Practical takeaway
How radio signals travel, fading, multipath, polarization, absorption, and antenna orientation.
T3A · 12 pool questions
Signal Paths, Fading & Polarization
How radio signals travel, fading, multipath, polarization, absorption, and antenna orientation.
Technician exam focus
This group contains 12 questions in the current pool. The teaching below keeps the important tested terms visible while explaining what they mean in normal Amateur Radio use.
1. One signal can arrive by several paths
A VHF signal may reach you directly and after reflecting from buildings, terrain, or other surfaces. Those copies can add or cancel. That is multipath propagation, and it explains why moving an antenna only a few feet can change a signal dramatically. Rapid flutter heard while moving is often called picket fencing.
2. Polarization comes from antenna orientation
A vertically mounted antenna normally launches and receives vertically polarized waves; a horizontal antenna does the same for horizontal polarization. A strong polarization mismatch can reduce received strength. After ionospheric propagation, polarization can become elliptical, so either horizontal or vertical antennas may still receive part of the signal.
3. Fading has a physical cause
Irregular fading often comes from signals arriving over different paths and combining. The same multipath effect can increase errors in digital transmissions because delayed copies distort the waveform.
4. Rain matters more as frequency rises
Fog and light rain have little effect on 10-meter and 6-meter signals, but precipitation can significantly reduce range at microwave frequencies. Water absorption and scattering increase as frequency gets high enough.
T3A checklist
- Multipath can reinforce or cancel a received signal.
- Rapid mobile flutter from multipath is picket fencing.
- Antenna orientation determines the usual polarization of the transmitted wave.
- Multipath can increase digital-data error rates.
- The ionosphere can return HF signals to Earth.
- Fog/light rain have little effect on 10 m and 6 m; precipitation matters more at microwave frequencies.
Exam scope: NCVEC 2026–2030 Technician Class (Element 2), effective July 1, 2026 through June 30, 2030, with February 19, 2026 errata. The current NCVEC pool is the exam authority; explanatory prose here is SPARKA teaching material. NCVEC pool