A memory channel stores a complete radio setup under one number or name: frequency, mode, repeater offset, tone and more. Scanning steps through frequencies or memories and stops when it hears a signal. Together they turn a radio with hundreds of options into one you can use with a single knob.
Example values only. The scan cursor skips locked-out channels and holds on a busy one.
What a memory remembers
Typically: the receive frequency, the offset and direction for a repeater, the CTCSS or DCS tone, the mode, the power level, and a text name. A repeater memory is worth having because the offset and tone are exactly the details people forget or mistype.
Memory mode versus VFO mode: in VFO mode you tune freely with the dial or keypad; in memory mode the dial just moves between stored channels. On many radios, changes made while in memory mode affect only a temporary copy until you store them.
Most radios keep a call channel or favourite for quick access, and some have separate banks so you can group channels by purpose: local repeaters, simplex, weather, a net.
Memories can be loaded in bulk from a computer, and a code plug is the same idea for digital radios: a file of channels, talkgroups and settings written into the radio. See CAT control and rig software.
The kinds of scan
Scan
Steps through
Use
Memory scan
your stored channels, skipping any marked to skip
monitor your local repeaters and simplex channels
Programmed (band) scan
everything between two limit frequencies, in tuning steps
find activity on a band segment
Priority or dual watch
the current channel, with a periodic check of a priority channel
stay on one conversation without missing a net
Tone scan
the tones on an active signal
find which CTCSS tone a repeater uses
The scanner moves on at a fixed rate until the squelch opens, holds while the signal lasts, then resumes after a pause. A hold that is too short loses the reply to a short transmission; one that is too long delays the next channel. Most radios let you pick time-based or carrier-based resume.
Pitfalls
Scanning relies on the squelch. If it is open, the scan stops on noise at once; set it just above the noise first.
A step size that does not match the band plan skips real channels or lands between them. On VHF FM that is commonly 5, 10, 12.5, 15, 20 or 25 kHz, depending on the region and band plan.
Scanning HF is rarely useful: signals fade, and SSB and CW have no carrier to stop on. It is mainly an FM and VHF/UHF tool.