Between early 1991 and mid 1995, a series of nine VLBI observations were carried out with the SHEVE array (at eight epochs) and with the VLBA (at four epochs, three of which overlapped with SHEVE observations) at a frequency of 8.4 GHz. Table 5.1 summerises the series of observations and lists the telescopes participating at each epoch.
Table 5.1: Observation log for Centaurus A 8.4 GHz observations
The high resolution SHEVE+VLBA data from 1992 November 22, 1993 July 3, and 1993 October 20 will be discussed in 
5.4. The discussion here will focus on a comparison of the lower resolution data from the nine epochs, those data obtained with the telescopes highlighted in Table 5.1.
The data from the SHEVE array were obtained and processed as described in chapter 2 to produce the images appearing in Figures 5.4 to 5.11. The image in Figure 5.12 is from VLBA data alone. The VLBA observations of 1995 July 3 were made in VLBA mode using a 32 MHz bandwidth, with single bit sampling. The data were correlated at the VLBA correlator in Soccoro then fringe-fitted with FRING in AIPS before being calibrated from system temperatures and gain-elevation curves in the Caltech VLBI package. Imaging proceeded as described in chapter 2.
Each image is dominated by the bright core component at the south-west end of the source and shows a strong jet along a position angle of 51 
. The typical dynamic range achieved in imaging these data was 100:1. From a cursory inspection of the images it is clear that the source is structurally complex and changes in the source are apparent between epochs, and over the full 4.3 years of the observations. To quantify these changes a model-fitting analysis of the data was made at each epoch. The models were then compared to obtain some understanding of the structure and evolution in Centaurus A on the sub-pc-scale during this period and in an attempt to quantify the effects of the (sometimes significant) differences in the u-v coverage between the epochs.
