Receivers

As many as four receivers are mounted simultaneously at offset Cassegrain foci on the telescope. Receiver selection is by means of a rotating central mirror and can be accomplished in minutes. The receivers are configured remotely from the control room with a computer-aided tuning system. The standard receiver system at the 12 Meter consists of a 4 K closed-cycle cryostat containing up to 8 SIS receivers. A complete set of dual-channel SIS receivers is operational over the atmospheric windows from 68 to 300 GHz range. Table 2 indicates current performance.

 

Table 2: 12m Receiver Characteristics

 

Receiver1	Wavelength Range (mm)	Approximate Tsys(SSB)2 (K)
68-90 GHz SIS	4.4-3.3	170-225
90-116 GHz SIS	3.3-2.6	160-350 @ 115 GHz
130-170 GHz SIS	2.3-1.8	180-400
200-265 GHz SIS3	1.5-1.1	400-900
260-300 GHz SIS	1.15-1.0	800-1200
215-245 GHz 8-Beam SIS	1.4-1.3	700

¹ All single-beam receivers have two orthogonal polarization channels.

² Receiver temperatures include all receiver optics.

³ Receiver noise is around 200 K single sideband for most of the band, but increases somewhat at the high-frequency end of the band.