Unit 1 — Theory of Operation

TM-TOOL-004 — Open Handout TM Chapter: Chapter 2 ELOs: Understand the operating principle of the RF DUMMY LOADS — CONSTRUCTION AND USE; identify key specifications Estimated time: 20 minutes

Step 1: Read the TM

Open TM-TOOL-004. Read Chapter 2 — Theory of Operation completely.

Then come back here.

Chapter 2 Content

2-1 Resistor Network Fundamentals

Non-inductive resistors in parallel sets combine power ratings and maintain the 50Ω impedance. For N identical resistors each of value R in parallel: Z = R / N. Use:

• 100W load: 4 × 200Ω 25W resistors in parallel = 50Ω, 100W
• 500W load: 4 × 200Ω 125W in parallel = 50Ω, 500W
• 1 kW load: 8 × 400Ω 125W in parallel = 50Ω, 1000W

2-2 Parasitic Inductance and Frequency Limit

Each resistor lead has approximately 5–10 nH of lead inductance. At 150 MHz: X_L = 2π × 150e6 × 8e-9 = 7.5Ω, causing SWR to rise above 1.5:1. Minimizing lead length to ≤10 mm each side and using star wiring (all high ends bonded to a single center stud) reduces effective inductance to 2-3 Oil Cooling

Transformer oil (mineral oil) provides thermal conductivity of 0.135 W/m·K, approximately 10× better than still air. Resistors submerged in oil can dissipate their full rated power continuously at 25°C ambient. Seal the container; oil expands approximately 7% from 20°C to 100°C.

Why Theory Matters

You cannot use a measurement tool correctly without understanding how it works. Theory tells you: - What the tool measures and how it converts the quantity to a readable output - What the sources of error are — so you can recognize and minimize them - What the valid operating range is — so you stay within its specifications - How to interpret results that don't match expectations

If a measurement looks wrong, theory is where you look first.

Self-Check Questions

SC1-1. In one sentence, state the operating principle of the RF DUMMY LOADS — CONSTRUCTION AND USE as described in Chapter 2.

SC1-2. What does Chapter 2 identify as the primary source(s) of measurement error or uncertainty?

SC1-3. What key specification(s) (accuracy, range, frequency coverage) does the TM state?

SC1-4. What does Chapter 2 say the RF DUMMY LOADS — CONSTRUCTION AND USE cannot do — what are its limitations?

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

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 error sources, accuracy limits, parasitic effects, or frequency dependence.

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

SC1-4. See Chapter 2 and Chapter 1. Limitations are often stated as frequency range, power limits, or accuracy bounds.

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

Checkpoint

Before proceeding, state without looking: - The operating principle of the RF DUMMY LOADS — CONSTRUCTION AND USE - The primary error source(s) - At least one key specification with its value

→ Proceed to Unit 2