Question T9A09
From subelement T9 - T9A
What is the approximate length, in inches, of a half-wavelength 6 meter dipole antenna?
Why is this correct?
Answer C (112 inches) is correct. For 6 meters (50 MHz), a theoretical half-wavelength is 3 meters or about 118 inches. However, real antennas are approximately 5% shorter due to stray capacitance between the wire and nearby objects like ground and structures. So 118 inches × 0.95 = 112 inches. Option A (6 inches) confuses band name with length, B (50 inches) is roughly a quarter-wave, and D (236 inches) is about a full wavelength.
Memory tip
Remember the 5% shortening factor applies to all real-world dipoles—it's not just a 6-meter quirk. When you see wavelength calculations in amateur radio, always reduce the theoretical length by about 5% for practical antennas. This accounts for the antenna's interaction with its environment.
Learn more
The 6-meter band encompasses 50-54 MHz, making it popular for both local and long-distance communication through sporadic-E propagation. A 112-inch dipole (about 9.3 feet) is manageable for home installation compared to lower HF bands. Understanding antenna resonance and the relationship between physical length and electrical length helps when adjusting antenna systems for optimal emission standards compliance and efficient radiation patterns.
Think about it
Why do you think amateur antennas need to be shorter than the theoretical wavelength calculation, and how might this principle affect other antenna designs?