Unit 4 — Operating Procedures and Calculations
TM-TOOL-006 — 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-006. Read Chapter 5 — Operating Procedures and Appendix A completely.
Then come back here.
Chapter 5 Content
5-1 Measuring Antenna Impedance
- Connect antenna to ANT BNC. Connect communications receiver (tuned to a clear frequency in the antenna's operating range) to DET BNC.
- Enable noise source (power switch ON). Receiver S-meter should show S3–S7 noise level. If no noise: check battery, MMIC bias.
- Set R_cal to 50Ω (center scale) and X_cal to zero (cap at minimum, inductor at minimum).
- Adjust R_cal for minimum S-meter reading. Note: the null may be sharp; sweep slowly.
- If null is imperfect at all R_cal values, the antenna has significant reactance. Adjust X_cal (capacitive for a high-SWR dipole that is too long; inductive for one that is too short) until the null is satisfactorily deep (≥10 dB below noise floor).
- Read R and X from the calibration dials. Reported impedance: Z_ant = R_cal + jX_cal at the measurement frequency.
Appendix A — Reference Formulas
| Component | 1 MHz | 7 MHz | 14 MHz | 28 MHz |
|---|---|---|---|---|
| 47 pF cap | −3386Ω | −484Ω | −242Ω | −121Ω |
| 100 pF cap | −1592Ω | −227Ω | −114Ω | −57Ω |
| 1 µH inductor | +6.3Ω | +44Ω | +88Ω | +176Ω |
| 10 µH inductor | +63Ω | +440Ω | +879Ω | +1759Ω |
Key Formulas Summary
Key mathematical relationships from Appendix A:
(See Appendix A in the TM)
Operating Notes
Chapter 5 specifies 6 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 RF NOISE BRIDGE — IMPEDANCE MEASUREMENT. List steps in order.
P4-2. From Chapter 5: what measurement setting or configuration produces the most accurate result with the RF NOISE BRIDGE — 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