Unit 4 — Operating Procedures and Calculations
TM-TOOL-001 — Open Handout TM Chapters: Chapter 5, Appendix A ELOs: Execute operating procedure; interpret readings; compute derived quantities Estimated time: 30 minutes (includes 3–4 practice problems)
Step 1: Read the TM
Open TM-TOOL-001. Read Chapter 5 — Operating Procedures and Appendix A completely.
Then come back here.
Chapter 5 Content
5-1 Watson-Watt Bearing Measurement
- Tune receiver to target signal. Confirm adequate SNR (>20 dB for ±5° accuracy).
- Enable 2-channel sampling. Record V_NS and V_EW amplitude values.
- Compute bearing:
brg = atan2(V_NS, V_EW). Apply declination correction. - Confirm sense: enable sense antenna and verify the 180° correct quadrant.
- Average 10 readings; discard outliers more than 15° from median.
5-2 Butler Matrix Bearing Estimate
- Read RSSI on all four beam ports simultaneously (or in rapid sequence <10 ms total).
- Identify the two highest-RSSI ports (adjacent beams straddle the signal).
- Interpolate: bearing = beam_angle_1 + 45° × (RSSI_1 / (RSSI_1 + RSSI_2)).
- Apply platform heading offset if mounted on a moving vehicle.
Appendix A — Reference Formulas
| Parameter | Watson-Watt | Doppler | Butler 4-el |
|---|---|---|---|
| Accuracy (typical) | ±5° | ±2° | ±3° |
| Min SNR required | 20 dB | 15 dB | 10 dB |
| Multipath sensitivity | High | Medium | Low |
| Moving platform | Poor | Good | Good |
| Hardware complexity | Low | Medium | High |
Key Formulas Summary
Key mathematical relationships from Appendix A:
(See Appendix A in the TM)
Operating Notes
Chapter 5 specifies 9 operating steps.
Measurement discipline: - Always warm up the tool and reference sources before taking readings - Multiple readings improve accuracy — use 3–5 readings and average them - Record every reading with frequency, power level, and settings - A result that seems wrong almost always means a setup error, not a failed tool
Practice Problems
Work these before reading the answer key below.
P4-1. Using the operating procedure from Chapter 5 and the formulas from Appendix A: State the measurement steps you would take to characterize a 40m (7.150 MHz) dipole antenna using the ADF SYSTEMS — ANTENNA DIRECTION FINDING. List steps in order.
P4-2. From Chapter 5: what measurement setting or configuration produces the most accurate result with the ADF SYSTEMS — ANTENNA DIRECTION FINDING? What is the tradeoff if you use a less accurate setting?
P4-3. Chapter 5 specifies an operating procedure for a specific measurement scenario. State the first three steps of that procedure from memory.
P4-4. Appendix A gives a formula for computing a result from measured values. Pick one formula and compute a worked example using made-up but realistic values. Show all work.
Answer Key — Practice Problems
P4-1. Compare your list to Chapter 5. Steps should include: select range/mode → connect antenna → apply signal or enable source → adjust for null/maximum → read and record → compute result.
P4-2. See Chapter 5. The most accurate setting is usually the narrowest bandwidth or highest resolution, at the cost of longer measurement time or reduced range.
P4-3. See Chapter 5, steps 1–3. Copy exactly then close the TM and state from memory.
P4-4. See Appendix A for the formula. Your arithmetic is correct if your result has the right units and is physically plausible.
Checkpoint
Before proceeding: - [ ] You can state the operating procedure from memory (at least the first 5 steps) - [ ] You can compute the derived quantity from Chapter 5 / Appendix A without looking - [ ] You understand what "an unexpected result" tells you about setup
→ Proceed to Unit 5