|What is the cause of auroral activity?|
|A. The interaction in the F2 layer between the solar wind and the Van Allen belt|
|B. A low sunspot level combined with tropospheric ducting|
|C. The interaction in the E layer of charged particles from the Sun with the Earth’s magnetic field|
|D. Meteor showers concentrated in the extreme northern and southern latitudes|
E3: RADIO WAVE PROPAGATION
E3A - Electromagnetic waves; Earth-Moon-Earth communications; meteor scatter; microwave tropospheric and scatter propagation; aurora propagation
An electromagnetic wave is a wave consisting of an electric field and a magnetic field oscillating at right angles to each other. (E3A15) Electromagnetic waves travel in free space because changing electric and magnetic fields propagate the energy. (E3A16)
An important characteristic of an electromagnetic wave is its polarization. A wave is said to be vertically polarized if its electric field is perpendicular to the Earth and horizontally polarized if the electric field is parallel to the Earth. Waves with a rotating electric field are circularly polarized electromagnetic waves. (E3A17)
Moon bounce, or Earth-Moon-Earth (EME) communication
One of the more exotic amateur radio activities is earth-moon-earth (EME) communication, sometimes called “moon bounce.” As this name implies, radio amateurs actually bounce their signals off the moon.
This is the ultimate DX. The approximate maximum separation measured along the surface of the Earth between two stations communicating by Moon bounce is 12,000 miles, if the Moon is visible by both. (E3A01)
Because the signal travels such a long way, you need to do everything you can to avoid signal loss. So, for example, scheduling EME contacts when the Moon is at perigee will generally result in the least path loss. (E3A03) Perigee is the point at which the Moon is the closest to Earth.
One interesting phenomenon is libration fading. Libration fading of an Earth-Moon-Earth signal is a
fluttery, irregular fading. (E3A02) This fading is caused by the irregular surface of the Moon, and the peaks can last for up to two seconds on the 2m band. These peaks can actually help operators make contacts when they would otherwise be impossible.
Some amateur radio operators bounce their signals off meteor trails. This type of propagation is called meteor scatter. Meteor scatter propagation is possible because when a meteor strikes the Earth's atmosphere, a cylindrical region of free electrons is formed at the E layer of the ionosphere. (E3A08) 28 - 148 MHz is the frequency range that is well suited for meteor-scatter communications. (E3A09)
Microwave tropospheric and scatter propagation
While HF propagation is not affected by weather conditions, the same cannot be said for microwave propagation. Temperature inversion is the type of atmospheric structure can create a path for microwave propagation. (E3A10) These paths form in the troposphere and and are often called tropospheric ducts.
Tropospheric propagation of microwave signals often occurs along warm and cold fronts. (E3A05)
And, atmospheric ducts capable of propagating microwave signals often form over bodies of water.
(E3A07) The typical range for tropospheric propagation of microwave signals is 1200 miles. (E3A11)
Tropospheric propagation is quite predictable. There are even websites that you can visit that will tell you where tropospheric ducts currently exist. These websites include William Hepburn's Radio & TV
DX Information Centre (http://www.dxinfocentre.com/tropo.html). This site shows where ducting is occurring on Hepburn maps, which are maps that predict the probability of tropospheric propagation. (E3A04)
Rain can also affect the propagation of microwave signals. The rain must be within radio range of both stations for microwave propagation via rain scatter. (E3A06)
Another interesting type of propagation is aurora propagation. The cause of auroral activity—sometimes called the Northern Lights—is the interaction in the E layer of charged particles from the Sun with the Earth's magnetic field. (E3A12)
From the contiguous 48 states, North is the approximate direction an antenna should be pointed to take maximum advantage of aurora propagation. (E3A14) CW is the emission mode that is best for aurora propagation. (E3A13)
Thanks to KB6NU DAN ROMANCHIK