A calibration system for the Green Bank Telescope 4mm receiver: On-telescope, RFI-free calibration for 68–92 GHz observations

Calibration for spectral line observations covering 68–92 GHz on the Green Bank Telescope uses a different calibration scheme than lower frequency receivers. In addition and extremely important is that any calibration scheme must not generate radio frequency interference (RFI) to other experiments ongoing at the Green Bank Observatory. An asynchronous logic network interfaces between the telescope control system, a brushless AC motor and three bit position encoding to place or remove reflectors, absorber or a quarter wave plate in the beam of the feeds to enable observers to calibrate their data during observations or configure the receiver for Very Long Baseline Interferometer network observations. This system is free of RFI that schemes utilizing more commonly available technology create.