# Demo — Jammer / J/S Explorer
A self-protect jammer's advantage is not constant — it depends on range, and it works *against* the jammer as the target closes. This demo plots the jam-to-signal ratio against range, marks the burn-through point where the radar wins, and shows how stealth shifts that point.
## The ratio
$$
\frac{J}{S} = \frac{4\pi\,P_j G_j\,R^2}{P_t G_t\,\sigma}.
$$
The jammer reaches the radar one-way ($\propto 1/R^2$) while the skin echo is two-way ($\propto 1/R^4$), so $J/S \propto R^2$ — large far out, shrinking as the target closes.
## Interactive demo
Open in full screen
## Walkthrough
1. **Read the curve.** $J/S$ in dB rises with range. The red line is the radar's tolerable threshold; where the curve crosses it is the burn-through range $R_\text{bt}$.
2. **Slide the range cursor.** Beyond $R_\text{bt}$ the jammer buries the return; inside it the radar has burned through and holds the track. Watch the verdict flip.
3. **Cut the RCS.** Lower $\sigma$ and the whole curve lifts — $J/S$ improves everywhere — and $R_\text{bt}$ moves *inward*. Stealth forces the radar to get closer before it can burn through.
4. **Trade jammer power.** Raise $P_j G_j$ and push $R_\text{bt}$ further in; the geometry and the power budget both move the same marker.
## Key observations
- **$J/S \propto R^2$:** the jammer wins far out, the radar burns through close in — the same one-way/two-way asymmetry from L11, now working for the defender of the track.
- **Stealth and jamming compound.** Lower RCS raises $J/S$ and pulls burn-through inward, so LO and EA reinforce each other.
- **Burn-through is inevitable at some range** for a fixed jammer — which is why deception (L18) attacks the *measurement* instead of the power budget.
## Source
MATLAB · code/L17_JtoSBurnThrough.m↓
The in-class script computes $J/S$ versus range for a self-protect jammer, finds the burn-through range, and shows how lowering RCS pulls it inward.