The observed spectrum has to be corrected for the telescope response as a function of frequency across the band to obtain an estimate of the true spectrum. The telescope response is in general complex with both amplitude and phase variations across the observing band. This overall response across the band can be split into two components : (1) an overall gain (amplitude and phase) of the telescope for a reference radio frequency (RF) within the observing band, and (2) a variation of this gain across channels (the bandshape). The telescope response is thus a combination of RF gain calibration and IF bandshape calibration. This way of looking at the telescope calibration is useful since the requirements for determining these two parts of the telescope response can be different. For e.g., the IF bandshape variation is expected to be slower in time than the RF gain variation and hence need to be estimated less often. The spectral scale for the IF bandshape is however narrower compared to that of the RF gain.