Unit 3 — Assembly and Setup

TM-TOOL-007 — 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-007. Read Chapter 4 — Construction and Assembly completely.

Then come back here.

Chapter 4 Content

4-1 HF Toroid Winding

1. Thread the main transmission line center conductor through the toroid core once (1 primary turn).
2. Wind the secondary winding on the same core: N2 turns (select per Table 2-1 for desired power range). Use #26 AWG Teflon-insulated wire.
3. Wind FWD and REF termination resistors (R1, R2 = 51Ω 1%) directly at the secondary winding ends. Lead length ≤10 mm each.

4-2 PCB Microstrip VHF/UHF Coupler

The microstrip directional coupler for 50–1300 MHz is a PCB structure: two parallel 50Ω microstrip traces (2.9 mm wide on 1.6 mm FR4) separated by a 0.1 mm gap and coupled over a λ/4 length at the band center. Design frequency: 700 MHz (λ/4 at 700 MHz in FR4 = 28 mm). See PCB layout guide for Gerber file dimensions.

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