Frequency tuning for satellite ground stations

In a satellite communications network having a first terminal for transmitting and receiving signals, a second terminal in communication with the first terminal for transmitting signals, a plurality of other terminals in communication with the first and second terminals and a satellite for receiving signals from the terminals and retransmitting them, the frequency of the retransmitted signals being offset from the frequency at which the signals were received, a method for compensating a transmit frequency of the second terminal for satellite and terminal frequency offset comprising:

• transmitting a signal from the first terminal to the satellite at a first frequency for retransmission to the first and second terminals;
• receiving the signal transmitted by the first terminal from the satellite at the first terminal at a second frequency, the second frequency being offset from the first frequency by the satellite;
• measuring, at the first terminal, the difference between the first frequency and the second frequency to obtain a first offset;
• transmitting the first offset from the first terminal to the second terminal;
• receiving, at the second terminal, a signal from an other terminal via the satellite for which the transmission frequency from the other terminal is known;
• subtracting, at the second terminal, the known other terminal transmission frequency and the first offset from the frequency of the received signal to obtain the terminal offset;
• adding, at the second terminal, the difference between the terminal offset and the first offset to the second terminal transmit frequency.