# L37 Pre-flight **Block 4: Aircraft Survivability and Mission Planning — Lesson 37: Modern Trends in EW** *Work this before L37. Pre-flights are never collected — in class, anyone may be cold-called to present any question at the board, and that recitation is the participation grade.* --- ## Assumed pre-class reading - L2's free-space path loss, $L_\text{fs} = 20\log_{10} R_\text{km} + 20\log_{10} f_\text{GHz} + 92.45$; L8's $P_d$/$P_{fa}$ trade and the ROC; L12's threat library; L16's processing gain and $(\text{J/S})_\text{after} \approx (\text{J/S})_\text{in} - G_p$. - The Jupyter Book Reading page for L37 — the cognitive-EW loop (sense → learn → adapt), reading an emitter classifier's confusion matrix as $P_d$ and $P_{fa}$, GPS below the noise and the jammer's denial radius, INS drift on a denied leg, and uplink versus downlink jamming. --- ## Quiz questions (5 items, ~5 minutes) **Q1.** (Multiple choice) A notional GPS receiver sees the L1 C/A signal (1575.42 MHz) at $-130$ dBm and tolerates a J/S of 30 dB. A jammer with an ERP of 3 W toward it sits 100 km away in free space. The J/S at the receiver, and the verdict, are: - [ ] (a) −11.6 dB — the jammer sits far below the signal, so lock holds easily - [ ] (b) −1.6 dB — the jammer arrives a little weaker than the signal, so lock holds - [ ] (c) 28.4 dB — louder than the signal but under the threshold, so lock holds - [ ] (d) 32.3 dB — 2.3 dB past the threshold, so the receiver loses lock --- **Q2.** (Multiple choice) A GPS jammer denies a circle of some radius around itself. Its ERP is then **quadrupled**. An aircraft crosses the new circle straight through its center at the same speed, on a notional INS that drifts at a constant rate. Compared with crossing the old circle, the denial radius and the INS error at the exit: - [ ] (a) Both grow by $\sqrt{2}$, because range goes as the fourth root of power - [ ] (b) Both double, because a one-way path loses power as $R^2$ - [ ] (c) Both quadruple, because J/S at a fixed range grows in step with the ERP - [ ] (d) The radius doubles, and the error grows fourfold with the squared time --- **Q3.** (Multiple choice) A notional emitter classifier is tested on 50 intercepts of each true emitter type. Rows are the true type; columns are what the classifier said. | True | said EW | said ACQ | said TTR | |---|---|---|---| | EW | 45 | 3 | 2 | | ACQ | 4 | 40 | 6 | | TTR | 2 | 3 | 45 | Treat "TTR" — a tracking radar, the call the aircrew cares about most — as the detection. The classifier's $P_d$ and $P_{fa}$ for TTR are: - [ ] (a) $P_d = 0.85$ and $P_{fa} = 0.15$ - [ ] (b) $P_d = 0.90$ and $P_{fa} = 0.08$ - [ ] (c) $P_d = 0.90$ and $P_{fa} = 0.10$ - [ ] (d) $P_d = 0.87$ and $P_{fa} = 0.13$ --- **Q4.** (Multiple choice) An adversary wants to deny a military satellite-communications network across an entire theater with **one** ground jammer. The satellite is a simple bent-pipe relay. What must the jammer do? - [ ] (a) Jam the uplink from inside the satellite's receive beam, so the relay carries the jam to every user - [ ] (b) Jam the downlink from any one site in the theater, since the downlink reaches every user at once - [ ] (c) Jam the uplink from anywhere in view of the satellite, since its antenna hears all of Earth equally - [ ] (d) Jam the uplink from beside the users, since uplink jamming only hurts terminals near the jammer --- **Q5.** (Short answer) (i) Name the three steps of the cognitive-EW loop and say what each does. (ii) Explain why an RWR that classifies against a fixed threat library fails against an agile, software-defined radar. (iii) An ML emitter classifier trained on three emitter types meets a fourth type it has never seen. What does it report, and why is that dangerous?