Unit 3 — Assembly and Setup

TM-TOOL-005 — 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-005. Read Chapter 4 — Construction and Assembly completely.

Then come back here.

Chapter 4 Content

4-1 Passive FSM

  1. Mount 1N34A diode cathode toward meter positive terminal. R_load = 100 kΩ; C_filter = 10µF 16V electrolytic. Meter series resistance sets FSD.
  2. Connect probe antenna (50 cm rigid copper rod) via BNC to diode anode.

  3. Mount in a small plastic enclosure. Keep RF lead from BNC to diode 4-2 AD8307 Digital FSM

  4. Mount AD8307 with 100 nF NP0 decoupling on each supply pin. INHI connects via 1 nF DC-blocking cap to SMA input; INLO to ground.

  5. VOUT pin (25 mV/dB slope, intercept −84 dBm) connects to ESP32 ADC GPIO (12-bit, 3.3V range). Scale: 3300 mV / 25 mV/dB = 132 dB dynamic range from ADC alone, but ADC noise floor limits practical range to ~80 dB.
  6. Add 10 kΩ + 100 nF low-pass filter between VOUT and ESP32 ADC to reject RF on the DC output line.

Assembly Quality

Chapter 4 specifies 6 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