The approximate maximum separation along the surface of the Earth between two stations communicating by moonbounce is 12,000 miles, as long as both can “see” the moon. Libration fading of an earth-moon-earth signal is characterized by a fluttery irregular fading. When scheduling EME contacts, the least path loss is when the moon is at perigee. The type of receiving system desirable for EME communications is equipment with very low noise figures. Transmit and receive time sequencing is normally used on 144 MHz when attempting an EME contact. Two-minute sequences are used, where one station transmits for a full two minutes and then receives for the following two minutes. The time sequences normally used on 432 MHz are two-and-one-half minute sequences, where one station transmits for a full 2.5 minutes and then receives for the following 2.5 minutes. The frequency range you would normally tune to find EME stations in the 2 meter band is 144.000 - 144.100 MHz. On the 70 cm band it is 432.000 - 432.100 MHz. When a meteor strikes the Earth's atmosphere, a cylindrical region of free electrons is formed at the E layer of the ionosphere. The range of frequencies well suited for meteor-scatter communications is 28 - 148 MHz. When attempting a meteor-scatter contact on 144 MHz, the transmit and receive time sequences normally used are 15-second sequences, where one station transmits for 15 seconds and then receives for the following 15 seconds. Transequatorial propagation is propagation between two 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. The best time of day for transequatorial propagation is Afternoon or early evening. If an HF beam antenna must be pointed in a direction 180 degrees away from a station to receive the strongest signals the type of propagation probably occurring is Long-path. The amateur bands that typically support long-path propagation are 160 to 10 meters. The amateur band that most frequently provides long-path propagation 20 meters. Hearing an echo on the received signal of a distant station could be accounted by the receipt of a signal by more than one path. If radio signals travel along the terminator between daylight and darkness, the type of propagation probably occurring is Gray-line propagation. Gray-line propagation is most prevalent at sunrise and sunset. Gray-line propagation occurs because at twilight, solar absorption drops greatly, while atmospheric ionization is not weakened enough to reduce the MUF. During gray-line propagation contacts up to 8,000 to 10,000 miles on three or four HF bands. Auroral activity effects radio communications. It occurs in the ionosphere at E-region height. CW is the best emission mode for auroral propagation. CW signals have a fluttery tone. The cause of auroral activity is the emission of charged particles from the sun. From the contiguous 48 states, an antenna should be pointed North to take maximum advantage of auroral propagation. Selective fading is caused by phase differences in the received signal caused by different paths. The radio-path horizon distance exceeds the geometric horizon because radio waves may be bent. The VHF/UHF radio-path horizon distance exceeds the geometric horizon by approximately 15% of the distance. The radiation pattern of a 3-element, horizontally polarized beam antenna varies with height above ground. The main lobe takeoff angle decreases with increasing height. When mounted on the side of a hill, a horizontally polarized antenna's main lobe takeoff angle decreases in the downhill direction. The takeoff angle is lower compared with the same antenna mounted on flat ground. As the frequency of a signal is increased, its ground wave propagation decreases. Most ground-wave propagation has vertical polarization. The name of the high-angle wave in HF propagation that travels for some distance within the F2 region is the Pedersen ray. Tropospheric ducting is usually responsible for propagating a VHF signal over 500 miles. |