Figure 5: Status of the 230 GHz G2 receiver at Pico Veleta after installation of
the new SIS mixer in February 94 and after the change of the horn
in January 95. The receiver band is improved by 10 GHz. The noise
temperature is measured in front of receiver.
A mixer with a SINS Nb-Al oxide-Al-Nb quasi-particle tunnel junction
was prepared for the 0.87 mm band. This type of junction is nearly
free of pair currents and related perturbations. Potentially
having a better stability of operation, this mixer works without
the magnetic field normally used at submillimeter wavelengths to suppress
pair currents. We achieve a receiver DSB noise temperature of
about 130 K at 310 GHz. Note that this receiver noise was reached
with enormous junction 
, about 30 times
more than optimum. With improvement of the SIN junction technology,
receiver noise with an SIN mixer may be about twice the noise of the SIS
receiver.