Unit 1 — Theory of Operation
TM-CAL-013 — 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-013. Read Chapter 2 — Theory of Operation completely.
Then come back here.
Chapter 2 Content
2-1. COAX CAPACITANCE
The capacitance per unit length of coaxial cable is determined by the dielectric constant of the insulation and the conductor geometry:
Capacitance per unit length
C/l = 2πε0εr / ln(D/d)
where D = inner diameter of outer conductor, d = outer diameter of center conductor, εr = relative permittivity of dielectric.
| Cable Type | pF/ft | pF/m | VF | Z0 |
|---|---|---|---|---|
| RG-58A/U | 28.5 | 93.5 | 0.66 | 50 Ω |
| RG-174/U | 26.0 | 85.3 | 0.66 | 50 Ω |
| RG-8X (mini-8) | 26.0 | 85.3 | 0.78 | 50 Ω |
| RG-213/U | 29.0 | 95.1 | 0.66 | 50 Ω |
| RG-6 (75 Ω) | 16.0 | 52.5 | 0.82 | 75 Ω |
| LMR-400 | 23.9 | 78.4 | 0.85 | 50 Ω |
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 COAX CABLE CAPACITANCE STANDARD 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 COAX CABLE CAPACITANCE STANDARD - The primary error source(s) - At least one key specification with its value
→ Proceed to Unit 2