Unit 2 — Materials and Construction
TM-ANT-047 — 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-047. Read Chapter 3 — Materials and Construction completely.
Then come back here.
Chapter 3 Content
3-1. BILL OF MATERIALS
| Qty | Item | Specification |
|---|---|---|
| Per design | Copper wire (antenna elements) | #14 AWG solid or stranded copper, PVC-jacketed preferred for weather resistance |
| 1 | Feed-point insulator / center connector | SO-239 or UHF-F, weatherproof, UV-resistant housing |
| 2 | End insulators | Egg insulators or equivalent; rated for wire tension at operating temperature |
| As needed | Halyard / support rope | Dacron or polypropylene, non-conductive, UV-resistant |
| 1 | Choke balun (1:1 current balun) | Mix-31 ferrite cores, 8–12 turns of RG-142 or RG-8X through core; FB-31-6873 or equivalent |
| 1 | Coaxial feed line | RG-8X or RG-213 to station; minimize length for efficiency |
3-2. DIMENSION FORMULAS
Half-wave dipole element length (each arm, feet)
Larm = 234 / fMHz
Full dipole length (feet)
Ltotal = 468 / fMHz
Example: 40M at 7.150 MHz
Larm = 234 / 7.150 = 32.7 ft — each arm
Note: The 468 constant assumes wire of #12–#14 AWG copper at ambient temperature; adjust down 1–2% for thick conductors or cage construction (velocity factor <1).
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