Green Bank's Spectral Processor, designed by NRAO engineers to exploit the large antenna advantages of the site's former 300 foot telescope, is a complex instrument used primarily by astronomers to study pulsars. A pulsar is a highly magnetized neutron star with a radius of 10-15 km and having a somewhat greater mass than the Sun, which has a radius of approximately 1 million kilometers. See Figures 1 and 2 for examples of both radio and optical depictions of a pulsar. Radiation from a pulsar is beamed out along its magnetic poles. These "pulses" of radiation are received as the beam crosses the Earth. A simple analogy would be the beam of light from a lighthouse, flashing at an observer within viewing distance as it rotates. Being enormous cosmic flywheels with a tick attached, pulsars also make some of the best clocks known. The spectral processor has been used to study and obtain data on pulsars for many years. The instrument was used extensively at Green Bank's 140 foot equatorial telescope where it was employed until 1999. It now joins a host of other telescope backends to support astronomical research conducted with the new GBT. An example of the types of science expected with this telescope, to include pulsar work, is depicted in Figure 3. The spectral processor is capable of especially high dynamic range, which is useful at frequencies where interference is severe. Though designed in the early 1980's, the instrument remains a viable tool, capable of operating under numerous configurations and observing modes depending on the astronomers observing objective.
Figure 1
Figure 2
Figure 3