SIS tunnel junctions on high Tc superconductors, when operated as quasiparticle mixers, offer the possibility of low- noise photon detection in the THz regime. Such devices require junctions with sharp current onsets at the gap voltage, 2A/e, and low sub-gap conductances. The bismuthate, Bai_xKxBi03, (Tc=25K) displays ideal , BCS, quasiparticle characteristics at low temperatures, however, at temperatures (TÃ¢â‚¬â€Tc/2) there is evidence of strong quasiparticle damping which may inhibit device performance. The cuprates typically display non-ideal quasiparticle characteristics but recent data for the new Hg- based cuprates (Tc=96K) are promising in that they display very low and flat sub-gap conductances. Proximity effect tunnel junctions on Bi2Sr2CaCu208/Au bilayers show improved sub-gap characteristics and indicate that this approach may be suitable for mixer development.