There are many interesting types of propagation that occur on the HF bands. They include transequatorial propagation, long-path propagation, and gray-line propagation.
Transequatorial propagation is propagation between two mid-latitude points at approximately the same distance north and south of the magnetic equator. The approximate maximum range for signals using transequatorial propagation is 5000 miles, and the best time of day for transequatorial propagation is afternoon or early evening.
QUESTION: What is transequatorial propagation? (E3B01)
ANSWER: Propagation between two mid-latitude points at approximately the same distance north and south of the magnetic equator
QUESTION: What is the approximate maximum range for signals using transequatorial propagation? (E3B02)
ANSWER: 5000 miles
QUESTION: What is the best time of day for transequatorial propagation? (E3B03)
ANSWER: Afternoon or early evening
Long-path propagation is the type of propagation that occurs when the longer of the two direct paths between stations is better for communications than the shorter path. 160 to 10 meters are the amateur bands that typically support long-path propagation. Although 20 meters is the amateur band that most frequently provides long-path propagation, long-path propagation can occur on any band, 160 meters through 10 meters.
QUESTION: Which of the following amateur bands most frequently provides long-path propagation? (E3B06)
ANSWER: 20 meters
QUESTION: Which amateur bands typically support long-path propagation? (E3B05)
ANSWER: 160 meters to 10 meters
Sporadic-E propagation occurs when unusually dense patches of ionization form in the E layer of the ionosphere. Sporadic E propagation can occur at any time of day, and is most likely to occur is around the solstices, especially the summer solstice.
QUESTION: At what time of day can sporadic E propagation occur? (E3B11)
ANSWER: Any time
QUESTION: At what time of year is sporadic E propagation most likely to occur? (E3B09)
ANSWER: Around the solstices, especially the summer solstice
Chordal hop propagation occurs when a radio wave is refracted by the ionosphere such that the refracted wave hits the ionosphere and is refracted a second or third time before hitting the ground. Chordal hop propagation is more desirable than multi-hop propagation that uses the Earth as a reflector because chordal reflections are less lossy than Earth reflections.
QUESTION: What is the primary characteristic of chordal hop propagation? (E3B12)
ANSWER: Successive ionospheric refractions without an intermediate reflection from the ground
QUESTION: Why is chordal hop propagation desirable? (E3B10)
ANSWER: The signal experiences less loss compared to multi-hop using Earth as a reflector
When a linearly-polarized radio wave enters the ionosphere, it splits into two independent waves, called the ordinary wave and the extraordinary wave, each having slightly different propagation characteristics. When these two waves reemerge from the ionosphere, instead of being linearly polarized like the radio wave that entered the ionosphere, the ordinary and extraordinary waves are now elliptically polarized.
QUESTION: What happens to linearly polarized radio waves that split into ordinary and extraordinary waves in the ionosphere? (E3B07)
ANSWER: They become elliptically polarized
QUESTION: What is meant by the terms “extraordinary” and “ordinary” waves? (E3B04)
ANSWER: Independent waves created in the ionosphere that are elliptically polarized