Unit 3 — Assembly and Setup

TM-TOOL-006 — Open Handout TM Chapter: Chapter 4 ELOs: Execute assembly steps in the correct sequence; verify build quality before operation Estimated time: 20 minutes

Step 1: Read the TM

Open TM-TOOL-006. Read Chapter 4 — Construction and Assembly completely.

Then come back here.

Chapter 4 Content

4-1 Transformer Winding

  1. Wind three identical windings of 6 turns #26 AWG simultaneously on a BN-43-202 binocular core. Keep the three windings in the same rotational direction (color-code the wire starts).
  2. Check winding: with an ohmmeter, verify all three windings are equal resistance (±0.1Ω) and have no shorts between windings.
  3. Test leakage inductance: connect one winding to NanoVNA port 1 with port 2 shorted to the other two windings. Leakage inductance should be 4-2 Calibration Dials

Mark the R_cal potentiometer dial in 10Ω steps from 0 to 200Ω using a resistance meter. Mark the X_cal capacitor dial in terms of −jX at 10 MHz using the formula X_C = 1/(2πfC). Mark the inductor in terms of +jX at 10 MHz using X_L = 2πfL. Actual X depends on operating frequency; provide a reactance chart (see Appendix A) for other frequencies.

Assembly Quality

Chapter 4 specifies 3 construction/assembly steps.

The assembly directly determines measurement quality. Common errors: - RF leads too long — lead inductance raises SWR and limits high-frequency performance - Cold solder joints on RF nodes — high resistance causes signal loss and intermittent readings - Ground loops — multiple ground paths at different potentials cause noise and calibration errors - Ferrite winding errors — wrong turn count or direction reverses transformer polarity

If Chapter 4 specifies a verification step after assembly (e.g., "verify DC resistance = X before proceeding"), do it. Those checks exist because they are the most common failure points.

Self-Check Questions

SC3-1. How many assembly steps does Chapter 4 specify?

SC3-2. What is the first assembly step? State it exactly from the TM.

SC3-3. Does Chapter 4 specify maximum lead length anywhere? If so, what is the limit and why?

SC3-4. Does Chapter 4 require a bench verification after assembly? What does it check?

SC3-5. What would you do if a winding resistance measurement came out wrong during assembly verification?

Answer Key

SC3-1. Count the numbered steps in Chapter 4.

SC3-2. See Chapter 4, step 1. Copy it exactly.

SC3-3. RF lead length limits are typically 10–15 mm for HF circuits. Longer leads add ~1–2 nH per mm, raising inductive reactance at high frequencies.

SC3-4. Scan Chapter 4 for verification steps. Common checks: DC resistance, winding balance, null depth on test signal.

SC3-5. Stop assembly. Diagnose before proceeding — a winding error found before completion is much easier to fix than one discovered after the unit is boxed.

Checkpoint

Before proceeding: - [ ] You have read Chapter 4 completely - [ ] You can state the number of assembly steps and the first and last steps - [ ] You understand how assembly quality affects measurement accuracy

→ Proceed to Unit 4