Unit 1 — Theory of Operation

TM-TOOL-005 — Open Handout TM Chapter: Chapter 2 ELOs: Understand the operating principle of the FIELD STRENGTH METER — CONSTRUCTION AND USE; identify key specifications Estimated time: 20 minutes

Step 1: Read the TM

Open TM-TOOL-005. Read Chapter 2 — Theory of Operation completely.

Then come back here.

Chapter 2 Content

2-1 Passive Detector

An RF signal intercepted by the probe antenna develops a voltage across a germanium point-contact diode (1N34A). The diode rectifies the RF to DC; a 10µF capacitor integrates (smooths) the rectified DC; a 100µA FSD panel meter displays the result. Sensitivity is limited by the diode forward voltage (~0.2V for germanium vs. ~0.6V for silicon); minimum detectable field from a 50 cm whip at 7 MHz is approximately 0.5 mV/m.

2-2 Active Version

A common-base RF amplifier (BF199 or 2N3904) precedes the detector diode, providing 20–30 dB of gain before detection. An op-amp (LM386 or similar) drives a meter with logarithmic compression for a dB-proportional scale. Sensitivity improves to approximately 5 µV/m.

2-3 Digital CYD FSM

An AD8307 logarithmic amplifier (0.1–500 MHz, −74 to +17 dBm, 25 mV/dB) replaces the detector and meter. Its output drives an ESP32 ADC; the CYD display shows field strength in dBm (relative to 50Ω) and logs readings with GPS timestamp. Absolute calibration ties the ADC reading to a known field (calibrated reference transmitter at known distance).

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 FIELD STRENGTH METER — 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 FIELD STRENGTH METER — 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 FIELD STRENGTH METER — CONSTRUCTION AND USE - The primary error source(s) - At least one key specification with its value

→ Proceed to Unit 2