Unit 4 — Operating Procedures and Calculations

TM-GEAR-015 — Open Handout TM Chapters: Chapter 5, Appendix A ELOs: Install and operate the RF DIRECTIONAL COUPLERS — CONSTRUCTION AND CALIBRATION correctly; interpret performance data; compute derived quantities Estimated time: 30 minutes (includes 3–4 practice problems)

Step 1: Read the TM

Open TM-GEAR-015. Read Chapter 5 — Operating Procedures and Appendix A completely.

Then come back here.

Chapter 5 Content

Directional couplers are passive devices; no operational procedure is required beyond installation. Install the coupler inline between the transmitter and the antenna (or load under test). Connect VFWD and VREF outputs to the meter or ADC inputs.

• Never exceed the power rating of the coupler (determined by the center conductor rating and connector type).
• Do not operate with the VFWD or VREF ports open (floating) — load them with ≥50 kΩ (meter input) to prevent undefined voltage states.

Appendix A — Reference Formulas

Bruene toroidal coupler, BN-43-202: Coupling factor C (dB) = -20 log10(N2) N2 = 10 turns: C = -20 dB N2 = 20 turns: C = -26 dB (standard design) N2 = 30 turns: C = -30 dB

More turns = weaker coupling = smaller VFWD/VREF output voltage. For a 1W signal into 50Ω (V_line = sqrt(50) = 7.07V pk): At N2=20: V_coupled = 7.07 / 20 = 0.35V pk → after diode: ~0.15V DC

Key Formulas Summary

Key mathematical relationships from Appendix A:

• Coupling factor C (dB) = -20 log10(N2)
• N2 = 10 turns: C = -20 dB
• N2 = 20 turns: C = -26 dB (standard design)
• N2 = 30 turns: C = -30 dB
• More turns = weaker coupling = smaller VFWD/VREF output voltage.
• For a 1W signal into 50Ω (V_line = sqrt(50) = 7.07V pk):

Operating Notes

Work through all steps in Chapter 5 in sequence.

Installation and operating discipline: - Always verify polarity and orientation before making connections — RF transformers and baluns are phase-sensitive - Route feedlines away from parallel conductors — parallel runs create mutual coupling that degrades isolation - Ground all exposed metalwork at a single chassis point — multiple grounds create loops - Record settings, frequencies, and power levels for every test — you need baseline data for comparisons

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 installation steps you would take to put the RF DIRECTIONAL COUPLERS — CONSTRUCTION AND CALIBRATION in service on a 40m (7.150 MHz) station. List steps in order.

P4-2. From Chapter 5: what installation or setup detail produces the best RF performance with the RF DIRECTIONAL COUPLERS — CONSTRUCTION AND CALIBRATION? What is the tradeoff if you omit or shortcut that step?

P4-3. Chapter 5 specifies an operating procedure for a specific use case. 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 mounting location → connect to feedline/antenna → verify polarity/orientation → apply power or signal → verify operation → record baseline.

P4-2. See Chapter 5. The most important installation detail is usually physical orientation, lead length, or ground bonding — the tradeoff if omitted is degraded isolation, increased SWR, or common-mode current leakage.

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 a degraded or unexpected result tells you about the installation

→ Proceed to Unit 5