- Antenna
- Receiver Front End
- Data Down-link
- Receiver Back End
- Calibration Systems
- Monitor/Control/Communications
- Correlator
- Fringe processing
- Direct Sampling Receiver
The VGOS broadband system receives dual polarization signals in the 2 to 14 GHz frequency range and processes them in four optimally placed 1024 MHZ bands. Incoming radiation is collected by antenna reflectors and converted to electrical signals by the antenna feed. The receiver is divided into a receiver front end located near the antenna focus (including mainly the feed, low noise amplifers (LNAs) and calibration electronics) and a receiver back end usually located in the station control room (including a signal distributor, down converters, digital back ends (including samplers), a data system, and a monitor/control/communication system). Timing stability is critical in VLBI so a Hydrogen maser is used as frequency reference. Calibration systems are needed for phase, delay and amplitude alignment. VLBI requires that signals from a number of antennas be brought together and correlated. The outputs of the correlator are correlation coefficients, which are used to produce amplitudes and phases for astronomical imaging and inter-station delay measurements for geodetic processing. A direct sampling receiver alternative is also being implemented that samples the RF signals directly at the output of the receiver front end and then does all remaining processing digitally.