Unit 1 — Theory of Operation
TM-CAL-017 — Open Handout TM Chapter: Chapter 2 ELOs: Understand how the reference standard generates or maintains its reference value; identify key specifications Estimated time: 20 minutes
Step 1: Read the TM
Open TM-CAL-017. Read Chapter 2 — Theory of Operation completely.
Then come back here.
Chapter 2 Content
2-1. FAR-FIELD ELECTRIC FIELD STRENGTH
Far-field electric field strength
E (V/m) = √(30 × PW × G) / d
Where PW = transmitter power in watts, G = antenna gain (linear ratio, not dB), d = distance in meters from antenna.
Half-wave dipole gain (linear)
Gdipole = 1.64 (2.15 dBi)
Isotropic antenna gain
Gisotropic = 1.0 (0 dBi)
| Power (W) | Distance (m) | E (V/m) | E (dBμV/m) |
|---|---|---|---|
| 0.1 | 1 | 7.01 | 137 |
| 0.1 | 3 | 2.34 | 127 |
| 1.0 | 3 | 7.40 | 137 |
| 5.0 | 3 | 16.5 | 144 |
| 5.0 | 10 | 4.96 | 134 |
2-2. NEAR FIELD VS. FAR FIELD
The far-field approximation (above) applies only beyond the Rayleigh distance.
Far-field boundary (electrically short antenna)
dfar = λ / (2π) ≈ 0.159 λ
At HF (3–30 MHz), λ = 10–100 m, so far-field begins at 1.6–16 m. Tests at <3 m at HF may be in the near-field where the 1/d law does not hold.
Why Theory Matters for Calibration
You cannot calibrate what you do not understand. Theory tells you: - What the instrument or standard is supposed to do — so you recognize when it is not doing it - What the sources of error are — so you know which ones your calibration procedure addresses - What the limits of the calibration are — so you know when to stop and call it good
If a calibration measurement produces a surprising result, theory is where you look first.
Self-Check Questions
SC1-1. In one sentence, state the operating principle of the FIELD STRENGTH REFERENCE 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, resolution) does the TM state for this standard?
SC1-4. What safety precaution does §1-3 specify? State it exactly.
SC1-5. What references does §1-2 cite? List at least two.
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, uncertainty, drift, or limiting factors.
SC1-3. See Chapter 2. Look for numbers with units: %, ppm, Hz, Ω, dB.
SC1-4. See TM §1-3. Copy the safety text exactly.
SC1-5. See TM §1-2. The references list is there.
Checkpoint
Before proceeding, state without looking: - The operating principle of the FIELD STRENGTH REFERENCE - The primary error source(s) - At least one key specification with its value
→ Proceed to Unit 2