Very Weak - I can hear you only with great difficulty
3. Weak - I can hear you only with difficulty
4. Good - Your signal is good.
5. Loud - Your signal is strong.  Interference will not bother my copying

Report Of Signal Readability (clarity)

1. Unreadable - Quality bad, I can’t read you
2. With interference - I have trouble reading you due to interference
3. Intermittent - I have trouble reading you because your signal is intermittent
4. Readable - Quality good, I can read you
5. Clear - Excellent quality

Therefore, a complete radio check would be:

"JFR Ops, this is Car69, radio check, over"

"Car69, this is JFR Ops, loud and clear, how me?, over"

"JFR Ops, this is Car69, loud and clear, out"

Technically, signal strength and readability can be reported in any combination (but always in the order strength then readability), but obviously certain combinations don't make sense. For example, you're unlikely to hear "very weak and clear".

Note that both scales are numbered from one to five, where one is the worst and five is the best. It is therefore possible to report a radio check by number instead of prowords, in which case the numbers are separated with the word "by". For example "Five by five" is the numerical equivalent of "loud and clear".

Personally, I don't favour this method, as the numbers don't immediately convey the information required and you have translate them into the words in your head to understand something meaningful. For example, 3 x 2 doesn't mean a lot to me intuitively, but "weak with interference" does.

Finally, it is perfectly acceptable to simply substitute the proword "roger" for "loud and clear", in which case the above full radio check can be abbreviated to:

"JFR Ops, this is Car69, radio check, over"

"Car69, this is JFR Ops ,roger, over"

"JFR Ops, this is Car69, roger, out"

Prowords

The foundation for developing professional voice procedure is the use of certain special words or phrases, called "prowords". This is the "radiotelephone vocabulary" referred to in the previous list of "DO's". Use these prowords to communicate clearly, effectively, and quickly.

Basic Prowords

Phonetic Alphabet

The phonetic alphabet is used to spell words using a unique, easily distinguished word to represent each letter of the alphabet. This is done to reduce the chance for misunderstanding and reduce the need to repeat things since audio quality may be poor and many letters can easily be confused with others.

The phonetic alphabet is as follows:

Relaxations

Depending on the net in use, the number of stations on the net, the quality of the circuit, and the tactical situation (how quickly you need to transmit and receive, it is possible to relax from full formal voice procedures. For example, if the net is very busy, brevity and speed are usually the chief concerns and some risk of loss of clarity can be accepted. If, on the other hand, the net is not busy but ranges are long, quality poor, and information critical, then more formal procedures are called for.

The following examples demonstrate three different levels of formality used in sending the same message, which is the pit crew asking what time the car will be at pit stop two and the car replying.

Formal:

• Car69 this is JFR ops, over. 
• JFR Ops this is Car69, send, over
• Car69 this is JFR ops, interrogative, say ETA Pit 2, over.
• JFR Ops this is Car69, ETA Pit 2, 12:15 hrs, over
• Car69 this is JFR ops, ROGER, OUT.

Relaxed:

• Car69 this is JFR ops, over.
• 69, go ahead
• 69 send ETA Pit 2, over.
• Ops, ETA Pit 2, 12:15 hrs, over
• 69, copy that.

Super relaxed:

• 69, ops
• Ops, 69, go
• 69 say ETA Pit 2, over.
• Ops, ETA 12:15, over
• Ops copies

USING MAYDAY TO TRANSMIT A DISTRESS CALL

Aircraft and ships use a standardized method of transmitting a distress message that enables the maximum amount of information to be conveyed in the shortest time possible. It also enables distant stations to receive and understand the information, even when clarity is low. Now, in the case of aircraft and ships at sea, this is extremely important as it may be the last anybody hears from them until (if) a search and rescue party is able to locate them.

Things are probably not so critical in offroad racing, but then again, if you're lost and alone in the desert, it's probably a good idea to communicate in a proven, professional manner. Using procedure also helps to keep you calm in stressful situations so you don't end up yelling or rambling incoherently into the mic and not helping yourself.

The distress call consists of:

• The distress signal "MAYDAY" spoken three times;
• The proword "THIS IS";
• The identification (callsign) of the station in distress spoken three times.
• Position (or estimated)
• Time;
• Nature of emergency; and
• Your intentions (remain with vehicle, walk towards camp, etc.)
• Over

Example:

"Mayday, mayday, mayday, this is Car69, Car69, Car 69. Position race mile 63, Time 15:30 local, Car overturned and on fire, minor injuries to crew, remaining with car, over"

OK, I could go on and on forever about comms and comms procedures, but before I start quoting classified tactical radio comms procedures and going on about tropospheric ducting of signals, we'd better call it a day.

Once you have your kit installed and your voice procedure down, that's not the end. The smart tactical racers and their crews will develop their own comms plan which may include things like:

• How they plan to transmit sitreps / position reports
• Using a relay station
• Lost-comms procedures (what to do when you can't reach each other  - switching to different channels, using a relay, etc.)
• Scanning and multi- radio ops  (monitoring more than one net simultaneously)
• Sniping intel on other teams and race stats from other nets and transmitting it to the car
• etc.

Perhaps that might be the subject for another article one day!