# Demo — DRFM Deception
Noise jamming shouts at the radar; deception lies to it. A digital RF memory (DRFM) captures the threat's own pulse and replays modified copies that look exactly like real skin returns — and the classic move, range-gate pull-off, walks the radar's tracking gate right off the target. This demo animates that sequence step by step.
## The idea
The radar tracks inside a range gate. A DRFM false return, made brighter than the skin echo, captures the gate, then ramps its delay to drag the gate out in range (recall $R = c\,t/2$). When the false return blinks off, the gate is left coasting on empty space and the true target has slipped free.
## Interactive demo
Open in full screen
## Walkthrough
1. **Press Play and watch the capture.** The DRFM false return (red) sits on the true target (navy) but louder; the tracking gate (blue) locks to the stronger return.
2. **Watch the pull-off.** The false return walks out in range, dragging the gate with it while the true target stays put. The separation readout grows.
3. **Watch the blink.** The false return switches off. The gate is now far downrange on nothing, and the true target is outside it — the lock is broken.
4. **Change the walk-off rate.** A faster pull-off breaks lock sooner but is easier for a deception-aware radar to reject; a slower one is stealthier. Reset and run it again.
## Key observations
- **Deception attacks the measurement, not the power budget.** Unlike noise jamming, it does not have to overpower the echo — it only has to be *believed*.
- **DRFM works because it is coherent.** Replaying the radar's own waveform produces a false return that passes the matched filter as genuine.
- **Every move has a counter.** Leading-edge tracking and other ECCM eventually reject the walked return — the cycle from L11 continues.
## Source
MATLAB · code/L18_RangeGatePullOff.m↓
The in-class script models the tracking gate, captures it with a cover pulse, ramps the false return's delay to walk the gate off the target, then blinks it off so the true target escapes.