Unit 2 — Materials and Construction
TM-ANT-072 — Open Handout TM Chapter: Chapter 3 ELOs: Identify and gather all required materials; understand why each material is specified Estimated time: 20 minutes
Step 1: Read the TM
Open TM-ANT-072. Read Chapter 3 — Materials and Construction completely.
Then come back here.
Chapter 3 Content
3-1. BILL OF MATERIALS
| Qty | Item | Specification |
|---|---|---|
| 1 | Vertical element | Aluminum tubing 1–1.5 in OD or #12 AWG copper wire; length per formula |
| Per design | Radials | #16–#14 AWG copper; per ground system design above |
| 1 | Mast/base insulator | UV-resistant PVC or polycarbonate; must support element tension/weight |
| 1 | SO-239 or N-type connector | Weatherproof; mount at base |
| 1 | Feed line | RG-213 or LMR-400 for permanent install; RG-8X for portable use |
| As needed | Loading coil (if loaded vertical) | T-200 toroidal core or air-wound; Ql > 200 for minimum loss |
3-2. DIMENSION FORMULAS
Quarter-wave vertical height (feet)
L = 234 / fMHz
Example: 40M at 7.150 MHz
L = 234 / 7.150 = 32.7 ft
Resonant radial length (each radial, feet)
Lrad = 246 / fMHz (resonant elevated radials)
Loading coil inductance for shortened element
L (μH) = Z0 × (1 − cos(θ)) / (2πf × sin(θ)) where θ = electrical length of element
Material Selection
Review the full materials list in Chapter 3.
Before building, verify every item on the materials list. Key considerations: - Wire gauge affects conductor resistance and therefore efficiency — use the specified gauge or heavier - Coax type affects velocity factor, which changes electrical length vs. physical length - Ferrite core type (#43, #61, #67) is frequency-specific for matching transformers and chokes - Connector types affect impedance continuity — SO-239, N, BNC, and SMA each have frequency limits - Insulator material and placement affect wind loading and UV degradation
The materials list in Chapter 3 is the bill of materials for a tested, working antenna. Substitutions must be evaluated, not assumed equivalent.
Self-Check Questions
SC2-1. List the three most critical materials or components specified in Chapter 3. Why are they critical?
SC2-2. What wire gauge does Chapter 3 specify? What is the consequence of using a smaller gauge?
SC2-3. If Chapter 3 specifies coaxial cable, what type is called for? What is its velocity factor?
SC2-4. Does Chapter 3 specify a particular ferrite or core type? What is its application in this antenna?
SC2-5. What is the consequence of using a connector type outside its rated frequency range?
Answer Key
SC2-1. See Chapter 3. Identify items with specific part numbers, gauge specifications, or where substitution would change resonant frequency or impedance.
SC2-2. See Chapter 3. Smaller gauge = higher conductor resistance = lower efficiency and greater I²R losses.
SC2-3. See Chapter 3. Common types: RG-58 (0.66 VF), RG-8X (0.84), LMR-400 (0.85). Velocity factor changes electrical length: physical length = λ × VF.
SC2-4. See Chapter 3. Type #43 ferrite is general HF (1–50 MHz); #61 for upper HF/VHF; #67 for VHF. Wrong material means wrong impedance ratio at the operating frequency.
SC2-5. A connector used beyond its frequency rating introduces unpredictable impedance discontinuities, increasing reflected power and SWR.
Checkpoint
Before proceeding: - [ ] You have read Chapter 3 completely - [ ] You can name the critical materials from memory - [ ] You have sourced or confirmed availability of all required materials
→ Proceed to Unit 3