A UHF scanner is a handheld, mountable, or desktop device that receives a wide range of UHF transmission frequencies. These receivers often permit easy push-button access and automatic tuning across the band, allowing users to listen in and keep abreast of local events. Units can differ by size, scanning methods, and internal technology.
The ultra high frequency (UHF) band is a portion of the electromagnetic (EM) spectrum typically reserved for radio communication of public agencies. These can include ambulance, police, and fire transmissions. It is also used by air and amateur radio services.
Scanners come in three basic configurations: handheld, mobile, and desktop designs. Handheld units resemble walkie-talkies, which are portable for field use. Mobile units mount on dashboards or with detachable control heads and can be connected to one or more vehicle-mounted antennas. Desktop varieties can be hooked to larger base-station antennas to increase range. A UHF scanner can pick up radio transmissions from mobile and base stations, repeaters, control stations, and more.
Some types of UHF scanner can serve either as as base station or mobile unit. These typically possess an external antenna. Such devices not only scan preprogrammable channels, but are able to detect nearby transmissions and automatically zero in on their frequencies. This functionality affords access to a broad variety of UHF transmissions, from 300 megahertz (MHz) to 3 gigahertz (GHz) and beyond. These units may offer hundreds of channels, programmable memories, and frequency skipping.
Internally, three types of UHF scanner can be found. Older models rely on single-frequency crystal technology; these radios typically do not have keypads, and cannot follow today's trunked radio transmissions. Conventional programmable radios use integrated circuits for tuning more frequency ranges at higher speeds. Trunk tracking programmable systems permit automatic group tuning; transmissions shift frequencies and usually require a dedicated trunking scanner to track conversations across a portion of the band.
Various scanners are combined with Citizens Band (CB) radios and speaker mics for transmitting on 40 channels. Marine radios may be splash proof, and others are outfitted with rugged cases for tough outdoor conditions. Some handheld types combine UHF scanning with very high frequency (VHF) bands to extend capability. Others are capable of hands-free operation, voice scrambling functions, and CTCSS — a continuous tone coded squelch system, which allows listening only to particular senders on a channel.
A UHF scanner legally permits listening to many types of official transmissions. Private telephone or pager transmissions, however, are protected by law, and should not be intentionally intercepted. Scanners may come with accessories such as headphones, cradles, or clip-on antenna mounts, as well as a wide variety of antenna types, from magnetic-mounting to telescoping whips. Others may come with chargers, batteries, or adapters.