The GBT Spectrometer provides the observer with a remarkable variety of spectral line observing modes, allowing the scientific return of their experiment to be optimized. It is a modular system, with 4 (nearly) identical quadrants. The quadrants may be used independently or grouped together into banks of 1, 2 or 4 quadrants, providing the observer with 3 different levels of spectral resolution for each observing mode. When the 4 quadrants are independently operated, they can be configured in four different modes during a single observation.

The spectrometer performs auto correlations of the input signals. The input signals may be

• Dual polarization IFs in a selected frequency range;
• Up to four selected frequency ranges in a single polarization;
• IF inputs from different feeds of multi-feed receivers;
• Combinations of the preceding at different spectral resolutions.

The spectrometer modes are divided into two major types, wide bandwidth, low resolution and narrow bandwidth, high resolution. The maximum bandwidth is 6400 MHz at 391,000 Hz resolution and maximum resolution is 49 Hz in a 12.5 MHz bandwidth.