Unit 4 — Operating Procedures and Calculations

TM-TOOL-002 — 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-002. Read Chapter 5 — Operating Procedures and Appendix A completely.

Then come back here.

Chapter 5 Content

5-1 SWR Sweep

  1. Connect antenna to DUT port (SMA). Select band (HF or VHF/UHF).
  2. Enter start/stop frequency and number of sweep points (101 or 201).
  3. Press SWEEP. The display plots SWR vs. frequency in real time.
  4. Identify the resonance (SWR minimum). Press MARKER; the instrument displays f_res, SWR, R, X at the marker frequency.

5-2 Smith Chart Display

  1. Select SMITH mode. The sweep traces the impedance locus on the Smith chart.
  2. Clockwise rotation with increasing frequency = capacitive reactance dominant (antenna too short). Counter-clockwise = inductive (antenna too long).
  3. At resonance, the locus crosses the real axis; R at crossing = feedpoint resistance. Ideal dipole: 72Ω (free space), lower over ground.

Appendix A — Reference Formulas

SWR = (1 + |Γ|) / (1 − |Γ|) |Γ| = (SWR − 1) / (SWR + 1) Return loss (dB) = −20 log10(|Γ|) Z_ant = 50 × (1 + Γ) / (1 − Γ) [complex arithmetic]

Key Formulas Summary

Key mathematical relationships from Appendix A:

  • SWR = (1 + |Γ|) / (1 − |Γ|)
  • |Γ| = (SWR − 1) / (SWR + 1)
  • Return loss (dB) = −20 log10(|Γ|)
  • Z_ant = 50 × (1 + Γ) / (1 − Γ) [complex arithmetic]

Operating Notes

Chapter 5 specifies 7 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 ANTENNA ANALYZER — VECTOR IMPEDANCE MEASUREMENT. List steps in order.

P4-2. From Chapter 5: what measurement setting or configuration produces the most accurate result with the ANTENNA ANALYZER — VECTOR IMPEDANCE MEASUREMENT? 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