Ham Radio General Class Practice Test

How might a sky-wave signal sound if it arrives at your receiver by both short path and long path propagation?

1. Periodic fading approximately every 10 seconds

2. Signal strength increased by 3 dB

3. The signal might be cancelled causing severe attenuation

4. A well-defined echo might be heard

The correct answer is: A well-defined echo might be heard

When a sky-wave signal reaches a receiver through both short path and long path propagation, the phenomenon of multipath interference can occur. Each path the signal takes can result in slight differences in delay due to the varying distances involved. Because the short path and long path signals arrive at different times, they can constructively or destructively interfere with one another. A well-defined echo might be heard because the two signals are essentially the same signal transmitted back to the Earth from the ionosphere, but separated by additional travel time. This time difference may be perceptible as an echo, creating an audio artifact that can be recognized by the operator as a distinct repeat of the original transmission. This is especially noticeable in conditions where both paths are equally strong and closely aligned in frequency. On the other hand, periodic fading or severe attenuation are more related to other forms of interference or environmental conditions rather than specifically the combination of short and long path signals. An increase in signal strength would not typically manifest as a notable change in received audio but rather in clarity and volume, and would not explain the observable echo. Hence, hearing a well-defined echo is the most characteristic outcome of receiving signals via both propagation paths simultaneously.