Unit 1 — Theory of Operation
TM-CAL-016 — 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-016. Read Chapter 2 — Theory of Operation completely.
Then come back here.
Chapter 2 Content
2-1. HALF-WAVE DIPOLE RESONANCE
Free-space half-wave dipole resonant frequency
fr (MHz) = 150 / Lm
With end effect (velocity factor ~0.95 for wire)
fr (MHz) = 142.5 / Lm or fr (MHz) = 468 / Lft
Where L is the total tip-to-tip length. At resonance, feedpoint impedance is approximately 70–73 Ω in free space; ground effects reduce this to 20–50 Ω near ground. Height above ground affects both resonant frequency (lowered slightly) and feedpoint impedance.
| Total Length (m) | Total Length (ft) | Resonant Freq (MHz) | Band |
|---|---|---|---|
| 20.07 | 65.8 | 7.1 | 40m CW |
| 10.03 | 32.9 | 14.2 | 20m SSB |
| 6.69 | 21.9 | 21.3 | 15m |
| 4.78 | 15.7 | 29.8 | 10m |
| 2.00 | 6.56 | 71.3 | 4m/VHF |
2-2. NANOVANA MEASUREMENT
The NanoVNA measures complex impedance Z = R + jX. At resonance: X = 0 (or near zero). The resonant frequency is observed as the zero-crossing of the reactance curve, or as the minimum of |S11|.
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 KNOWN-LENGTH DIPOLE 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 KNOWN-LENGTH DIPOLE STANDARD - The primary error source(s) - At least one key specification with its value
→ Proceed to Unit 2