Unit 4 — Operating Procedures and Calculations
TM-TOOL-003 — 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-003. Read Chapter 5 — Operating Procedures and Appendix A completely.
Then come back here.
Chapter 5 Content
5-1 Running the Engine
from nec_runner import NECRunner, NECEngine runner = NECRunner(engine=NECEngine.NEC2) result = runner.run(model) if not result.success: print(result.stderr) The runner writes a temporary .nec file, invokes nec2c as a subprocess, captures stdout/stderr, and returns a NECResult object. Timeout default: 60 seconds (adjustable for large sweeps).
5-2 Parsing Output from nec_parser import NECOutputParser parser = NECOutputParser() points = parser.parse(result.output_file)
points: list of {freq_mhz, gain_dbi, z_real, z_imag, swr, theta, phi}
Appendix A — Reference Formulas
| Error | Cause | Fix |
|---|---|---|
| SEGMENT FAILURE | Wire too short for segment count | Reduce min_segs or increase length |
| Impedance = 0+j0 | Source on wrong tag/segment | Verify EX card tag matches GW tag |
| Gain >30 dBi | Wire below ground (Z 2 × radius |
Key Formulas Summary
Key mathematical relationships from Appendix A:
| Impedance = 0+j0 | Source on wrong tag/segment | Verify EX card tag matches GW tag |
Operating Notes
Work through all steps in Chapter 5 in sequence.
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 NEC ANTENNA MODELING SYSTEM. List steps in order.
P4-2. From Chapter 5: what measurement setting or configuration produces the most accurate result with the NEC ANTENNA MODELING SYSTEM? 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