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 depicted in Tab. 1. Note that they cannot be combined with HERA nor with the bolometers. Also listed are typical system temperatures which apply to average summer weather (7mm of water) 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 summer observing semester. 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 summer conditions (pwv = 7mm) 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.

receiver	polari-	combinations				tuning range	$T_{Rx}$(SSB)	$g_i$	$\nu _{IF}$	$\Delta \nu _{IF}$	$T^{\ast }_{sys}$	remark
	zation	1	2	3	4	GHz	K	dB	GHz	GHz	K
A100	V	1		3		80 - 115.5	60 - 80	$>20$	1.5	0.5	120
B100	H	1			4	81 - 115.5	60 - 80	$>20$	1.5	0.5	120	1
C150	V		2		4	129 - 183	70 - 125	15 - 25	4.0	1.0	200
D150	H		2	3		129 - 183	80 - 125	8 - 17	4.0	1.0	200
A230	V	1		3		197 - 266	85 - 150	12 - 17	4.0	1.0	450	2
B230	H	1			4	197 - 266	95 - 160	12 - 17	4.0	1.0	450	2
C270	V		2		4	241 - 281	125 - 250	10 - 20	4.0	1.0	1000	3
D270	H		2	3		241 - 281	150 - 250	9 - 13	4.0	1.0	1000	3
HERA	H/V					210 - 276	110 - 380	$\sim 10$	4.0	1.0	400	2, 4

1: tuning range extended to $\geq 72$ GHz under special conditions (see text)
2: noise increasing with frequency
3: performance at $\nu<275$ GHz; noisier above 275 GHz.
4: the V-array (2nd polarization) of HERA has slighly higher noise which may vary across the IF band; it should not be used for frequencies higher than 241 GHz.