Unit 1 — Theory of Operation

TM-GEAR-016 — Open Handout TM Chapter: Chapter 2 ELOs: Understand the operating principle of the RFI MITIGATION — IDENTIFICATION AND SUPPRESSION; identify key specifications Estimated time: 20 minutes

Step 1: Read the TM

Open TM-GEAR-016. Read Chapter 2 — Theory of Operation completely.

Then come back here.

Chapter 2 Content

2-1 Active Noise Canceller Principle

A reference (auxiliary) antenna is aimed at the local noise source. Its output (mostly noise) is phase-shifted and amplitude-adjusted to match the noise component in the main antenna signal. When subtracted from the main signal, the noise cancels while the desired signal (from a distant direction) is preserved:

V_main = V_signal + V_noise_main V_ref = V_noise_ref (negligible V_signal in reference direction) V_out = V_main − A × e^(jφ) × V_ref ≈ V_signal The phase (φ) and amplitude (A) are adjusted manually or automatically until the noise is minimized. Practical cancellation: 20–40 dB, limited by noise source geometry and antenna placement.

2-2 Near-Field Sniffer Probe

A small shielded loop (30–50 mm diameter) coupled to a SMA connector is held near suspected RFI sources. The loop responds to the magnetic component of the near-field. Connected to an SDR or TinySA, the probe identifies the source and its harmonic spectrum, enabling targeted mitigation (ferrite beads, cable rerouting, shielding).

Why Theory Matters

You cannot build or use RF gear correctly without understanding how it works. Theory tells you: - What the component does and how it produces that effect - What the sources of loss, distortion, or error are — so you can recognize and minimize them - What the valid operating range is — frequency, power, impedance — so you stay within specifications - How to interpret results or system behavior that doesn't match expectations

If a component doesn't perform as expected, theory is where you look first.

Self-Check Questions

SC1-1. In one sentence, state the operating principle of the RFI MITIGATION — IDENTIFICATION AND SUPPRESSION as described in Chapter 2.

SC1-2. What does Chapter 2 identify as the primary source(s) of loss or degradation in performance?

SC1-3. What key specification(s) (frequency range, power rating, insertion loss, impedance ratio) does the TM state?

SC1-4. What does Chapter 2 say the RFI MITIGATION — IDENTIFICATION AND SUPPRESSION cannot do — what are its limitations?

SC1-5. List two formulas or relationships from Chapter 2 that govern the component's behavior.

Answer Key

SC1-1. See TM §2-1. Compare your sentence to the first substantive paragraph of Chapter 2.

SC1-2. See Chapter 2. Look for language about loss mechanisms, parasitic effects, frequency limits, or power constraints.

SC1-3. See Chapter 2. Look for numbers with units: %, dB, Hz, Ω, W, V.

SC1-4. See Chapter 2 and Chapter 1. Limitations are often stated as frequency range, power handling, or impedance range.

SC1-5. See Chapter 2. Equations or proportionality statements are the relationships that govern the component.

Checkpoint

Before proceeding, state without looking: - The operating principle of the RFI MITIGATION — IDENTIFICATION AND SUPPRESSION - The primary loss or degradation source(s) - At least one key specification with its value

→ Proceed to Unit 2