Unit 4 — Operating Procedures and Calculations

TM-TOOL-005 — 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-005. Read Chapter 5 — Operating Procedures and Appendix A completely.

Then come back here.

Chapter 5 Content

5-1 Antenna Pattern Measurement

  1. Set up a reference transmitter at fixed power and distance from the antenna under test. Distance must be ≥2 × far-field criterion: d_ff = 2D²/λ (D = antenna aperture).
  2. Zero the FSM: rotate the test antenna to maximum signal; note the meter reading as the reference (0 dB or 100%).
  3. Rotate antenna in 15° steps through 360°. Record reading at each step. Compute relative pattern in dB: ΔdB = 20 log10(V/V_ref).
  4. Plot the resulting pattern. Front-to-back ratio, 3 dB beamwidth, and sidelobe levels are directly readable from the plot.

Appendix A — Reference Formulas

E (V/m) = sqrt(P_density_W/m2 × 120π) P_density (W/m2) = P_tx (W) × G_linear / (4π × r2) E (V/m) from dipole: E = sqrt(30 × P_tx × G) / r (far field)

Key Formulas Summary

Key mathematical relationships from Appendix A:

  • E (V/m) = sqrt(P_density_W/m2 × 120π)
  • P_density (W/m2) = P_tx (W) × G_linear / (4π × r2)
  • E (V/m) from dipole: E = sqrt(30 × P_tx × G) / r (far field)

Operating Notes

Chapter 5 specifies 4 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 FIELD STRENGTH METER — CONSTRUCTION AND USE. List steps in order.

P4-2. From Chapter 5: what measurement setting or configuration produces the most accurate result with the FIELD STRENGTH METER — CONSTRUCTION AND USE? 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