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Due to the high orbital speed of the amateur satellites, the uplink and downlink frequencies will vary during the course of a satellite pass. This phenomenon is known as the Doppler effect . While the satellite is moving towards the ground station, the downlink frequency will appear to be higher than normal.
Most transponders operate on a bent pipe (i.e., u-bend) principle, sending back to Earth what goes into the conduit with only amplification and a shift from uplink to downlink frequency. However, some modern satellites use on-board processing, where the signal is demodulated, decoded, re-encoded and modulated aboard the satellite.
This table contains examples of downlink frequency assignments; Satellite Frequency Band Terra: 8212.5 MHz: 8175-8215 MHz METEOROLOGICAL-SATELLITE SERVICE Earth exploration-satellite service Aqua: 8160 MHz: 8025-8175 MHz: Earth exploration-satellite service NOAA 17,18 1707 MHz 1700-1710 MHz: Meteorological-satellite service: ERS-2 (High rate ...
Nearly all C-band communication satellites use the band of frequencies from 3.7 to 4.2 GHz for their downlinks, and the band of frequencies from 5.925 to 6.425 GHz for their uplinks. Note that by using the band from 3.7 to 4.0 GHz, this C band overlaps somewhat with the IEEE S band for radars.
The final satellite was launched on 26 March 2020. AEHF is backward compatible with, and replaces, the older Milstar system and will operate at 44 GHz uplink (extremely high frequency (EHF) band) and 20 GHz downlink (super high frequency (SHF) band). [4]
The first satellite of the Molniya series was launched on 23 April 1965 and was used for experimental transmission of TV signals from a Moscow uplink station to downlink stations located in Siberia and the Russian Far East, in Norilsk, Khabarovsk, Magadan and Vladivostok.
For certain phase modulation (PM) downlinks, the uplink to downlink frequency ratio was exactly 221/240, with a coherent transponders used. A phase locked loop on the spacecraft multiplied the uplink carrier frequency by 240/221 to produce the downlink carrier frequency. A local oscillator produced the downlink carrier if the uplink was not ...
Pertaining to radiocommunication service, a downlink (DL or D/L) is the portion of a feeder link used for the transmission of signals from a space radio station, space radio system or high altitude platform station to an earth station. In the context of satellite communications, a downlink (DL) is the link from a satellite to a ground station.