EMIR Commissioning Report

The Commissioning team: Juan Penalver, Hans Ungerechts, Helmut Wiesemeyer, Albrecht Sievers, Gabriel Paubert, Walter Brunswig, Guillermo Quintana-Lacaci, Denise Riquelme, Rebeca Aladro, Breezy Ocana, Manolo Ruiz, Melanie Krips, Sascha Trippe, Dirk Muders, Albert Greve, Clemens Thum, Karl Schuster, Carsten Kramer

Abstract. Here, we report on the results of the commissioning of the new Eight Mixer Receiver at the IRAM 30m telescope, between end of March and end of April 2009. The first results are very promising. The observed alignment between the polarisations and between the bands is better than 1 arcsec. The observed telescope efficiencies (forward, main beam, aperture) are according to expecations. Spectral line observations were conducted with all observing modes, using all spectrometers, with the exception of the 1MHz filterbank, which still needs to be commissioned.

EMIR is not only hardware. Major parts of the software had to be rewritten. This concerns the receiver control software, parts of the "New Control System" and, of course, the PaKo user interface. In addition, the entire software producing the data had to be thoroughly revised: the read-out of the spectrometers into data streams, the transformation into IMBfits raw data, and the final transformation into calibrated data on the so-called TA* scale. A very significant part of the commissioning period was spent debugging this software, addressing all kinds of frequency swaps and shifts and plenty of wrong labels.

Routine observations with EMIR started on April, 28, without encountering major obstacles since then.

Related documents available on request:

Continuum Observations

Continuum backends

At present, only the central 1GHz of each 4GHz chunk are being used for continuum detection. Broad band 4GHz wide continuum detectors are in preparation.

Nasmyth Offsets

EMIR has two beams seperated by 90arcsec on the sky. Several pointing sessions were conducted to determine the Nasmyth offsets to be -39.0"/+5.5" for the right beam and +51.0"/+5.5" for the left beam. Each pointing session consists of observations of several dozen of point sources distributed over the sky. The right beam is used for single band E0 or E2 observations, and for dual band E0/E2 and E0/E1 observations. The left beam is used for E1, E3, E1/E3. At present, the observer has to set the Nasmyth offsets in PaKo. They are not yet set automatically when switching the EMIR setup.



The above figure shows the alignment between the four EMIR bands and between the two polarisations of each band. The overall alignment is better than 1 arcsec.



The above figure shows the focus between different polarisations of the same band. There are no significant differences between these foci.


This figure shows the focus between different bands. The largest deviation is about 0.3 mm, similar to the situation with the ABCD receivers. For dual band observations, the telescope should be focussed to the high frequency band.

We also made focus scans in lateral (x, y) directions, however, with inconclusive results. The observed telescope efficiencies indicate that the telescope is well focussed.

Telescope Efficiencies

The main beam and aperture efficiencies, and the beam widths, were derived from Mars observations. The observations on April, 4th, were conducted at an elevation of 43 deg, i.e. near the maximum of the gain elevation curve. The observations on March, 29th, were conducted at elevations between 29deg and 44deg. The ellipticity of the beams is better than 90% in all cases. Mars was pointlike with a diameter of 4arcsec.

The forward efficiencies were derived from Skydips. All skydip observations conducted in the week before Apr, 1st, resulted in the following efficiencies:

The analysis of the skydips was done manually. The atmospheric temperature Tatm was derived with the program ATM. The agreement between the atmospheric opacity derived from the skydips and those determined by the standard (chopper-wheel) calibration, agree very well. At present, it is not clear whether the slight 3% difference in forward efficienciers found between observations with band E1 together with E0, or together with E3, i.e. with different dichroics, is significant or not.

Errorbeam observations

We conducted total power scans across the full moon to study the telescope error beams. The results agree with results previously obtained with the ABCD receivers, as expected.

Pointing & Flux monitoring

Pointing scans were conducted in the traditional beam switching mode, in wobbler switching mode, and in total power mode. Under very good atmospheric conditions, the total power mode produced very good results. The beam switching mode suffered from spikes, a problem which is already known from the ABCD receivers. This will be tackled, otherwise wobbler switching may be the more efficient observing mode.

Spectral line observations


During commissioning, we used the 4MHz filterbank and the two auto correlator backends WILMA and VESPA, partly in parallel. The 1MHz filterbank will be commissioned asap.

A variety of VESPA setups were checked, covering the range of resolutions between 3kHz and 1.25MHz and a wide range of bandwidths. VESPA parallel mode was also checked. However, as a reminder, it is not possible to check all possible setups. A tool to validate the selected VESPA setup in PaKo has been implemented.

Observing modes

The following switching modes were re-commissioned: position switching (onoff), wobbler switching, and frequency switching. Beam switching was checked using the continuum backends. The on-the-fly mapping mode was re-commissioned, in combination with position switching and with frequency switching.

EMIR setups

The following EMIR setups were requested in the proposals for this summer semester and have been commissioned. The Code corresponds to the table created by S.Navarro describing possible setups of the switch box BAND_COMBINATIONS.pdf. The listed Bandwidth is the total bandwidth covered by the resulting spectra, given to about 0.5GHz accuracy.

The following Figure shows the frequencies of the band edges and centers of the lower and upper sidebands, and the inner and outer bands. Note that the band edges and center are not exactly at multiples of 2GHz relative to the local oscillator. This is due to the IF distribution. The backends are centered near the band centers. VESPA is centered at 6.25 or 9.43GHz. For WILMA, the inner and outer bands have 0.1GHz overlap. The inner band runs from 4.125 to 7.845GHz. The outer band runs from 7.835 to 11.555GHz.


Band Edges

We checked that the following band edges (center of 4GHz IF) can be reached:



Ripples and spurious signals


Receiver gain ratios

Status of Band 4 commissioning

Science verification



Remaining steps

EmirCommissioningReportOldDraft (last edited 2009-05-26 08:24:28 by visitor13)