Introduction

This document describes the FITS formatted file written on each scan, by the Tracking Local Oscillator (LO1). One file is written for each of the two synthesisers, LO1A and LO1B. Normally, LO1A will be used for the tracking LO, and LO1B as a test-tone generator. The LO1 FITS files contain a complete description of the setup of the LO; information as to how the LO is connected to the rest of the system is described in the IF Manager FITS file.

LO1 demands sent to the actual synthesiser consists of two components; the base values, which will smoothly vary with time if Doppler tracking is enabled, and offset values which are added to these base values, to implement frequency switching for example. These values are stored in the LO1TBL and STATE binary tables respectively.

In the majority of cases, the LO1 will be asked to track a single source velocity. In some cases however (e.g. solar system objects) it is possible for the LO1 to be passed a ``source velocity track''; an array of records containing source velocity values, first and second derivatives for a series of times. aips++ needs to know the desired source velocity so that it can ``reverse'' the Doppler tracking calculations to allow spectra to be presented in the rest frame of the source. This velocity should be obtained from the GO (User Interface) FITS file. However, for engineering purposes, the actual source velocity track will be stored in the LO1 FITS file in the SOUVEL binary table.