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.