Listen-only by design. The DF-04 never transmits. It reads the drone link that is already in the air, converts it into a bearing, and hands the operator a target list — which keeps the site radio-quiet and the operator undetectable while monitoring is underway. Inside the Detection Chain 01 — Wideband capture The SDR front end scans the 300MHz-6GHz span in three switchable segments, so analogue FPV links and modern frequency-hopping control links arrive on the same receiver.