Unit 1 — Theory of Operation
TM-TOOL-007 — Open Handout TM Chapter: Chapter 2 ELOs: Understand the operating principle of the COMPACT PORTABLE RF POWER METER; identify key specifications Estimated time: 20 minutes
Step 1: Read the TM
Open TM-TOOL-007. Read Chapter 2 — Theory of Operation completely.
Then come back here.
Chapter 2 Content
2-1 Directional Coupler Principle
A toroid transformer (T1) with 1 primary turn (the center conductor of the transmission line) and N secondary turns couples a fraction of the forward and reflected waves. The coupling factor C (dB) = −20 log10(N) for a toroid coupler. Typical values:
| Power range | N2 turns | Coupling | Detector input (at full scale) |
|---|---|---|---|
| 1000W | 32 | −30 dB | 1.0W = 0 dBm |
| 100W | 10 | −20 dB | 100W → 1 mW = 0 dBm |
| 10W | 10 | −20 dB | 10W → 0.1 mW |
| 1W | 3 | −10 dB | 1W → 0.1W |
2-2 Schottky Diode Detector
1N5711 Schottky diodes detect the coupled RF. Forward voltage ~0.25V at low signal levels (square-law region: V_out ∝ P_in) and ~0.4V at high levels (linear region: V_out ∝ V_in). The ADS1115 16-bit ADC samples V_fwd and V_ref; firmware converts to power using a calibration table stored in NVS.
2-3 SWR Computation |Γ| = sqrt(P_ref / P_fwd) SWR = (1 + |Γ|) / (1 − |Γ|)
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 COMPACT PORTABLE RF POWER METER 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 COMPACT PORTABLE RF POWER METER 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 COMPACT PORTABLE RF POWER METER - The primary error source(s) - At least one key specification with its value
→ Proceed to Unit 2