Unit 3 — Assembly and Setup

TM-GEAR-016 — 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-016. Read Chapter 4 — Construction and Assembly completely.

Then come back here.

Chapter 4 Content

4-1 Active Noise Canceller

  1. Build the ERA-3SM preamplifier: MMIC in SOT-143 package, bias via 130Ω resistor from +9V, input/output 100 pF DC-block caps.
  2. Build the phase shifter: an all-pass filter network using a varactor diode (BB515 or SMV1248) whose capacitance is set by a 0–10V control voltage. This provides 0–360° phase range across the HF band.
  3. Build the subtractor: TL072 dual op-amp configured as a differential amplifier. Gain set by 10 kΩ / 10 kΩ resistors (gain = 1). Apply main signal to non-inverting input; reference signal (after phase shift and attenuation) to inverting input.

4-2 Near-Field Sniffer Probe

  1. Wind a 3-turn loop of RG-174 coax, 35 mm diameter. Connect the shield at both ends to the outer conductor of the SMA connector; connect the center conductor at one end only to the SMA center pin. (The shield gap should be at the midpoint of the loop to form a Faraday-shielded loop; solder a jumper to close the shield everywhere except the deliberate gap.)

Assembly Quality

Chapter 4 specifies 4 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