Unit 3 — Assembly and Setup

TM-GEAR-013 — 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-013. Read Chapter 4 — Construction and Assembly completely.

Then come back here.

Chapter 4 Content

4-1 Linear Supply Heatsink Sizing

The series-pass transistors dissipate: P = (V_in − V_out) × I_out. At worst case (13.8V output from 18V rectified): P = (18 − 13.8) × 30 = 126W. With four 2N3055s, each dissipates 31.5W. 2N3055 thermal resistance junction-to-case: RΘjc = 1.5°C/W. Required heatsink resistance: RΘsa ≤ (T_j_max − T_a) / P − RΘjc = (150 − 50) / 31.5 − 1.5 = 1.7°C/W per transistor.

4-2 SMPS EMI Filtering

  1. Install an IEC inlet filter (common-mode choke + X/Y capacitors) on the AC input before the SMPS. This keeps SMPS switching noise off the mains.
  2. Add a ferrite bead choke (2 turns of DC output cable through #31 toroids) on the DC output to suppress conducted emissions from reaching the transceiver.
  3. For receivers: use the linear supply; the SMPS may interfere with sensitive RX even with filtering.

Assembly Quality

Chapter 4 specifies 3 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