Unit 3 — Assembly and Setup

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

Then come back here.

Chapter 4 Content

4-1 Toroidal Coaxial Choke

  1. Stack two FT-240-31 toroids (same orientation). Secure with a cable tie around the outside.
  2. Thread RG-303 (or RG-58) coax through the stacked cores 12 times. Keep passes parallel and tight; each pass reduces the impedance uniformity slightly, so 12 is the practical maximum.
  3. Mount in a weatherproof enclosure at the antenna feedpoint. Connect input coax to radio-side SO-239; output coax to antenna.

4-2 Snap-On Bead Choke

  1. Open 6 type #31 snap-on ferrite beads (Laird 28A0300-0A2 or equivalent).
  2. Snap all 6 beads onto the coax at the feedpoint, positioned within 100 mm of the antenna connection. Close each bead securely.
  3. Secure the bead cluster with a cable tie or wrap of self-amalgamating tape.

Assembly Quality

Chapter 4 specifies 6 construction/assembly steps.

The assembly directly determines RF performance. 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 behavior - Ground loops — multiple ground paths at different potentials cause noise and calibration errors - Ferrite winding errors — wrong turn count or direction reverses transformer polarity or changes impedance ratio - Incorrect winding direction on toroidal transformers — affects phase and common-mode rejection

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, impedance ratio.

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 RF performance

→ Proceed to Unit 4