Unit 1 — Theory of Operation

TM-TOOL-008 — Open Handout TM Chapter: Chapter 2 ELOs: Understand the operating principle of the RF POWER METERS — TYPES AND OPERATION; identify key specifications Estimated time: 20 minutes

Step 1: Read the TM

Open TM-TOOL-008. Read Chapter 2 — Theory of Operation completely.

Then come back here.

Chapter 2 Content

2-1 Bird Model 43 Slug Type

The Bird 43 is an inline directional wattmeter using interchangeable plug-in elements (slugs). Each slug contains a toroid directional coupler wound for a specific frequency range and power range. The slug's flat face orientation determines forward vs. reflected reading: flat toward the meter face = forward power; flat away = reflected. Output is a DC voltage proportional to forward (or reflected) power, driving an analog panel meter.

Slug PCB dimensions: 25.0 mm OD × 25.4 mm length. Retention: O-ring at body midpoint. Contact: 2 mm banana pin. The flatted-D cross-section prevents 90° orientation errors.

2-2 Inline Directional Meter

Uses a toroid coupler (1-turn primary = center conductor; N-turn secondary) plus Schottky diode detectors (1N5711) for forward and reflected channels. An ADS1115 16-bit I2C ADC digitizes both channels; ESP32 computes forward power, reflected power, and SWR in firmware. CYD display shows real-time readings. Typical frequency range 1.8–600 MHz with appropriate coupler design.

2-3 Terminating Wattmeter

A terminating wattmeter absorbs all transmitted power in an internal 50Ω load (dry or oil-cooled) and measures the absorbed power via a coupler before the load. Because there is no transmitted power beyond the instrument, no antenna is needed during testing. Used for final amplifier output power verification and transmitter tuning.

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 POWER METERS — TYPES AND OPERATION 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 POWER METERS — TYPES AND OPERATION 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 POWER METERS — TYPES AND OPERATION - The primary error source(s) - At least one key specification with its value

→ Proceed to Unit 2