- Feed
- Cryostat (including refrigerator and transparent membrane)
- LNA
- Pcal Coupler
- Linear to circular converter
- Data Down-link
- Calibration Systems
- Radiometry fundamentals (link to Bill's Helsinki VLBI school presentation)
The receiver front end is the part of the receiver located near the focus of the antenna.
The most important components of the VGOS receiver front end signal chain are the;
- Feeds,
- Calibration signal couplers
- Low noise amplifiers (LNAs).
Since, for sensistivity reasons, low system noise temperature (Tsys) is a priority, these components are generally kept at a very low physical termperature inside a refrigerated cryostat. A transparent window is required to allow RF signals to penetrate the cryostat and read the feed.
In addition to the elements of the direct signal chain, other components are usually included in a VGOS receiver front end:
- Pulse cal generator and noise diode
- Optionaly converter from linear to circular polarization
- Conditioners for RF signal transmission to the VGOS control room and receiver back end