Final Assessment — LOG PERIODIC ANTENNA — VHF

TM-ANT-043 — Open Handout Course: TM-ANT-043 Reference: TM-ANT-043 handout Questions: 15 Passing score: 13/15 (87%). All calculation questions (Q6–Q9) must be correct. Time limit: 20 minutes Notes: Closed handout. No references during the assessment.

Questions

Q1. What is the operating principle of the LOG PERIODIC ANTENNA — VHF? State it in one sentence using technical terms.

Q2. Log periodic dipole array with boom-fed transposed element feed; frequency-independent operation. Gain is achieved throu Explain the significance of this principle for antenna performance.

Q3. What determines the resonant frequency of the LOG PERIODIC ANTENNA — VHF? Name the primary physical parameter(s) and state whether increasing that parameter raises or lowers resonant frequency.

Q4. Chapter 3 specifies particular materials for the LOG PERIODIC ANTENNA — VHF. Name two materials where a substitution would change RF performance and explain the effect.

Q5. What is the first step of the Chapter 4 assembly procedure? Why must the steps be performed in the specified order?

Q6. [Calculation] Using the formula from Appendix A (λ = 300 / fMHz): Compute the element length for a frequency 10% higher than the design frequency. Show all work and state the result with units.

Q7. [Calculation] Using the formula: ΔL = −0.0085 × dboom × delem / λ² (approximate) Calculate a result for a specific antenna scenario. Show all work.

Q8. [Calculation] Your NanoVNA shows minimum SWR at 7.350 MHz. The design frequency is 7.150 MHz. Compute the percentage deviation and the required length correction. Show all work.

Q9. [Calculation] Compute the reflected power percentage for SWR = 2.5:1. Formula: RP(%) = ((SWR − 1)/(SWR + 1))² × 100. Show all work.

Q10. During Chapter 5 calibration, your SWR at the design frequency is 3.8:1. What does Chapter 6 direct you to do? What adjustment direction is required if resonance is above the design frequency?

Q11. What is the SWR acceptance criterion stated in Chapter 7 for the LOG PERIODIC ANTENNA — VHF? State it exactly: value and condition.

Q12. What is the difference between the Chapter 6 tuning procedure and the Chapter 7 verification procedure? Which permits adjustments?

Q13. During Chapter 7 verification, SWR measures 2.6:1. You re-trim the element and re-measure: SWR is now 1.7:1. Is the verification valid? What is the correct action?

Q14. List four required items in a verification log entry per Chapter 7.

Q15. After completing Chapter 7 verification with all checks passing, what can you conclude about the LOG PERIODIC ANTENNA — VHF? What can you NOT conclude?

— Turn page for answer key —

Answer Key

All answers directly verifiable from TM-ANT-043.

A1. See TM §2-1. The answer is the first substantive statement of Chapter 2. TM ref: §2-1

A2. See TM §2-1. The significance is stated in Chapter 2, usually in terms of bandwidth, efficiency, or pattern. TM ref: §2-1

A3. See Chapter 2. For wire antennas, physical length is primary. Loading elements (coils, capacitors) change effective electrical length. Longer = lower resonant frequency. TM ref: Ch. 2, App. A

A4. See Chapter 3. Critical materials include wire gauge (affects conductor loss), coax type (velocity factor changes matching section length), and ferrite type (affects impedance transformation at frequency). TM ref: Ch. 3

A5. See Chapter 4, step 1. The sequence exists because each step has physical or electrical dependencies on prior steps. TM ref: Ch. 4

A6. Formula: λ = 300 / fMHz. Frequency 10% higher = element 10% shorter. Confirm your result is physically plausible (shorter wire = higher frequency). TM ref: App. A

A7. Formula: ΔL = −0.0085 × dboom × delem / λ² (approximate). Show substitution, arithmetic, result with units. TM ref: App. A

A8. Deviation = (7.350 − 7.150) / 7.150 × 100 = 2.8% above design frequency. Antenna is electrically short. Required correction: lengthen element by approximately 2.8%. TM ref: App. A, Ch. 6

A9. RP(%) = ((2.5 − 1)/(2.5 + 1))² × 100 = (1.5/3.5)² × 100 = (0.4286)² × 100 = 18.4% reflected. TM ref: App. A

A10. See Chapter 6. High SWR at design frequency with resonance above → antenna is short → lengthen the radiating element. Chapter 6 specifies the trim procedure. TM ref: Ch. 6

A11. Criterion: 2.0:1 across 50–150 MHz | ____ |. Check your wording against Chapter 7 — numeric value and conditions must match exactly. TM ref: Ch. 7

A12. Tuning (Ch. 6) allows active adjustments to bring the antenna within specification. Verification (Ch. 7) confirms the result and allows no adjustments. Only tuning permits adjustments. TM ref: Ch. 6, Ch. 7

A13. No — the verification is invalid. Making adjustments during verification invalidates it. Correct action: return to Chapter 6 tuning with the current element length, complete tuning, then restart the full Chapter 7 verification with no further adjustments. TM ref: Ch. 7

A14. See Chapter 7, final steps. Required items typically include: date, antenna type, operating frequency, height/orientation, SWR measurement, pass/fail determination, operator name. TM ref: Ch. 7

A15. You CAN conclude: the antenna meets the specified SWR and resonance criteria at this time, at this location and height, in this orientation. You CANNOT conclude: performance will be identical at a different site, height, or orientation; or that the antenna will remain in spec without re-verification. TM ref: Ch. 7

Score Routing

Question → Unit map: Q1–Q3 → Unit 1 (Theory); Q4–Q5 → Units 2–3 (Materials/Assembly); Q6–Q9 → Unit 4 (Calculations); Q10 → Unit 4; Q11–Q15 → Unit 5 (Verification).