The eight signal classes

Nothing here is specific to any manufacturer. The classes below are a property of how aircraft are built and flown, not of any product that watches for them. The last one is the class no radio receiver can see, including ours.

Signal class	What flies on it	What a receiver has to do
Remote ID broadcast	Commercially manufactured aircraft flown in compliance with the rules	Receive Wi-Fi and Bluetooth and parse a published message format. The aircraft is cooperating, so this is the least demanding class.
Commercial control downlink	Consumer and professional aircraft from the dominant manufacturer, including flights with Remote ID absent or disabled	Identify a proprietary control and video protocol in the 2.4 and 5.8 GHz bands. Newer implementations are encrypted, which separates detecting a flight from identifying the airframe.
Wi-Fi and Bluetooth control	Lower-cost and toy-class aircraft controlled from a phone or tablet	Distinguish an aircraft control session from ordinary consumer traffic on the same crowded bands.
Open control links	Hand-built and long-range aircraft using open-source radio control systems	Demodulate open protocols across several bands. These are documented, but they are not Wi-Fi and a Remote ID receiver will not see them.
Analog FPV video	Racing and hand-built first-person-view aircraft	Detect analog video carriers, typically in the 5 GHz race bands. There is no identifier in the signal at all — the presence of the carrier is the detection.
Digital FPV video	Newer first-person-view aircraft using digital video systems	Recognise a digital video downlink that looks nothing like Wi-Fi and carries no compliance identifier.
Telemetry links	Aircraft carrying a separate data link for flight information, common on hand-built and industrial platforms	Demodulate telemetry protocols, frequently on 900 MHz, which is a different band and a different receiver from everything above.
No RF emission	Fully autonomous aircraft flying a pre-loaded route with the transmitter off, and unpowered aircraft	Nothing. There is no signal to receive. No radio-frequency instrument detects this class, ours included. Radar, acoustic, or optical sensing is the answer, and each has its own limits.

Two things follow from the table. Coverage is a hardware question before it is a software question, because most of these classes sit in different bands and need a receiver tuned to them. And no single sensing technology covers all eight, which is why the last row matters: an instrument that does not tell you what it cannot see is not telling you what it can.

Approaches to detection

Detection systems are built around different sensing approaches. Each has real strengths, and each has boundaries that follow from the design rather than from the quality of the engineering. Knowing which approach a system takes tells you more than a feature list does.

None of these is wrong. They answer different questions, and a site with a serious problem often ends up running more than one. What matters is knowing which question a given instrument answers before it is specified into a budget.

Questions worth asking about any system

Whoever you are evaluating, including us.

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Passive RF detection and situational awareness only. Performance varies by RF environment, antenna placement, aircraft type, and deployment configuration. Terms and policies.