APEX-2 characteristics

Receiver Temperatures

Current performance

The noise temperatures of the receiver are measured continuously by fetching the corresponding information from our observation database. The image below shows the latest results, using data obtained between June 2014 and January 2015.

Receiver temperature vs. time

Because of improvements of the receiver, the receiver temperatures now are significant below those measured after the installation in 2008. For selected lines/frequencies (those which form part of the APEX-2 calibration plan), we have collected the numbers since 2008.

Frequency [GHz]	267.558	271.981	293.912	304.070	304.070	329.331	330.588	330.588
Spectral Line	HCO+(3-2)L	HNC(3-2)L	CS(6-5)L	SO(8-7)L	SO(8-7)U	C18O(3-2)L	13CO(3-2)L	13CO(3-2)U
Trec vs. time¹
Frequency [GHz]	338.405	342.883	345.796	345.796	354.505	356.734	362.736
Spectral Line	CH3OH(7-6)L	CS(7-6)L	12CO(3-2)L	12CO(3-2)U	HCN(4-3)U	HCO+(4-3)U	H2CO(5-4)U
Trec vs. time¹

¹ The high values for the receiver temperatures in the first half of 2014 visible in some plots are a result of temporary receiver nonlinearities; see SHeFI issues Mar-Jun 2014.

Just for completeness, we still maintain information about the receiver temperatures measured during the commissioning of the receiver in 2008. Keep in mind that those numbers do no reflect the current receiver performance.

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Sideband Rejection

The sideband rejection was measured during the commissioning of the instrument in 2008. It is generally better than 15dB, depending on frequency.
First measurements had been taken on site with the receiver tuned to the CO(2-1) frequency in USB. We used a spectrum analyzer and injected a narrow test signal which is moved in frequency to span the 4-8 GHz of the IF (Results).
Additional measurements were made on-sky using strong sources and the receiver was tuned to discrete frequencies, alternatively in LSB and USB to have the line either in the signal or image band. The results are summarized in the following table:

Source	Line @ sideband	Signal intensity [K]	Image intensity [K]	Rejection [dB]
IRAS16293	CO(3-2) USB	21.2	< 0.4	> 17
IRAS16293	CO(3-2) LSB	24.9	< 0.4	> 18
IRAS16293	13CO(3-2) USB	13.7	< 0.5	> 14
IRAS16293	13CO(3-2) LSB	16.5	< 0.5	> 15
IRAS16293	HCO+(4-3) USB	21.0	< 0.2	> 20
IRAS16293	HCO+(4-3) LSB	16.0	20.0	-1
IRC+10216	HCN(4-3) USB	26.7	0.8	15