The Invisible World of Radio Signals

Thousands of signals fill the air around you right now. Police dispatches, weather satellites, aircraft communications, amateur radio operators, and more. This interactive encyclopedia helps you discover what's broadcasting and how to listen.

50+ Frequency Bands
25 MHz to 1.7 GHz
$25 to Start Listening

Interactive Spectrum Explorer

Click any band below to learn who uses it, what it sounds like, and whether you can listen. Use filters to find signals matching your equipment.

AM Broadcast 530-1700 kHz
FM Broadcast 88-108 MHz
HF Amateur 1.8-30 MHz
Air Band 108-137 MHz
2m Amateur 144-148 MHz
VHF Public Safety 150-174 MHz
Marine VHF 156-162 MHz
NOAA Weather 162-163 MHz
70cm Amateur 420-450 MHz
UHF Public Safety 450-470 MHz
Weather Satellites 137-138 MHz
ADS-B Aircraft 1090 MHz
GPS L1 1575 MHz

Click a frequency band above to see details

Equipment Guide

You don't need expensive gear to start exploring radio signals. Here's what works at different budget levels.

$10-30

Getting Started

  • RTL-SDR Blog V3 dongle
  • Receives 24 MHz to 1.76 GHz
  • Free software (SDR#, GQRX)
  • Basic included antenna

Best for: FM radio, air traffic, weather satellites, ADS-B aircraft tracking, amateur radio, public safety (if not encrypted).

$50-150

Serious Listening

  • RTL-SDR Blog V4 or Airspy Mini
  • Better sensitivity and filtering
  • External antennas for weak signals
  • Upgraded cables and connectors

Best for: Weak signal reception, satellite imagery, long-distance HF with upconverter, cleaner reception in noisy environments.

$200-500

Advanced Setup

  • Airspy HF+ Discovery or SDRplay
  • Wideband coverage (kHz to GHz)
  • Professional-grade filtering
  • Multiple antenna inputs

Best for: DXing (long-distance reception), contesting, satellite work, weak signal digital modes, serious amateur radio.

$500+

Professional Grade

  • Icom IC-R8600 or similar
  • Standalone receiver (no computer needed)
  • Superior build quality
  • Advanced scanning features

Best for: Dedicated monitoring stations, emergency communications, professional applications, users who want a traditional radio experience.

Antenna Tips

The antenna matters as much as the receiver. For VHF/UHF (100 MHz and up), a simple dipole or discone antenna works well. For HF (below 30 MHz), you need a longer wire antenna. For weather satellites, a QFH or turnstile antenna gives best results. Keep antennas away from computers and power supplies to reduce noise.

About This Encyclopedia

The radio spectrum is invisible, but it's packed with activity. Every second, thousands of signals pass through your body. Police officers talking to dispatches. Pilots coordinating with air traffic control. Weather satellites beaming down images of storms. Amateur radio operators chatting across continents. Ships navigating coastal waters.

Until recently, listening to these signals required expensive equipment. Now, a $25 software-defined radio dongle and a free program let you explore this hidden world from your laptop. But knowing what to listen to and where to find it can be overwhelming. That's why this encyclopedia exists.

We built this reference to bridge the gap between curiosity and understanding. Whether you're a complete beginner who just discovered SDR or an experienced operator looking for a quick frequency reference, you'll find what you need here. Each band includes real frequency ranges, explains who uses them, describes what they sound like, and tells you what equipment you need.

The frequencies listed focus on common allocations in the United States. Other countries may assign different services to the same frequencies. Always verify local regulations before transmitting. Receiving is almost always legal, but transmitting requires proper licensing.

Start with the interactive spectrum chart above. Click around. Discover something new. The airwaves are waiting.

Common Beginner Mistakes

  • Expecting too much from the stock antenna. The little antenna included with RTL-SDR kits works, but an external antenna dramatically improves reception.
  • Trying to listen to digital signals with analog equipment. Many public safety systems use digital modulation (P25, DMR). You need a digital-capable receiver or SDR with decoding software.
  • Confusing frequency with channel. Radios display channel numbers, but you need the actual frequency to program a scanner or SDR.
  • Ignoring modulation type. A signal on 146.520 MHz could be FM, AM, or SSB. Using the wrong demodulation setting gives you silence or garbled audio.
  • Not checking if signals are encrypted. Some public safety agencies encrypt their communications. No equipment can decode these legally.