FRS (Family Radio Service) and GMRS (General Mobile Radio Service) are UHF services operating on 22 shared channels between 462–467 MHz. FRS radios are license-free handheld units limited to 2 W — ideal for hiking, camping, family outings, and short-range team coordination up to about 1–2 miles in open terrain (less through buildings or dense foliage). GMRS allows up to 50 W and repeater use, extending range to several miles or more, making it popular for off-roading convoys, neighborhood emergency preparedness, and rural properties. Radios are inexpensive ($25–$150), require no exam, and work instantly out of the box.

Marine VHF operates on 156–174 MHz and is the universal communication standard for vessels on coastal waters, lakes, and rivers. Handheld radios transmit at 5 W (range ~5 miles); fixed-mount units reach 25 W with a range of 20+ miles to shore stations and other vessels. Channel 16 is the international distress and hailing frequency monitored 24/7 by the U.S. Coast Guard and all commercial vessels — every marine radio must monitor it. Marine VHF also carries NOAA weather broadcasts (WX channels), Digital Selective Calling (DSC) for automated distress alerts, and port-operations traffic. It is the safest and most reliable way to call for help on the water.

CB (Citizens Band) Radio operates on 40 channels around 27 MHz (HF) and has been a staple of truckers, off-roaders, and rural communities since the 1970s. At 4 W AM / 12 W SSB, typical range is 1–5 miles for AM; SSB can reach 10–20 miles or farther under good conditions. Because CB uses HF frequencies, signals can bounce off the ionosphere and occasionally propagate hundreds of miles — a phenomenon called "skip." Channel 9 is the national emergency channel; Channel 19 is the highway trucker channel used across North America. No license, no registration, no exam — just key up and talk. Radios range from $30 handhelds to full mobile units.

Civil aviation uses AM voice on VHF frequencies between 118–137 MHz — AM was kept (instead of FM) specifically because two overlapping AM signals degrade into readable noise rather than fully blocking each other like FM does, which matters when multiple aircraft key up near-simultaneously. 121.500 MHz is the international VHF Guard emergency frequency monitored worldwide. 122.700–123.075 MHz covers Unicom, the uncontrolled-airport advisory frequency pilots use to self-announce position and intentions. The 123.1–123.575 MHz range is largely Flight Test itinerant use by aircraft manufacturers and modification shops. This reference is receive-focused — actual ATC tower/approach/center frequencies are airport-specific and not included here.

Civil Air Patrol channels use P25 Phase 1/2 digital voice with Network Access Codes (NAC), not analog AM/FM — you'll need a P25-capable SDR mode to decode them.