CA_BASIC

Basic - Antennas and feed lines

Antennas and feed lines follows the B-006 section of the Canadian question bank.

140

Questions

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Pool: Basic
Questions: 140
Topic: Antennas and feed lines
Region: CA

Review by section order to build the topic framework first.

For regulatory and safety questions, prefer compliant and conservative actions.

For calculations, check units, multipliers, and approximations.

Topic Study Guide

This topic covers section B-006 of the Canadian Basic exam, focusing on antenna principles, feedline types, impedance matching, and electromagnetic wave polarization. Mastering wavelength and frequency calculations, along with antenna radiation patterns, is key to passing this section.

High-Yield Checks

Wavelength & Antenna Length Formulas: Free space wavelength is calculated as 300/f (MHz). The practical physical length of a half-wave dipole is 143/f (MHz) in metres.
Feedline Characteristics: Coaxial cable is widely used due to its versatility and ease of routing. A solid shield offers the best shielding, and the velocity factor is primarily determined by the dielectric material.
Yagi Antenna Principles: Adding a longer element (reflector) directs radiation from the new element towards the dipole. The major advantage of increasing element spacing is higher gain.
Polarization & Radiation: Vertical polarization means electric lines of force are perpendicular to the Earth. A 1/4 wavelength vertical antenna on a car roof radiates equally well in all horizontal directions.

Trap Patterns

Confusing theoretical vs. practical length: When calculating a practical half-wave wire antenna, students often mistakenly use the theoretical 150/f formula instead of 143/f, which accounts for end effects.
Misunderstanding feedline loss: It is easy to mistakenly believe loss decreases at specific lengths or higher frequencies. In reality, signal loss always increases as length or operating frequency increases due to internal line losses.
Confusing Balun with Tuning stub: When connecting unbalanced coaxial cable to balanced window line, a balun is strictly required for the physical and electrical transition, not just a tuning stub.
Trap antenna misconceptions: Students often assume traps filter out harmonics. Because trap antennas resonate on multiple bands, they actually radiate harmonics more readily.

Review Steps

Step 1: Memorize core formulas. Practice calculating free-space wavelength (300/f) and practical half-wave dipole length (143/f), paying attention to units.
Step 2: Compare feedline types. Understand the physical differences, advantages, and disadvantages of coaxial cable, window line, and open-wire line.
Step 3: Build antenna radiation models. Draw or visualize the radiation patterns of dipoles, Yagis, and vertical antennas to grasp polarization and gain concepts.
Step 4: Understand impedance and SWR. Review how impedance mismatch causes modern transceivers to reduce power, and how radials reduce ground losses.

Quick Checks

Which constant should you use to calculate the practical length of a half-wave dipole for 28.150 MHz?
What happens to signal loss as the length of a transmission line is increased?
In a Yagi antenna, in what direction does the radiation strength increase when a longer element is added?
What does the 'i' stand for in the antenna gain unit dBi?

Questions in This Topic