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Subelement E3
RADIO WAVE PROPAGATION
Section E3B
Transequatorial propagation; long path; gray-line; multi-path; ordinary and extraordinary waves; chordal hop, sporadic E mechanisms
What is transequatorial propagation?
  • Propagation between two mid-latitude points at approximately the same distance north and south of the magnetic equator
  • Propagation between any two points located on the magnetic equator
  • Propagation between two continents by way of ducts along the magnetic equator
  • Propagation between two stations at the same latitude

This propagation mode can provide contact from 28-432 MHz. It is thought to be due to irregularities in the F-Layer above the equator bending and reflecting the signals. (drichmond60)

Hint: The prefix trans- means across (or, in chemistry, on opposite sides).

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What is the approximate maximum range for signals using transequatorial propagation?
  • 1000 miles
  • 2500 miles
  • 5000 miles
  • 7500 miles

The transequitorial propagation (TEP) mode can provide contact from 28-432 MHz. It is thought to be due to irregularities in the F-Layer above the equator bending and reflecting the signals. The transmit and receive stations have to be approximately equidistant from and on opposite sides of the equator.

Memory tip: Stations have to be approximately the same distance from the equator, so the equator splits the total distance between them 50/50 (or 50%). Pick the answer that starts with 50 (5000 miles).

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What is the best time of day for transequatorial propagation?
  • Morning
  • Noon
  • Afternoon or early evening
  • Late at night

Afternoon and Evening Trans-equatorial Propagation are two distinctly different types of Trans-equatorial Propagation.

Afternoon Trans-equatorial Propagation peaks during the mid-afternoon and early evening hours and is generally limited to distances of 4,000–5,000 miles. Signals propagated by this mode are limited to approximately 60 MHz. Afternoon Trans-equatorial Propagation signals tend to have high signal strength and suffer moderate distortion due to multipath reflections.

Evening Trans-equatorial Propagation peaks in the evening around 1900 to 2300 hours local time. Signals are possible up to 220 MHz, and even very rarely on 432 MHz. Evening Trans-equatorial Propagation is quenched by moderate to severe geomagnetic disturbances. The occurrence of evening Trans-equatorial Propagation is more heavily dependent on high solar activity than is the afternoon type. = K4AGO www.wikipedia.org

Memory tip: Signal is crossing over the tropics. When's the best time to enjoy a tropical cocktail? Afternoon or early evening!

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What is meant by the terms extraordinary and ordinary waves?
  • Extraordinary waves describe rare long skip propagation compared to ordinary waves which travel shorter distances
  • Independent waves created in the ionosphere that are elliptically polarized
  • Long path and short path waves
  • Refracted rays and reflected waves

A radio wave entering an ionized region like the ionosphere in which there is also a magnetic field, will split into two waves which are elliptically polarized with their E field at right angles to each other. These are the extraordinary and ordinary waves that take a separate path to the receiver.

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Which amateur bands typically support long-path propagation?
  • 160 meters to 40 meters
  • 30 meters to 10 meters
  • 160 meters to 10 meters
  • 6 meters to 2 meters

If you're asking: "How typical is typical?" then you're overthinking it.

Without thinking about where we are in the sunspot cycle or what time of day or year it is, then which bands might potentially carry your signal the long way around the planet?

Any HF band or 160m might work.

It would be highly atypical for 6m or 2m to be open in such a way.

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Which of the following amateur bands most frequently provides long-path propagation?
  • 80 meters
  • 20 meters
  • 10 meters
  • 6 meters

Because DX working is relatively easy this band tends to be the most congested of the HF bands. Propagation is primarily via the F2 layer, which can remain intact for most of the 24-hour cycle under solar maximum conditions.

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Which of the following could account for hearing an echo on the received signal of a distant station?
  • High D layer absorption
  • Meteor scatter
  • Transmit frequency is higher than the MUF
  • Receipt of a signal by more than one path

Particularly when using HF there may be more than one propagation path that the signal can take to get from the distant station to your receiver. RF signals travel at the speed of light, but if the distance is great enough there can be an audible delay between the two signals.

Your receiver receives signals from both paths, thus causing the echo.

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What type of HF propagation is probably occurring if radio signals travel along the terminator between daylight and darkness?
  • Transequatorial
  • Sporadic-E
  • Long-path
  • Gray-line

Along the twilight region the absorption of signals by the D layer rapidly ceases while the E- and F-layers remain for a while with an MUF of up to 5MHz. This gives a region of enhanced 1.8MHz and 3.6MHz propagation called the Gray line, which forms an approximate great circle. For each station the time for the Gray line to pass by is in the order of minutes and the direction of enhanced propagation is along the Gray line, in other words approximately north and south. -ctrstocks

Hint: Think of the twilight region as the gray area between light and dark.

Hint2: Think White(light)+Black(Dark) colors when mixed produce "Gray"

-KE0IPR

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At what time of year is Sporadic E propagation most likely to occur?
  • Around the solstices, especially the summer solstice
  • Around the solstices, especially the winter solstice
  • Around the equinoxes, especially the spring equinox
  • Around the equinoxes, especially the fall equinox

Sporadic E displays seasonal patterns. Sporadic E activity peaks predictably in the summertime. In North America, the peak is most noticeable in mid-to-late June (e.g. near the summer solstice), trailing off through July and into August. A much smaller peak is seen around the winter solstice. https://en.wikipedia.org/wiki/Sporadic_E_propagation

-KE0IPR

Silly hint: when the kids are off from school, in summer, their schedule tends to be more -sporadic-

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What is the cause of gray-line propagation?
  • At midday, the Sun super heats the ionosphere causing increased refraction of radio waves
  • At twilight and sunrise, D-layer absorption is low while E-layer and F-layer propagation remains high
  • In darkness, solar absorption drops greatly while atmospheric ionization remains steady
  • At mid-afternoon, the Sun heats the ionosphere decreasing radio wave refraction and the MUF

Along the twilight region the absorption of signals by the D layer rapidly ceases while the E- and F-layers remain for a while with an MUF of up to 5MHz. This gives a region of enhanced 1.8MHz and 3.6MHz propagation called the Gray line, which forms an approximate great circle. For each station the time for the Gray line to pass by is in the order of minutes and the direction of enhanced propagation is along the Gray line, in other words approximately north and south.

ctrstocks

Hint: Think of Gray as Twilight time. Only one answer has Twilight in it.

-KE0IPR

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At what time of day is Sporadic-E propagation most likely to occur?
  • Around sunset
  • Around sunrise
  • Early evening
  • Any time

Not an explanation but a Helpful Mnemonic: It is precisely because this sort of propogation is sporadic is why it can occur at ANY time!! - KM4HOC

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What is the primary characteristic of chordal hop propagation?
  • Propagation away from the great circle bearing between stations
  • Successive ionospheric reflections without an intermediate reflection from the ground
  • Propagation across the geomagnetic equator
  • Signals reflected back toward the transmitting station

When a signal approaches the ionosphere at a steep angle the signal penetrates the ionosphere and may pass right through, or be 'reflected' back (green ray, right). It is actually refracted rather than reflected. However, when a signal approaches the ionosphere at a grazing angle, the likelihood of 'reflection' is higher than for vertically approaching signals. The penetration is less and the attenuation is less. Further, if the angle is low enough, the signal can be reflected again off the ionosphere without first hitting the ground (red ray, right).

This 'chordal hop' process is believed to be common at night when the F layer is stable. Because there is no ground reflection involved, and less penetration of the ionosphere, the attenuation is much less than with other propagation mechanisms, and as a result signals are stronger. In order to enhance the possibility of Chordal Hop, it is important to make use of antennas with the lowest possible beam elevation, to ensure that the signal hits the ionosphere as far from the transmitter as possible.

-d6epk

Hint: The correct answer is the only one that mentions the ground in it.

-KE0IPR

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Why is chordal hop propagation desirable?
  • The signal experiences less loss along the path compared to normal skip propagation
  • The MUF for chordal hop propagation is much lower than for normal skip propagation
  • Atmospheric noise is lower in the direction of chordal hop propagation
  • Signals travel faster along ionospheric chords

Here's a simple explanation with a picture:

http://www.qsl.net/sv1uy/chordal-hop.html

Normally, you'd expect HF radio waves to bounce between the Earth and the ionosphere, up and down, being partially absorbed, refracted, and diffused in every direction, which decreases received signal strength. Hopefully, enough is reflected that the transmitter can be heard.

With chordal hop propagation, some of the radio waves encounter the ionosphere at an angle where they are given a few chance to skip off of the ionosphere one or more times in a row without skipping off of the Earth, which decreases losses along that path.

Test Hint: There are no chords in the right answer. -KE0IPR

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What happens to linearly polarized radio waves that split into ordinary and extraordinary waves in the ionosphere?
  • They are bent toward the magnetic poles
  • Their polarization is randomly modified
  • They become elliptically polarized
  • They become phase-locked

The radio wave splits into two waves called the extraordinary wave and the ordinary wave when it enters the ionosphere.

The terms ordinary and extraordinary waves describe the independent waves created in the ionosphere that are elliptically polarized.

-KE0IPR

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