The radio source PKS 1718-649 lies at a distance of approximately 56 Mpc (z=0.014, adopting H=75 km/s/Mpc). It was optically identified as the galaxy NGC 6328 by Savage [1976] and has been extensively studied at optical wavelengths by Fosbury et al. [1977], Carswell et al. [1984], Filippenko [1985], and Keel and Windhorst [1991] since it is a nearby galaxy and a source of strong optical emission lines. The active nucleus at the centre of the galaxy is generally classified as a Low Ionisation Nuclear Emission Region (LINER). The optical morphology of the galaxy is unusual in that it appears to have a central brightness profile which follows an r 
de Vaucoluers law typical for elliptical galaxies but has spiral arms which extend out approximately 20 kpc from the nucleus [Véron-Cetty et al. 1995].
The properties of the radio source, until recently, were not as well determined as the optical properties of the galaxy. The monochromatic luminosity of the radio source at 1.4 GHz is approximately 1.2 
10 
W/Hz if a distance of 56 Mpc is assumed. Fosbury et al. [1977] observed the galaxy at the HI transition and inferred that a large fraction, 6%, of the galaxy mass consisted of neutral Hydrogen. Véron-Cetty et al. [1995] showed that the neutral Hydrogen exists in an incomplete ring, 37 kpc in diameter, and an envelope which extends over 180 kpc. Fosbury et al. [1977] also presented the radio spectrum between 408 MHz and 5 GHz, showing it to be inverted, indicating the presence of compact radio emission. The first VLBI observations of the compact radio source in PKS 1718-649 were undertaken as part of the first SHEVE experiment in 1982. The resulting data were sparse but could be modelled in terms of two components, separated by approximately 15 mas along a position angle of approximately 
[Preston et al. 1989].
The combination of strong and active compact radio source and spiral galaxy is an unusual one. Fosbury et al. [1977] point out that PKS 1718-649 is among the few strong, flat or complex radio spectrum sources to be associated with a galaxy, although more extreme examples exist, such as PKS 1934-638. PKS 1718-649 is, therefore, an interesting target for a more comprehensive investigation of the radio source. In particular, the proximity of this object provides the opportunity for high spatial resolution imaging of the compact radio structure since 1 mas is approximately equal to 0.25 pc at the red shift of z=0.014 (H=75 km/s/Mpc). Furthermore, the proximity of the galaxy allows relatively high resolution studies of the emission from the host galaxy at other wavelengths.
The aims of this chapter are to:
1] Present the first extensive investigation of the PKS 1718-649 radio source and to review previous observations at other wavelengths.
2] Arrive at an interpretation for this unusual object from a
consideration of the available data.
In this chapter the first VLBI imaging observations of the compact radio emission from PKS 1718-649 are presented in 
7.2. In 7.3, the results from polarimetric radio imaging at the ATCA are described. Also in 7.3, total flux density measurements which extend the PKS 1718-649 radio spectrum up to 230 GHz are presented. Finally a discussion of the nature of the radio source and its host galaxy is given in 7.5, paying particular attention to two possible interpretations.