WIDE BAND SENSITIVITY MEASUREMENTS on the VLBA

A series of observations were made between 15 June and 9 July 1995 in an attempt to determine the system temperature, gain, and SEFD (System Equivalent Flux Density) for each antenna of the VLBA as a function of frequency for all bands. Each band was divided evenly into frequencies which extended beyond the nominal bandwidth. This was done to test antenna performance across the full band and especially near the edges of the lters. The complete range of observed frequencies is presented in Table 1. Various sources (see Table 2) were observed with pointing patterns speci ed in SCHED. Observations at 7mm and 1cm were made using the PTVLBA pointing pattern. This is a 10-point pattern which traces o {source! 1/2 beam! on{source! 1/2 beam ! o {source in both azimuth and elevation. All other bands were observed using a 3-point pattern which traced o -source ! on{source ! o {source in azimuth only. At all bands up to 2cm, full frequency coverage was obtained. This means that any strong RFI showed up in the original system temperatures. However these were not necessarily consistent from day to day. Many such spikes were edited out of the data, often causing small gaps in the plots. Note that other projects are in progress to do a better job of measuring RFI. The analysis of the data utilized measurements of system temperature and antenna temperature from the observations as derived by the standard program, TSM. A new program, PLOTBAND, was then used to derive gains and SEFDs. The gain for the antennas was calculated as :