Unit 4 — Calibration and Tuning

TM-ANT-001 — Open Handout TM Chapters: Chapter 5, Chapter 6, Appendix A ELOs: Calibrate the DIPOLE CALIBRATION (HOMEBREW) to resonance; tune SWR to within acceptance criteria; apply frequency calculations Estimated time: 45 minutes (actual lab work required)

Step 1: Read the TM

Open TM-ANT-001. Read Chapter 5 — Calibration Procedure, Chapter 6 — Tuning and Adjustment, and Appendix A completely.

Then come back here.

Chapter 5 — Calibration Procedure

  1. Use a stable reference signal (WWV, beacon, or known local carrier).
  2. Measure resonance, SWR, or gain pattern.
  3. Compare against expected values from calculations.
  4. Apply corrections or document offsets.

Chapter 6 — Tuning and Adjustment

  1. Sweep across the target band.
  2. Shorten or lengthen elements in small steps.
  3. Record resonance shift per adjustment.
  4. Lock the final configuration.

Appendix A — Calculations and Formulas

No content extracted.

Key Formulas Summary

(See Appendix A in the TM)

Calibration vs. Tuning — Distinction

Calibration (Chapter 5): initial setup measurements to establish current antenna state — resonant frequency, SWR at design frequency, impedance at feedpoint. No adjustments yet; you are characterizing what you built.

Tuning (Chapter 6): active adjustments based on calibration data. Trim the element, adjust the matching network, or change height/orientation until Chapter 7 acceptance criteria are met.

Acceptance Criterion

Locate the SWR or resonance acceptance criterion in Chapter 5.

Write the exact criterion from the TM here before you start:

Lab Checklist

  • [ ] Antenna assembled per Chapter 4 and installed at operating height
  • [ ] NanoVNA or SWR bridge connected per Chapter 5
  • [ ] Chapter 5 calibration measurements taken and recorded
  • [ ] Resonant frequency identified (minimum SWR point)
  • [ ] SWR at design frequency recorded
  • [ ] Chapter 6 tuning performed if needed
  • [ ] Acceptance criterion met

Calibration Log

Parameter Measured Specification Pass/Fail
Resonant frequency (MHz) (design freq ± tolerance)
SWR at design frequency (from Ch. 5)
Feedpoint impedance (Ω) (from Ch. 2)

Practice Problems

P4-1. The design frequency of the DIPOLE CALIBRATION (HOMEBREW) is stated in Chapter 1. Using the formula from Appendix A, compute the theoretical element length for that frequency. Show all work.

P4-2. Your NanoVNA shows minimum SWR at a frequency 3% above the design frequency. Which direction do you adjust — lengthen or shorten? By what percentage?

P4-3. SWR at resonance is 1.8:1, but the acceptance criterion is SWR ≤ 2.0:1. Does the antenna pass? What does SWR 1.8:1 mean in terms of reflected power?

P4-4. Compute reflected power percentage for SWR = 2.0:1. Formula: reflected power (%) = ((SWR − 1)/(SWR + 1))² × 100

Answer Key — Practice Problems

P4-1. See Appendix A. For a dipole: L(ft) = 468/f(MHz). For a quarter-wave vertical: L(ft) = 234/f(MHz). Apply the formula specific to this antenna type.

P4-2. Resonance is above design frequency → antenna is electrically short → lengthen the element. Adjustment magnitude: approx. 3% longer.

P4-3. SWR 1.8:1 passes the 2.0:1 criterion. Reflected power: ((1.8−1)/(1.8+1))² × 100 = (0.8/2.8)² × 100 = 8.2% reflected.

P4-4. SWR 2.0:1: ((2−1)/(2+1))² × 100 = (1/3)² × 100 = 11.1% reflected. Most of the power still gets through.

Checkpoint

Before proceeding: - [ ] Calibration measurements taken and logged - [ ] Antenna tuned to within the acceptance criterion - [ ] You can compute element length adjustment from frequency error

→ Proceed to Unit 5