The Basic lessons · Feedlines and antenna systems · B-006-010

Building and Tuning Vertical Antennas

Learn how to calculate the physical length of vertical antennas for different frequencies and understand why specific designs improve performance. This lesson explains how to match antennas to your radio using radials and loading coils.

This lesson is part of SignalPrep Pro. The subsection's 11 exam questions are free to practise: practise B-006-010.

What this subsection asks

• How do you calculate the approximate length in metres of a quarter-wavelength antenna for use on frequencies below 30 MHz?
• If you made a quarter-wavelength vertical antenna for 21.125 MHz, approximately how long would it be?
• If you made a half-wavelength vertical antenna for 223 MHz, approximately how long would it be?
• Why is a five-eighths wavelength vertical antenna better than a quarter-wavelength vertical antenna for VHF or UHF mobile operations?
• If a quarter-wavelength vertical antenna is placed on the roof of a car, in what direction does it send out radio energy?
• What is an advantage of downward sloping radials on a ground plane antenna?
• What configuration of radials will match an elevated quarter-wave vertical antenna to a 50-ohm coaxial cable?
• Which of the following transmission lines will give the best match to the base of a quarter-wave ground-plane antenna?
• How can a vertical antenna, 2 metres in length, be made to resonate in the 80-metre band for mobile use?
• Why is a loading coil often used with an HF mobile vertical antenna?
• When using a ground mounted vertical HF antenna, what can you do to reduce ground losses?