Also known as: conventional radio
Conventional radio assigns each user group its own fixed frequency, in contrast to trunked radio.1 A conversation always happens on the same channel, so there is no control channel to coordinate assignments and no channel grant to follow — you simply tune to the frequency you want.
How it works
Groups transmit on their assigned simplex frequency or through a repeater pair (mobiles transmit on an input frequency, the repeater retransmits on an output frequency to extend range). To keep unrelated users off the same channel, conventional systems commonly layer a sub-audible squelch tone or code — CTCSS or DCS — so a receiver only opens its speaker for its own group. Digital conventional modes achieve the same selectivity with a color code, network access code, or radio access number.
The architecture is simple and robust because there is no central controller to fail: if one channel’s repeater goes down, only that channel is affected. The cost is spectrum efficiency — each frequency sits idle whenever its group is quiet, so serving N groups requires close to N channels regardless of how little any one of them talks.
Variants
- Simplex — radios transmit and receive on one frequency, talking directly unit to unit with no infrastructure.
- Repeater (duplex) — a fixed repeater rebroadcasts traffic to cover a wider area; the input/output pair is still one logical channel.
- Analog vs. digital — analog FM with CTCSS/DCS, or digital modes like DMR Tier II and NXDN conventional, which add unit IDs and text without a trunking controller.
In practice
Conventional operation remains common for amateur radio, business licensees, aviation, marine VHF, and smaller public-safety agencies that do not need the capacity of a trunked network. It is also the fallback for trunked systems: when a site loses its controller, failsoft mode reverts each channel to conventional repeater operation so local users keep talking. A monitor that knows a system’s frequency list can cover it with a simple priority-ordered scan.
Relevance to SDR
Conventional channels are scanned directly by tuning to the known frequency — no grant-following required, which makes them the easiest traffic to capture with an SDR. GopherTrunk can log and play conventional analog and digital channels alongside the trunked systems it tracks; the two coexist because a monitored region usually mixes both. DMR Tier II is a widely deployed digital conventional example.
Sources
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Two-way radio — Wikipedia, on fixed-frequency conventional two-way radio operation. ↩