On 2015-02-07 02:48, David Woolley wrote: > What the satellites do do is to to transmit some additional information > about ionospheric propagation, which allows for receiver to compensate > for the signals travelling slower than the speed of light in vacuo.
None of the primary satellites in the constellation of the Navstar system (those with PRNs less than 100) transmit ionospheric information over L1. Ionospheric delay is a function of path length through the ionoshphere so it varies depending on the location of the satellite and the receiver. The WAAS satellites (PRN > 100) can provide some corrective data on a side-channel that are folded into the calculations on the receiver but the receiver must be able to use the WAAS signal to do this. WAAS provides a more detailed ionospheric correction using a series of ground reference stations whose positions are known via ground surveys and transmitted by two geostationary satellites. For Navstar it is not available globally, only over North America. Military Navstar receivers use a minimum of two different frequencies (L1 1575.42 MHz, L2 1227.60 MHz) and can utilize that to compute ionospheric delays from each satellite in near real-time at the receiver's location (in addition to using WAAS). The newest satellites are capable of transmitting a civilian code on L2 (L2C). Receivers that can use L2C in theory could also perform the ionospheric compensation calculations but it will take some time before the entire constellation is capable of transmitting L2C. _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
