Field Day is an annual amateur radio exercise, sponsored by the ARRL and held in North America, in which clubs and groups set up temporary stations outdoors, usually on emergency-style power, and try to make as many contacts as they can in a fixed period. It is half contest, half practice for the day normal communications and power are not available. It is also a well-known public open house for the hobby.
What happens
Illustrative layout. Real sites follow the terrain, the club and the program's current rules.
Typically a club chooses a site, builds several stations on different bands and modes at once, powers them from generators, batteries or solar, and keeps a shared log. Operators take shifts. The exercise tests whether you can get a working station on the air quickly, from nothing, outdoors.
Because the emphasis is on emergency readiness, alternative power and improvised antennas are encouraged, and the sponsor has offered bonus points for things like a public information table or media coverage. The details change every year; check the current rules for the categories and bonuses.
A logging plan. Most groups use shared or networked logging software so that two stations never work the same one twice in the same band and mode. See Logging and contest software.
A site you have permission to use, with room for antennas, safe spacing and parking.
People. Setup, antenna raising, operating, logging and cooking all need volunteers.
Making it work
Plan the stations apart. Two transmitters near each other can overload each other's receivers, so stations on different bands are spaced and filtered. See Receiver overload and intermodulation.
Put power in its own place, away from tents and from people, with fuel safely stored. Generator exhaust contains carbon monoxide, so never run one inside or next to an enclosed space. See Battery and fire safety.
Raise antennas carefully. Look up for power lines, use enough people, and never leave a mast or wire where a person or a vehicle can hit it. See Tower and climbing safety.
Keep the public in mind. Visitors can see how a station works, try a contact, and meet a club. A friendly greeter makes a big difference. See Clubs, Elmers and community.
Use it as a rehearsal. Practice what you would do in a real emergency: setup time, backup power, message handling. See Go kits and emergency power.