Communicating With Radio Waves

by Meli Lewis

In the winter of 2007, a series of storms hit the Pacific Northwest coast over several days, with winds over 100 mph and record flooding even in inland cities.¹ Power, landlines, and cell phone towers were unavailable on the coast of Oregon for days after. The state was formally unable to declare an emergency and provide assistance without communication from the affected areas. Even if resources could be deployed, it was impossible to discern what was needed where.²

Communication ultimately came thanks to a network that integrates radio and internet technology.³ The internet is made possible through a combination of radio technology (think mobile phones and wireless connections) and comprehensive physical infrastructure (poor Ted Stevens,⁴ it really is a series of tubes⁵). But the radio system that made communication possible was so modest it predated the fallen telecommunication systems, could run from batteries, and be made from spare parts.

Amateur radio, so called because it is legally designated for people who don’t use these communications for profit, arose around a century ago. Though it has evolved to use smaller and more efficient components, the principles underlying its operation remain simple. At a high level, a radio needs only a transmitter system by which a signal (e.g. sound) is turned into electricity; a receiver system by which that a signal is converted to a usable form (e.g. sound again); and an antenna for converting between electricity and radio waves.

Making Waves

When we talk about radio waves, we’re talking about just one of many categories of electromagnetic radiation, including visible light and x-rays. Radio waves are relatively long and can range from about the size of a flea (1 mm) to about five times the length of Manhattan Island (100 km).

On the same continuum, the waves that underlie visible light are much shorter.⁶ The color of an object is determined by the length of the waves of energy leaving its surface: for example, the waves that make an apple look red are about 30% longer than the waves that make an apple look green.⁷

Like an antenna intercepts energy from radio waves and converts it to an electrical signal, the eye intercepts energy from light waves and converts them to electrical signals.⁸

If you’ve ever used sunglasses that appear to make colors warmer, you may have been⁹ experiencing the messiness of the electromagnetic spectrum. In trying to filter out damaging waves in the form of ultraviolet light, the glass is also filtering similarly short¹⁰ waves of violet and blue light! Similarly, when you select a radio station, you’re filtering out other waves on the basis of a property linked to wavelength: frequency.

During a minute that I’m sitting at home listening to KOPB 91.5 FM and my neighbor is listening to KBOO 95.5 FM, the speed at which our respective radio station’s waves arrive is about the same: 299,792,458 meters per second,¹¹ known more affectionately as the speed of light. Because the relationship between wavelength and frequency is inverse, and I already know radio waves travel at about the speed of light, I can determine without any calculation¹² that his radio waves are shorter.

Taken together, speed and the linked properties of wavelength and frequency are sufficient to describe radio waves as a general phenomenon, but to talk about radio technology, we have to cover the other two characteristics it modulates: amplitude and phase.

Radio Technology

Amplitude is the easier of the traits to describe because it is more simply (albeit imperfectly) described as the height of a wave. When a wave is not modulated—that is, when its amplitude and frequency are constant—it’s called a continuous wave. What type of modulation is best depends on the kind of signal you’re trying to send, as it’s possible to transmit not just sound as we commonly experience with car radio, but also text and images.

Modulation by abruptly stopping and starting these continuous waves is the simplest way to convey information in a transmission, and is the mechanism for Morse code.¹³ However, to convey something as richly varied as a song or human voice, it’s not enough to simply turn a signal on and off. This is the role of amplitude modulation (AM) radio: to vary a characteristic of the wave in a more complex way. As the amplitude of the sound changes, the amplitude of the radio wave changes identically. While this is indeed the AM you’ll recognize from broadcast radio, this method is also among the options for amateur operators.

However, AM radio has a few drawbacks. Put most simply, radio waves with amplitude modulation have some amount of redundancy that makes them easier to demodulate or transmit back into an understandable signal, at the cost of requiring more power than if they had less redundancy. Additionally, incidental forces like electricity from a storm can affect the amplitude changes in unintended ways to make a transmission less clear—it often manifests as static. Frequency modulation (FM) is a more recent technique for embedding information in radio waves.

Like with AM, complex sounds like music and voice are mapped onto the wave, but their impact is on frequency alone. AM and FM serve as complements, in that FM provides greater fidelity of sound, but AM can travel farther. Indeed, one of the most popular types of AM is called single-sideband modulation (SSB), which drops AM redundancy, thereby extending how far a particular amount of power can go, but also necessitating more specialized equipment.

AM and FM as described here are much simplified. They are a subset of the methods available to transmit a signal like speech over radio waves, but should be enough to get you oriented to amateur radio equipment and licensing.

Equipment

Now that we’ve gone over the components of radio waves, we can revisit the equipment acting on them: the transmitter, which translates input like voice or music into electricity; the antenna, which takes such a current and converts it to radio waves; and the receiver, which converts that electricity back into a signal. Where a car uses a one-way radio system (stations transmit to you) and needs just an antenna and receiver, amateur radio uses a two-way system¹⁴, and so combines all of the above into a category of device called a transceiver. A feed line is the cable connecting the antenna to the transmitter and/or receiver.¹⁵

Radio equipment can be stationary or mobile, and when mobile can also be handheld (e.g. walkie-talkie). Two-way radios, like one-way, also rely on selecting channels, but instead to allow many people at once to reach each other simultaneously, rather than to receive the same signal from a broadcast station.

How powerful radio equipment is—that is, how much energy it can recruit for transmitting radio waves—circumscribes what channels it can use. Less powerful radios are available for anyone to use,¹⁶ and cannot transmit as far. With great transmitting power comes great responsibility—to the government.¹⁷

Licensing

Amateur (also called ham) radio operators exist all over the world¹⁸ and are regulated by agencies both within and among their respective countries, but this article will focus on licensing in the United States.

The Federal Communications Commission (FCC), founded in 1934, today regulates a great variety of communication technologies, including the internet. It regulates what subsets of the radio spectrum are used for which applications, e.g. broadcasting and amateur radio. This means amateur radio operators aren’t legally allowed to take over your favorite broadcast radio station, and people seeking to profit aren’t legally allowed to hang out on your buddy’s amateur channel.

Among the ways the FCC regulates radio behavior is by licensing: the low-powered radios called FRS earlier do not require a license, but some radios that combine it with slightly greater power, GMRS (between 1 and 5 watts) require a fee and registration. More rigorous still is membership in the International Amateur Radio Union, whose power allowances vary according to its constituent countries’ own rules. In the US the greatest transmitting power is 1.5 kW,¹⁹ though it mandates each operator use the minimum amount of power needed to successfully transmit.

Though the categories and criteria have evolved since licensing began, today the window of power afforded an operator contains three tiers. They are, in order of advancement: technician, general, and amateur extra. Both because I have only passed the technician exam and for the sake of brevity, this section will focus on its content.

Each license requires passing an in-person exam proctored by licensed radio operators. You can find locations and dates of upcoming exams in your area, and many allow you simply to walk in on the day you’re ready. Though the subject areas overlap among the tests, their question pools are entirely distinct.²⁰

License	Question pool size	Minimum number of correct answers required to pass
technician	300	26/35
general	500	26/35
amateur extra	713	37/50

The subject areas of the technician exam include many topics this article has already touched upon: radio and signals fundamentals; electricity, components, and circuits; propagation, antennas, and feed lines; amateur radio equipment; communicating with other hams; licensing regulations; operating regulations; and safety.

The Test

My own test was in the community center of a church, with a handful of operators acting as proctors and about a dozen other people either receiving their first license or upgrading. Because the exam is multiple choice and grading is by hand using a physical grading template, it’ll be a good idea to use a pencil so you can erase. It’s okay to sit near other people; there are several versions such that it won’t be possible to simply copy another person’s answering pattern. You can bring a calculator if need be (for things like converting between frequency and wavelength), but if it has a memory function the proctor may clear memory and/or not allow you to use it.

You’ll pay $15 on-site and, if you pass your first exam, you will be provided the chance to take the exam for higher licenses at no extra charge! After passing the technician exam I attempted the general without having studied and found my technician prep was sufficient to get 17/35 (where I would have needed 26/35 to pass). However, general exam questions dive deeper into theory, and my hunch is that they’ll make more sense after I have more practice actually using and experimenting with a radio of my own.

The two most important aspects of taking the test that I wish I’d known before going in are 1) that I should get an FCC Registration Number (FRN) to provide for when I earn the exam, and 2) that the address I provide will be public, and as of this writing, permanently so.²¹ It’s good to have an FRN because it is a secure alternative to writing out your social security number, especially on a document that has other identifying information. The address you provide for your license documentation simply has to be a mailing address through which you can be reached, which is certainly ideal if it’s going to be publicly available.

Ham Social

I earned the license to serve as an emergency responder, but since studying for it I have loved meeting other operators! Anyone with a license has a chance to participate in contests to contact as many other people as possible or to make contact over as great a distance as possible; we also have an opportunity to volunteer for emergency response and public service. I know that having the capacity to communicate when other systems might be down is not only personally reassuring, but it’s an honor to consider doing this for other people.

I’ll part with a section of the FCC description, as a fundamental purpose of amateur radio: “continuation and extension of the amateur’s unique ability to enhance international goodwill.”²² That this would be foundational to a relatively old communication technology sets a lovely context for everything that has followed.

Resources

I used two resources for studying: hamstudy.org and the ARRL Ham Radio License Manual, the latter of which I also used as a resource for writing this article. Additionally, you can write to the people behind hamstudy.org to request use of their API, through which you can access all of the exam content in JSON!

If you’re interested in becoming an operator for emergencies, you can join the Amateur Radio Emergency Service and/or Radio Amateur Civil Emergency Service. For more on the differences between these, you can visit http://www.arrl.org/ares-races-faq.

Notes

Meli Lewis is a Python programmer, open source contributor, and disaster response volunteer. Her day job is as the data editor for The Oregonian.