EAFC

Enhanced Automatic Frequency Control - What is it?

Orbit Research Ltd specialises in the design and manufacture of Automatic Frequency Control systems for satellite communication. Our robust and highly reliable designs are well proven and respected.

Automatic Frequency Control is used to modify the frequency of communication carriers transmitted and received from a satellite communication earth station. It works by comparing the frequency of a very accurate local reference to a signal that has been transmitted over the satellite. The difference in frequency can be used to determine the error on the traffic carriers and hence a correction can be made to the frequency converters that both transmit and receive the traffic signals.

Most communication satellites are in a Geostationary Orbit (ie they have an orbital period equal to one day, and they are located over the equator). Geostationary satellites appear in a fixed location in the sky. However, gravitational interaction of the sun and moon tend to pull the geostationary satellite off course over a period of a few months and this gives rise to Doppler shifts (or frequency variations) as the satellite moves in a slightly eccentric orbit. Satellite operators correct their satellites' position from time to time.

The communication signals in the Inmarsat system are designed to use very narrow bandwidths and hence the Doppler shift experienced by the signal as it is transmitted over the satellite is a much higher percentage of the signal bandwidth than a normal satellite signal. Because of this Inmarsat earth stations use a system called Enhanced Automatic Frequency Control to correct their signals.

An Enhanced AFC receiver can determine the amount of Doppler shift on the received signal by measuring the signal over a period of time. It can then calculate the required amount of correction that must be applied to the traffic signals.

Orbit Research is one of the few manufacturers in the world supplying this type of specialised equipment. Our system is based on many years of experience with major telecom operators. Our system is typically an order of magnitude more accurate than other competing systems.

EAFC Description | EAFC Specification