Question T3C03
From subelement T3 - T3C
What is a characteristic of VHF signals received via auroral backscatter?
Why is this correct?
Auroral backscatter signals are distorted and have highly variable signal strength because the aurora itself is constantly changing and shimmering. Unlike stable propagation modes, the aurora acts like a moving, reflective curtain that causes unpredictable signal variations. The other options are incorrect: auroral contacts aren't typically from 10,000+ miles, they can occur year-round during aurora activity (not just winter nights), and antenna direction depends on aurora location, not a fixed westward orientation.
Memory tip
Remember that atmospheric propagation modes reflect the stability of their reflecting medium. Stable reflectors (like steady ionospheric layers) give consistent signals, while dynamic reflectors (like the constantly shifting aurora) create unstable, varying signals. This principle applies across different propagation phenomena.
Learn more
Auroral backscatter involves bouncing signals off the aurora borealis or aurora australis, which appear as shifting curtains of light in polar regions. The aurora's electromagnetic properties fluctuate rapidly due to solar particle interactions with Earth's magnetosphere. This creates a constantly changing reflective surface, making auroral communication challenging but fascinating. Operators often use digital modes like MSK144 to handle the rapid signal variations and brief contact windows during auroral events.
Think about it
Why do you think digital modes like MSK144 work better than traditional voice modes for auroral communication, given what you now know about signal distortion and variability?