The single pixel heterodyne receivers

Four dual polarization SIS receivers are available at the telescope for the upcoming observing season. They are designated according to the dewar in which they are housed (A, B, C, or D), followed by the center frequency (in GHz) of their tuning range. Their main characteristics are summarised in Tab. 1. All receivers are linearly polarized with the E-vectors, before rotation in the Martin-Puplett interferometers, either horizontal or vertical in the Nasmyth cabin. Up to four of these eight receivers can be combined for simultaneous observations in the four ways designated as AB, CD, AD, and BC. These are the only valid combinations and they are depicted in Tab. 1. Note that single pixel receivers cannot be combined with HERA nor with the bolometers. Also listed are typical system temperatures which apply to normal winter weather (4mm) at the center of the tuning range and at 45$^\circ$ elevation. All receivers are tuned by the operators from the control room. Experience shows that it normally takes not more than 15 min to tune four such receivers.

Table 1: Heterodyne receivers available for the next winter observing season. Performance figures are based on recent measurements at the telescope. $T^{\ast}_{sys}$ is the SSB system temperature in the $T^\ast_A$ scale at the nominal center of the tuning range, assuming average winter conditions (4mm pwv) and 45$^\circ$ elevation. $g_i$ is the rejection factor of the image side band. $\nu_{IF}$ and $\Delta\nu_{IF}$ are the IF center frequency and width. Note that the 8 standard receivers can be combined in 4 different ways.

receiver		polar-		combinations				tuning range		$T_{Rx}$(SSB)		$g_i$	$\nu_{IF}$	$\Delta\nu_{IF}$		$T^{\ast}_{sys}$	remark
		ization		AB		CD		AD		BC		GHz	K	dB		GHz	GHz	K
A100		V		1				3				80 - 115.5	45 - 65	$>20$		1.5	0.5	120	1
B100		H		1						4		81 - 115.5	60 - 85	$>20$		1.5	0.5	130	1
C150		V				2				4		129 - 183	70 - 115	15 - 25		4.0	1.0	200
D150		H				2		3				129 - 183	60 - 150	8 - 17		4.0	1.0	200
A230		V		1				3				197 - 266	85 - 185	12 - 17		4.0	1.0	420
B230		H		1						4		197 - 266	95 - 160	12 - 17		4.0	1.0	420
C270		V				2				4		241 - 281	125 - 290	10 - 20		4.0	1.0	900	2
D270		H				2		3				241 - 281	130 - 300	9 - 13		4.0	1.0	900	2
HERA		H,V										210 - 276	110 - 380	$\sim 10$		4.0	1.0	400	3

1: tuning range extended to $\geq72$ GHz under special conditions (see text)
2: noise increasing with frequency
3: tuning parameters are not yet complete