3mm (2mm) VLBI

Construction

A cryogenic SIS receiver designed at IAP, Russia. SIS mixer mounts inside the dewar are cooled down to 4.5 K with a helium closed cycle refrigerator. Two mixers for 3 mm allow the possibility for simultaneous circular dual-polarization measurements. The local oscillator source for the 3 mm band is an InP Gunn-oscillator. For phase locking the Rohde & Schwarz synthesizer is used with a harmonic mixer to create the PLL IF signal at 275 MHz. This mixing product is divided by 11 and compared with the 5 MHz frequency standard (multiplied by 5) for PLL feedback. Cryogenic HEMT IF amplifiers with center frequency at 4 GHz and bandwidth of 1 GHz followed by amplifiers at room temperature are used for continuum output. With the second LO at 3.2 GHz this IF band is transferred to the standard VLBI band of 0.5 - 1.0 GHz. The 3 mm part of the receiver is currently disabled. 2 mm operation confirmed in the laboratory.