Unit 3 — Assembly and Setup

TM-TOOL-009 — 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-009. Read Chapter 4 — Construction and Assembly completely.

Then come back here.

Chapter 4 Content

4-1 Stacking Order

Connect SDR interface modules in this order from antenna to SDR:

Antenna → Bias-T (if using remote LNA) → Preselector → Attenuator/LNA (optional) → HF Upconverter (HF only) → RTL-SDR 4-2 Preselector Band Selection The ESP32 selects the correct filter automatically if configured with the current receive frequency. Manual override: set GPIO[3:0] to the filter index (0–15) using the CYD touchscreen or serial command BAND.

4-3 Upconverter LO Alignment

The RTL-SDR must be told to offset the displayed frequency by the LO value. In SDR# or GQRX: set “LO offset” or “frequency correction” to +125.000 MHz. In GNU Radio: subtract 125e6 from the reported frequency to get the true HF frequency.

Assembly Quality

Work through all construction steps in Chapter 4 in sequence.

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