Learn / Guide 2
Spectrum map: who lives in each band
From long waves to 1090 MHz: what to hear in each slice of the spectrum and at what times it is worth looking.
beginner 6 min read
How to read an address on the radio
Every signal has a frequency, measured in hertz. Everyday use includes kilohertz (kHz, thousand) and megahertz (MHz, one million).
Radio amateurs and DXers also talk in meters. It is the wavelength, and the math is simple: 300 divided by the frequency in MHz. Seven megahertz gives about 43 meters, and the band earned the rounded name of 40 meters.
The major acronyms divide the spectrum into decades:
- LF (long waves): 30 to 300 kHz
- MF (medium waves): 300 kHz to 3 MHz
- HF (short waves): 3 to 30 MHz
- VHF: 30 to 300 MHz
- UHF: 300 MHz to 3 GHz
The most important boundary is at 30 MHz. Below it, the signal can bounce back from the ionosphere and land on another continent. Above it, almost everything travels in line of sight: dozens of kilometers between two antennas on the ground, hundreds when the transmitter is flying.
Who lives where
| Band | Frequency | What is heard | Best time |
|---|---|---|---|
| Longwave | 30 to 300 kHz | navigation radio beacons, time signals, the few remaining stations in Europe | night |
| Medium wave | 530 to 1,700 kHz | AM stations | local by day, distant at night |
| 160 m (amateur radio) | 1.8 to 2.0 MHz | telegraphy and LSB voice | night, better in winter |
| Tropical bands (120, 90, and 60 m) | 2.3 to 5.06 MHz | regional stations of tropical countries | night |
| 80 m (amateur radio) | 3.5 to 4.0 MHz | regional chat in LSB, telegraphy | night |
| 49 m (broadcasting) | 5.9 to 6.2 MHz | international stations | night |
| 40 m (amateur radio) | 7.0 to 7.3 MHz | voice in LSB, telegraphy, FT8 on 7.074 | regional by day, distant at night |
| 41 m and 31 m (broadcasting) | 7.2 to 7.45 and 9.4 to 9.9 MHz | international stations | late afternoon and night |
| 30 m (amateur radio) | 10.1 to 10.15 MHz | telegraphy and digital modes only | almost all day |
| 25 m and 19 m (broadcasting) | 11.6 to 12.1 and 15.1 to 15.8 MHz | international stations | day and early evening |
| 20 m (amateur radio) | 14.0 to 14.35 MHz | long-distance contacts in USB, FT8 on 14.074 | day, with peaks at dawn and dusk |
| 17, 15 and 12 m (amateur radio) | 18.068 to 18.168; 21.0 to 21.45; 24.89 to 24.99 MHz | long distance | day, better with active Sun |
| 11 m (citizens band, CB) | channels from 26.965 to 27.855 MHz | AM and SSB on channels | day, with active Sun |
| 10 m (amateur radio) | 28.0 to 29.7 MHz | long distance, FM above 29 MHz | day, with active Sun; summer |
| 6 m (amateur radio) | 50 to 54 MHz | sudden openings | summer, late afternoon |
| FM | 88 to 108 MHz (in Brazil also 76 to 88, the extended FM) | local stations | always |
| Air band | 118 to 137 MHz | pilots, towers, and airport information, in AM | hours of movement |
| 2 m (amateur radio) | 144 to 148 MHz | FM repeaters, APRS, Space Station on 145.800 and 145.825 | always, ISS only during pass |
| 70 cm (amateur radio) | 430 to 440 MHz | FM and DMR repeaters, satellites | always |
| ADS-B | 1,090 MHz | aircraft position and altitude | always |
The amateur radio band limits above are for ITU Region 2, which covers the Americas. Brazilian limits, including segments for each class, are in Anatel Act 926/2024, and the guide How to become an amateur radio operator explains the classes.
The rule of day and night
If you only remember one thing, remember this: low frequencies at night, high frequencies during the day. The dividing line is near 10 MHz.
During the day, a low layer of the ionosphere absorbs anything below about 7 MHz, and medium waves only reach the local region. The 20 to 10 meter bands, on the other hand, need the Sun to work. When night falls, the game flips: 49, 41 and 40 meters fill up with distant signals and the high bands fade away.
Broadcasting and amateur radio are neighbors, not the same thing
Broadcasting band is where commercial stations are, with public programming, in AM and 5 kHz channels. Amateur radio band is where licensed operators talk to each other, in SSB, telegraphy and digital modes.
The two touch each other, and at one point they mix. In the Americas, the 7,200 to 7,300 kHz segment is for amateur radio. In Europe, Africa and Asia, the same segment is for broadcasting. At night, when 40 meters opens up for long distance, strong stations from other continents appear on top of local conversations.
What lies between the bands
The rest of the shortwave spectrum is not empty. Between one band and another live the services that people call utilities:
- aircraft on oceanic routes talking to control in USB;
- time signal stations on 2,500, 5,000, 10,000, 15,000 and 20,000 kHz;
- weather charts via facsimile;
- military and diplomatic communications, almost always encrypted.
What fits in each remote receiver
A KiwiSDR covers from 10 kHz to 30 MHz all at once: every row in the table up to the 10 meter band.
From 30 MHz upwards the signal is local, and what matters is where the receiver is. For the airband, a 2-meter repeater or the Space Station, look for an OpenWebRX that covers VHF in the region of interest, or build your own receiver.