Unit 2 — Construction and Materials
TM-GEAR-003 — Open Handout TM Chapter: Chapter 3 ELOs: Identify required components and materials; understand component selection criteria Estimated time: 20 minutes
Step 1: Read the TM
Open TM-GEAR-003. Read Chapter 3 — Equipment and Materials completely.
Then come back here.
Chapter 3 Content
| Design | Core | Wire | Turns | Freq range |
|---|---|---|---|---|
| 1:1 current (choke) | FT-240-31 | RG-303 coax, 12 passes | 12 | 1.8–30 MHz |
| 4:1 Guanella | 2× FT-140-43 | #16 bifilar, 8 turns | 8 | 1.8–30 MHz |
| 6:1 trifilar | FT-140-43 | #18 trifilar, 10 turns | 10 | 3.5–30 MHz |
| 9:1 trifilar | FT-240-43 | #16 trifilar, 9 turns | 9 | 1.8–30 MHz |
| 1:1 VHF/UHF air-core | None (air core) | RG-58 coax, 6 turns | 6 | 50–450 MHz |
Component Selection
Review the equipment and materials list in Chapter 3 carefully.
Before building, verify every item on the materials list. Key considerations: - Use the specified component types — substitutions may affect performance or frequency coverage - Non-inductive components are required in RF circuits; standard wirewound resistors are unsuitable - Toroids and ferrite cores are frequency-specific; use the specified core material (#43, #61, #67, etc.) - Connector types affect impedance — match the specified connector to avoid SWR errors - Wire gauge and insulation type affect current capacity and voltage breakdown
The quality of your materials sets the ceiling on the component's performance.
Self-Check Questions
SC2-1. List the three most critical components or materials specified in Chapter 3. Why are they critical?
SC2-2. Does Chapter 3 specify non-inductive resistors? If so, where are they used and why does it matter?
SC2-3. What connector type(s) does Chapter 3 specify, and what is the frequency/power justification?
SC2-4. Does Chapter 3 specify a particular ferrite core material or type? What is its significance?
SC2-5. What would be the consequence of substituting a standard wirewound resistor for a non-inductive type in an RF application?
Answer Key
SC2-1. See Chapter 3. Identify items with specific part numbers, special materials, or critical tolerances — these are the ones that most affect performance.
SC2-2. See Chapter 3. Non-inductive types are used wherever standard inductive wirewound resistors would add series inductance that degrades high-frequency performance.
SC2-3. See Chapter 3. SO-239, N-type, BNC, and SMA each have different frequency and power ratings.
SC2-4. See Chapter 3. Ferrite #43 is for 1–100 MHz; #61 for 10–200 MHz; #67 for 50–500 MHz. Wrong material = wrong permeability = wrong coupling or suppression.
SC2-5. A wirewound resistor has several microhenries of series inductance. At HF and VHF, this adds inductive reactance proportional to frequency, destroying the resistor's value as a termination or load.
Checkpoint
Before proceeding: - [ ] You have read Chapter 3 completely - [ ] You can name the critical components from memory - [ ] You understand why non-inductive and correct ferrite materials are required
→ Proceed to Unit 3