Your car radio, your cell phone, and your Wi-Fi all do the same basic thing: they send and catch invisible radio waves. If you know how to tune your car radio to a station, you already understand most of wireless. These six pictures start with waves on a lake, then show the radios in your home, call signs, and Wi-Fi.

Radio Waves Are Like Water Waves
Radio Waves Are Like Water WavesA lake with waves rolling past a buoy. Three peaks pass the buoy in one second, which is 3 hertz. An arrow shows the wavelength, the distance between peaks. A card defines 1 hertz as 1 peak per second, a kilohertz as a thousand, a megahertz as a million, and a gigahertz as a billion. Two strips compare low frequency, with few peaks and long waves, to high frequency, with many peaks and short waves.RADIO WAVES ARE LIKE WATER WAVESBuoyPeak 1Peak 2Peak 3One second of waves rolling past the buoy3 peaks pass each second = 3 hertz (3 Hz)WavelengthWaves move this way →Counting wave peaks1 hertz (Hz)1 peak every second1 kilohertz (kHz)1,000 peaks a second (a thousand)1 megahertz (MHz)1,000,000 a second (a million)1 gigahertz (GHz)1,000,000,000 a second (a billion)Low frequency: few peaks, long wavesHigh frequency: many peaks, short waves123456
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  1. 1Like ripples on a lake. Drop a stone in a lake and ripples spread out in every direction. A radio antenna sends out radio waves the same way, except radio waves are invisible and travel at the speed of light.
  2. 2Wave peaks. Every wave has high points, called peaks. Watch the buoy bob up and down and count how many peaks roll past it each second. That count is the wave's frequency.
  3. 3Hertz. One peak per second is called 1 hertz (Hz), named for Heinrich Hertz, the German scientist who proved radio waves exist in the late 1880s. In this picture, 3 peaks pass the buoy every second, so the frequency is 3 hertz.
  4. 4Kilo, mega, and giga. Radio waves wiggle much faster than lake waves, so we use bigger units. Kilo means a thousand, mega means a million, and giga means a billion. KWNA at 92.7 FM sends 92.7 million wave peaks every second. 2.4 GHz Wi-Fi sends 2.4 billion.
  5. 5Wavelength. Wavelength is the distance from one peak to the next. More peaks per second means the peaks are packed closer together. An AM radio wave is hundreds of meters long, an FM wave about 3 meters, and a 2.4 GHz Wi-Fi wave only about 12 centimeters, or 5 inches.
  6. 6Where the comparison stops. Water waves need water, but radio waves do not need anything to travel through. They cross empty space, which is how signals from GPS satellites reach your phone.
Every Wireless Gadget Is a Radio
Every Wireless Gadget Is a RadioA rainbow ruler of radio frequencies from low to high, marking AM radio near 1 MHz, FM radio from 88 to 108 MHz, cell phones from 600 MHz to 4 GHz, Wi-Fi and Bluetooth at 2.4 GHz, Wi-Fi at 5 and 6 GHz, and 5G high band at 24 GHz and up.EVERY WIRELESS GADGET IS A RADIOLow frequency: few peaks, long wavesHigh frequency: many peaks, short wavesAM radioaround 1 MHzFM radio88 to 108 MHzCell phones600 MHz to 4 GHzWi-Fi and Bluetooth2.4 GHzWi-Fi5 and 6 GHz5G high band24 GHz and up123456
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  1. 1It is all radio. Car radios, cell phones, Wi-Fi, Bluetooth headphones, and garage door openers all send invisible radio waves through the air. They travel at the speed of light.
  2. 2Frequency. Remember the lake: frequency is how many wave peaks pass each second, counted in hertz. Low frequencies, on the left, have few peaks and long waves. High frequencies, on the right, have many peaks and short waves.
  3. 3Your car radio. When you tune your car radio to 92.7 FM in Winnemucca, you are choosing KWNA, the station that broadcasts at 92.7 megahertz. AM stations sit much lower, around one megahertz, which is one reason AM can be heard so far away.
  4. 4Your cell phone. Cell phones use frequencies from about 600 MHz up to about 4 GHz. Phone companies hold licenses for blocks of these frequencies, just like a radio station holds a license for its spot on the dial.
  5. 5Wi-Fi and Bluetooth. Wi-Fi and Bluetooth use frequencies around 2.4 GHz, and Wi-Fi also uses 5 GHz and 6 GHz. These are shared, unlicensed bands, so many gadgets use them at once.
  6. 6The trade-off. Lower frequencies travel farther and pass through walls and hills. Higher frequencies carry more data but fade faster. Every wireless network balances distance against speed.
Frequency Ranges at Home
Frequency Ranges at HomeA comparison chart of everyday radios on a stretched scale from 1 MHz to 10 GHz: AM radio 540 to 1700 kHz, FM radio 88 to 108 MHz, GPS at 1575.42 MHz, Bluetooth and microwave ovens in the 2.4 GHz band, and Wi-Fi at 2.4, 5, and 6 GHz.FREQUENCY RANGES AT HOME1 MHz10 MHz100 MHz1 GHz10 GHzLower frequency ← → Higher frequencyRangeAM radio540 to 1700 kHzFM radio88 to 108 MHzGPS (maps)1575.42 MHzBluetooth2.4 to 2.4835 GHzMicrowave ovenSame 2.4 GHz bandWi-Fi 2.4 GHz2.4 to 2.4835 GHzWi-Fi 5 GHz5.15 to 5.85 GHzWi-Fi 6 GHz5.925 to 7.125 GHz123456
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  1. 1Car radio. AM radio sits way down near 1 megahertz (MHz). FM radio runs from 88 to 108 MHz, which is why your car radio dial reads 88 at one end and 108 at the other. Each FM station gets a slice 0.2 MHz wide.
  2. 2GPS. The Global Positioning System (GPS) that powers your map app listens for satellites broadcasting at 1575.42 MHz. Your phone only receives this signal; it never transmits on it.
  3. 3Bluetooth and the microwave. Bluetooth headphones, microwave ovens, and many other gadgets all share the same unlicensed 2.4 gigahertz (GHz) band. That is why a running microwave can slow down nearby 2.4 GHz Wi-Fi.
  4. 4Wi-Fi 2.4 GHz. The 2.4 GHz Wi-Fi band runs from 2.4 to 2.4835 GHz, 83.5 MHz in all. It reaches farthest through walls, but it is shared by the most devices.
  5. 5Wi-Fi 5 and 6 GHz. Wi-Fi also uses 5 GHz (about 5.15 to 5.85 GHz) and, since 2020, 6 GHz (5.925 to 7.125 GHz). The 6 GHz band alone is 1,200 MHz wide, so it has room for many more fast channels.
  6. 6Why the bars look so thin. This chart uses a stretched scale so AM radio and Wi-Fi fit on one picture: each grid line is 10 times the one before it. On a normal ruler, the 2.4 GHz Wi-Fi band (83.5 MHz) would be about four times wider than the whole FM dial (20 MHz).
Tuning In: Frequency and Call Sign
Tuning In: Frequency and Call SignA car radio tuned to 92.7 FM, a broadcast tower with a sign reading KWNA-FM 92.7 FM, and a call sign card for KWNA-FM, All American Country, licensed to Elko Broadcasting Company on 92.7 MHz in Winnemucca, Nevada. A second card shows Red Mountain Networks' 2.5 GHz Educational Broadband Service call sign, WRWK316, with Numu Communications as licensed operator.TUNING IN: FREQUENCY AND CALL SIGN88929610010410892.7 FMYour car radioKWNA-FM92.7 FMCALL SIGN: KWNA-FMStationAll American CountryLicenseeElko Broadcasting Co.Frequency92.7 MHzCityWinnemucca, NevadaRed Mountain NetworksWRWK316 · 2.5 GHz EBSNumu Communications, licensed operatorTune to one stationEach station, one frequencyThe FCC keeps the list12345
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  1. 1Tuning. Turning the dial picks one frequency, such as 92.7 FM in Winnemucca, Nevada. Your radio listens only to that frequency and ignores every other station in the air around you.
  2. 2The station. Each radio station sends its signal on one assigned frequency from a tall tower. If two nearby stations used the same frequency, you would hear both garbled together, which is called interference.
  3. 3The call sign. Every station has a call sign, like a name tag. 92.7 FM in Winnemucca is KWNA-FM. In the United States, call signs start with K west of the Mississippi River and W east of it, with a few older exceptions, and the -FM on the end tells you it is an FM station. Stations must say their call sign at the top of every hour.
  4. 4The call sign is the license. The Federal Communications Commission (FCC), the U.S. agency in charge of the airwaves, gives each station a license, and the call sign is that license's name. Look up KWNA-FM and you find its owner, Elko Broadcasting Company, its frequency, 92.7 MHz, its city, Winnemucca, and how much power it may use, so stations do not step on each other.
  5. 5Wireless networks have call signs too. Cell phone companies, internet providers, and tribes hold FCC licenses for blocks of frequencies in a specific area, and each license has its own call sign. Red Mountain Networks in Fort McDermitt uses call sign WRWK316 in the 2.5 GHz Educational Broadband Service (EBS), with Numu Communications as its licensed operator. In 2020, the FCC opened a Rural Tribal Priority Window so tribes could get 2.5 GHz licenses over their own lands.
Licensed Lanes and the Open Park
Licensed Lanes and the Open ParkOn the left, a highway with reserved lanes for KWNA 92.7 FM, a cell company, and tribal 2.5 GHz, marked License required. On the right, an open park shared by Wi-Fi, Bluetooth headphones, a microwave oven, a garage opener, and a baby monitor.LICENSED LANES AND THE OPEN PARKKWNA 92.7 FMCell companyTribal 2.5 GHzRESERVED LANESLicense requiredOPEN PARKShared by everyoneWi-FiBluetoothMicrowaveGarage openerBaby monitorLicensedUnlicensed12345
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  1. 1Licensed. Some frequencies are like reserved highway lanes. Only the license holder may use that lane in that area: radio and TV stations, cell phone companies, and tribes with 2.5 GHz licenses.
  2. 2Protection. Because the lane is reserved, nobody else is supposed to use it. If someone causes interference, the FCC can step in. That protection is why licensed networks can cover wide areas reliably.
  3. 3Unlicensed. Other frequencies are like an open public park. Anyone may use them without a license: Wi-Fi, Bluetooth, cordless phones, baby monitors, and garage door openers all share this space.
  4. 4Rules still apply. Unlicensed does not mean no rules. Devices must stay at low power and be approved by the FCC. Look for the "FCC ID" label on the bottom of your router or phone.
  5. 5It can get crowded. Because everyone shares the park, it can get busy. Your neighbor's Wi-Fi, Bluetooth headphones, and even a running microwave oven can slow your 2.4 GHz Wi-Fi.
Wi-Fi's Three Bands: 2.4, 5, and 6 GHz
Wi-Fi's Three Bands: 2.4, 5, and 6 GHzA home floor plan with a router in the middle and three circles: a large yellow 2.4 GHz circle that reaches farthest, a medium blue 5 GHz circle, and a small green 6 GHz circle. A microwave and a neighbor's router sit near the edge, and a list shows Wi-Fi channels.WI-FI'S THREE BANDS2.4 GHz: reaches farthest5 GHz: faster6 GHz: fastest, shortestMicrowaveNeighbor's Wi-FiChannelsCh 1Ch 6Ch 11Ch 36Ch 149Ch 6EYour router is a tiny radio station12345
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  1. 12.4 GHz. The 2.4 GHz band reaches the farthest and goes through walls best. But it is the most crowded: Bluetooth, microwave ovens, baby monitors, and your neighbors' Wi-Fi all share it.
  2. 25 GHz. The 5 GHz band is faster and has more channels, so it is less crowded. Its signal does not reach as far or pass through walls as well.
  3. 36 GHz. The FCC opened the 6 GHz band to Wi-Fi in 2020, adding 1,200 MHz of new room. It is the fastest and least crowded, but it has the shortest reach and needs a newer device labeled Wi-Fi 6E or Wi-Fi 7.
  4. 4Channels. Each band is split into channels, like stations on a radio dial. Your router picks a channel to broadcast on. If a neighbor's router uses the same channel, the two take turns, which slows both down.
  5. 52.4 is not 2.5. The numbers look alike, but 2.4 GHz Wi-Fi is unlicensed and short-range, made for inside a home. The 2.5 GHz band next to it is licensed, like a radio station, and is used for wide-area wireless networks, including the tribal licenses.

Remember

Frequency is wave peaks per second, counted in hertz

A call sign is the name of a station's FCC license

Wi-Fi shares open bands: 2.4, 5, and 6 GHz

Try it

1. If 5 wave peaks pass the buoy every second, what is the frequency?

2. Your car radio, cell phone, and Wi-Fi all use what?

3. What does a call sign tell you?

4. Which Wi-Fi band can a running microwave oven slow down?

Learn more

References

  1. Federal Communications Commission. (2018, October 2). Unlicensed use of the 6 GHz band [Fact sheet]. https://docs.fcc.gov/public/attachments/DOC-354364A1.pdf
  2. Federal Communications Commission. (2020). FCC opens 6 GHz band to Wi-Fi and other unlicensed uses. https://www.fcc.gov/document/fcc-opens-6-ghz-band-wi-fi-and-other-unlicensed-uses
  3. Federal Communications Commission. (n.d.-a). KWNA-FM public inspection file. https://publicfiles.fcc.gov/fm-profile/KWNA-FM
  4. Federal Communications Commission. (n.d.-b). Universal Licensing System: License search. https://wireless2.fcc.gov/UlsApp/UlsSearch/searchLicense.jsp
  5. Federal Communications Commission. (n.d.-c). Why do FM frequencies end in an odd decimal? https://www.fcc.gov/media/radio/fm-frequencies-end-odd-decimal
  6. Mishkind, B. (n.d.). Broadcast station hourly identifications: When and how. The Broadcasters' Desktop Resource. https://www.thebdr.net/broadcast-station-hourly-identifications-when-and-how/
  7. National Coordination Office for Space-Based Positioning, Navigation, and Timing. (n.d.). New civil signals. GPS.gov. https://archive.gps.gov/systems/gps/modernization/civilsignals/
  8. National Telecommunications and Information Administration. (2025). United States frequency allocation chart. https://www.ntia.gov/page/united-states-frequency-allocation-chart
  9. Telecommunications Law Professionals. (2020, October 26). FCC grants 2.5 GHz licenses in Rural Tribal Priority Window. https://www.tlp.law/2020/10/26/fcc-grants-2-5-ghz-licenses-in-rural-tribal-priority-window/
  10. TV Obscurities. (2009, November). Q & A: The mystery of K and W call letters. https://www.tvobscurities.com/2009/11/q-and-a-the-mystery-of-k-and-w-call-letters/

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