HRPT is the High Resolution Picture Transmission format. The different sensors on board the NOAA TIROS series of satellites transmit HRPT formatted data. The frequency band for HRPT is L Band which is about 1.670–1.710 GHz. Not sure what you mean by lb1 - perhaps Level 1b? If so Level 1b formatted data contains the full resolution dataset from the satellite sensor along with time stamps, data quality indicators, calibration coefficients and georeferencing information. For the NOAA HRPT data Level 1b is the result of the next step of processing following Level 0 and Level 1a.