Transequatorial propagation (TEP) is a mode of radio wave propagation that occurs when signals travel over long distances by reflecting off the ionosphere near the equator. This allows communication between points on opposite sides of the equator.

TEP typically occurs over distances of 2,000 to 3,000 miles because that distance is the typical "skip zone", or the area under the path the signal takes to the ionosphere and back.

The propagation path is usually perpendicular to the geomagnetic equator. This alignment with the geomagnetic equator maximizes the ionospheric reflection, enabling effective long-distance communication.

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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).

Memory tip: Remember the song "I will walk 500 miles and I will walk 500 more." Multiply by 10, and If you know that 80s song you will remember this answer of 5000.

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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. 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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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 may take separate paths to the receiver.

The ordinary wave, or o-wave has an electrical field oriented parallel to the Earth's magnetic field. The extraordinary wave, or x-wave has an electrical field oriented perpendicular to the Earth's magnetic field. The waves also travel at different speeds, creating a phase difference between them. Above 10 MHz, the two waves travel nearly identical paths. At 7 MHz and below, the two waves can travel different paths and in different directions.

Hint: "Extraordinary" and "Elliptical" both start with the letter E

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Long-distance propagation on longer wavelengths such as the 160-meter band is most effective when the path is entirely in darkness.

This is because, during the night, the ionosphere's D-layer dissipates. The D-layer of the ionosphere absorbs RF on lower frequency (longer wavelength) bands, including the 30m, 40m, 60m, 75-80m, and 160 meter bands.

With the D-layer gone, radio waves can more easily reflect off the higher F-layer, allowing for greater distances. In contrast, during daylight, the D-layer is present and significantly absorbs signals on the 160-meter band, reducing the effective communication range.

Thus, a path entirely in darkness provides the best conditions for long-distance propagation on 160 meters.

A mnemonic for this can be Long waves for Long winter nights.

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Because DX working is relatively easy on the 20 meter band, it 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.

Hint: for 2 of us to play long distance =20meter

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Radio waves are electromagnetic waves that travel in a straight line forever much like light, unless they are refracted. In the case of RF, that refraction is provided by the ionosphere.

If you imagine the ionosphere as a giant mirror around the earth and you point a laser straight up, then you expect the returned beam to come straight back down to you. If you then move the laser a little to the side the returned beam will be a little ways away from you. As you move the beam further away from straight up, the returned beam moves further and further away from you. Eventually your angle will be very low and the lower you get it the further it will go. The same principle applies for skywave propagation. Therefore lowering a signals transmitted elevation angle will increase the hop distance.

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Ground waves are waves emitted at less than a wavelength above the ground that travel in contact with the surface of the earth. At higher frequencies like most of HF and above this is especially bad; the waves are severely attenuated and nothing amazingly good happens.

At 160m and below frequencies with vertical polarization though they may be able to travel a few hundred miles since they can get refracted in such a way as to follow the curve of the earth without too much attenuation, whereas at 10m they tend to die out in 10 miles or less. Note that this requires vertical polarization; horizontal waves will short circuit immediately since the whole electrical field tends to end up in the somewhat conductive ground.

How well surface wave propagation works depends on the conductivity of the soil or water that makes up the earth's surface on the path.

Ground wave propagation is most useful on the 1.8MHz and 3.5MHz bands during daytime.

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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

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

Alternative silly hint: Sporadic and summer solstice are alliterative.

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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.

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Sporadic E propagation occurs during the day, since it's a higher frequency propagation.

It uses the higher frequencies, in the VHF. You reflect your signals off of the very low layers of the ionosphere, which absorb low frequencies, but reflect higher frequency.

You can get more detail from the Wiki page, Spordiac E Wiki

Memory Aid: One of these things is not like the other. All incorrect choices describe night/evening conditions, while the correct one is the only one that describes daytime.

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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.

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

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Ground waves are a result of interaction of the radio signal with the ground. The interaction has the effect of causing the signal to follow the curvature of the earth. Ground wave propagation is most useful on the 1.8 MHz and 3.5 MHz bands during daytime.

This only works with vertical waves; horizontal waves will short circuit immediately since the whole electrical field tends to end up in the somewhat conductive ground.

One way to remember this answer is to consider commercial AM broadcast: ground-wave propagation via vertical towers that polarize vertically.

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