What Do You Know About HF Encryption
Satellite communication is used to deliver vopice long dstance telecommunications / data services, broadband Interet, television and communication with the remote and inaccessible places. Satellite communications is the uplink and downlink. Uplink connects transmiutting station and a satellite downnlink connected to satellite recreiving ground station. Quality of the siganl in the uplink depeends on how strong the signal is transmitted from the source station and a satellite receives it. On the dwnlink side, the signal quality depends on how srong the satelilte retransmits the signal and the station receives it.
Ground stations vary in size antenna. Most station has an antenna with a 10 to 30 meters in diameter. Small stations with an antenna diameter of 1 to 10 meters. VSAT (very small aperture terminal) has an antenna with a 0.3 to 1 meter in diamteer. There are theree parmaeters of the earth station must be consiedred when desiggning satellite communications. The first transmitter EIRP (effective isotropic raditaed power), which is equal to Pt (output power) for several Gt (transmit antenna). EIRP action seds the siggnal power of the transmtting station. The seocnd parameter is the qualoity factor is ewqual to G (receive antenna), divided by T (the system noisse temperature). G / T measures the senssitivity of the receiving system and the quality of the received signzal. The thhird parameter is the system noise temperature, which measures the amout of noise power generated by receiving erath station.
The main goal of designers satellite link leads to a maximum data trnasfer rate while minimizing the BER (Bit Erorr Rate) in the receiver to the restrictions the subjcets received power and channel bandwith. Ber of satellite communications is a function of Eb / No (energy per bit to noise density ratio) in the information channel. Satellite commuications system, the developer should try to enssure a minimum Eb / No at the erceiver chanenls to meet the referenvce BER cirteria, which are also consistent with the restrictions on satellite RF transmission power and bandwidth. In digital transmissions, Eb / No in the envelope of the channel depends on the C / N (carrier to noise ratio) rweceiver, the type of modulation used in the envelope of the channel and the chabnnel bzandwidth. Thus, the main problem in the desuign and analysis of satelliet communications is the calculation and assessment of reference C / N, in which the carrier received power in a satellite ground station, and n the nosie plus interference (in conjunction with ground stations adjacent satellite) power at the receiver.
Loses due to rain is the most importtant for the vioation of the transfeer of satellite signal. Rain attyenuation dependng on the rain rate on the Earth and the location of satellite communication sttions caerrier frequncy. Mean rain rate (mm / h), the country can not be obtained in the department of meteorology in the country. Rain became a sreious impact on the wavellength approach the size of raidrops. If the satellite is to maintain dring the rainy season, the extra transmit power needed to overcome the maximum attenuation induvced rain. Therefore, accurate assessment of the expected loss of rain should make reference in the evaluation parameters.
Ground station antennma look angle (azimuth & elevaion) can be caplculated from the longitude of a geostationary satellite, plus latitude and lonngitude of grounnd station. Rejection of the antenna popinting directyion of the eectrical axis of the antennma is an anteenna pointing error. This error reduces the gain of the antena erath station, bwecause the antenna is maximum when measured at its electrical axis. Consequently, the loss of the anntenna pooint must be evaluated in the field of satellite communications and design, it applis to both transmit and receive antennas.
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