Unit 3 — Assembly Procedures

TM-ANT-021 — Open Handout TM Chapter: Chapter 4 ELOs: Execute assembly in the correct sequence; achieve the physical dimensions specified Estimated time: 25 minutes

Step 1: Read the TM

Open TM-ANT-021. Read Chapter 4 — Assembly Procedures completely.

Then come back here.

Chapter 4 Content

CAUTION — RF EXPOSURE: Maintain minimum safe distance from all energized antenna elements during transmission. At QRP power levels (≤5 W) the MPE boundary is typically

  1. Wind matching transformer per design (49:1 unun: 3 trifilar turns primary on BN-43-2402 binocular core, or 2 turns primary and 14 turns secondary on FT-140-43 single core).
  2. Seal transformer in weatherproof enclosure. Route wire terminal out one end, coax SO-239 on side.
  3. Attach antenna wire to transformer wire terminal. Cut wire 5% long for trimming.
  4. Attach counterpoise wire (0.05λ minimum) to transformer ground/coax-braid terminal. Tape counterpoise away from antenna wire.
  5. Deploy antenna wire: raise far end as high as possible, at least 20 ft for HF operation. Attach end insulator and support halyard.
  6. Run coax from SO-239 to station. Install common-mode choke (Mix-31 toroid, 8 turns) at shack entry.
  7. Perform SWR sweep per Chapter 5.

Assembly Quality

Chapter 4 specifies 7 assembly steps.

Physical dimensions and assembly quality directly determine resonant frequency and feedpoint impedance: - Antenna length errors shift resonance: ~1% length error ≈ ~1% frequency shift at HF - Poor solder joints at the feedpoint create resistance that raises SWR and wastes power - Loose connections in a matching network change the impedance transformation ratio - Incorrect element spacing in a beam changes gain and front-to-back ratio - Coax shield continuity to the feedpoint determines how much common-mode current flows on the shield

If Chapter 4 specifies a pre-installation check (e.g., ohmmeter continuity or pre-resonance trim), do it. These checks catch fabrication errors before the antenna is in the air.

Self-Check Questions

SC3-1. How many assembly steps does Chapter 4 specify?

SC3-2. What is the specified length of the main radiating element? How was that length calculated?

SC3-3. Does Chapter 4 specify a feedpoint connection method? What is the correct solder or mechanical technique?

SC3-4. Does Chapter 4 require a pre-installation check? What does it verify?

SC3-5. If the assembled element is 2% shorter than specified, which direction will resonance shift? By approximately how much?

Answer Key

SC3-1. Count the numbered steps in Chapter 4.

SC3-2. See Chapter 4. The design length comes from the formula in Appendix A (typically 468/f or 234/f in feet, adjusted for wire diameter and proximity effects).

SC3-3. See Chapter 4. Good RF solder joints are smooth, shiny, and mechanically sound. Cold joints show up as dull, granular surfaces.

SC3-4. Scan Chapter 4 for verification steps before installation. Common pre-checks: DC continuity across element, coax shield-to-ground, open circuit across element center.

SC3-5. Shorter element = higher resonant frequency. At HF, the shift is approximately proportional: 2% shorter ≈ 2% higher frequency.

Checkpoint

Before proceeding: - [ ] You have read Chapter 4 completely - [ ] You can state the specified element length and its derivation - [ ] You have assembled the antenna per Chapter 4

→ Proceed to Unit 4