EMIR (Eight MIxer Receiver)
Call for Proposals
Overview
The new receiver EMIR (Fig.1) is scheduled for installation and commissioning at the 30m telescope in March through April 2009. EMIR will replace the current single pixel heterodyne receivers A/B100, C/D150, A/B230, and C/D270. HERA, the bolometers, and the backends are unchanged. EMIR will provide a minimum instantaneous and width of 4 GHz in each of the two orthogonal linear polarizations for the 3, 2, 1.3 and 0.9mm atmospheric windows (Fig.2). In addition to the vast increase in bandwidth, the receiver is expected to offer considerably improved noise performance, a stable alignment between bands, and other practical advantages.
The four EMIR bands are designated as E090, E150, E230, and E330 according to their approximate center frequencies in GHz. While the E150 and E230 bands have SSB mixers with a single sideband available at a time, the E090 and E330 bands can be operated in 2SB mode where both sidebands are available for connection to backends. Furthermore, the E090 band is built in a technology that offers 8 GHz instantaneous bandwidth per sideband and polarization. Both polarizations of a given band will always be tuned to the same frequency as they share a single common local oscillator. The tuning ranges of the 4 bands, the typical receiver noise temperatures, and other parameters are listed in Tab.1.
EMIR will for the first time in the history of the 30m telescope provide a permanently available high sensitivity E330 band, opening this atmospheric window for regular use under good weather conditions. As commissioning of this channel will be difficult and time consuming during the summer semester, only a maximum of total 20 hours observing time will be available for regular proposals for this semester. The proposed targets should ideally be pointlike and available during nighttime in fall. The observations will be made as service observing with shared risk.
At the time of writing, EMIR is undergoing final tests in the receiver laboratory. Precise figures of EMIR's performance at the telescope will not be known before the proposal deadline. The Observatory will nevertheless make an effort to publish the results of the commisisoning available as soon as possible on this wiki page. The interested astronomer may also find more detailed technical information on EMIR under this URL. IRAM staff is also available to help astronomers with the preparation of EMIR (and other) proposals.
Selection of EMIR bands
Before reaching the Nasmyth mirrors, the four beams of the EMIR bands pass through warm optics that contains switchable mirrors and dichroic elements for redirection of the beams towards calibration loads and for combining beams. In its simplest mode, the warm optics unit selects one single EMIR band for observation. This mode avoids the use of the slightly lossy dichroic elements and therefore offers the best receiver noise temperatures.
Three dichroic mirrors are available for combining either the E090 and E150 beams, or the E090 and E2230 beams, or the E150 and E330 beams (Tab.1). The combination of bands is not polarization selective, i.e. the combined bands will stay dual polarization. The small loss of these dichroics increases however the receiver temperatures by 10 - 15 K. The observer is therefore adviced to carefully evaluate whether an observation involving two different bands is more efficiently made in parallel or in series.
Connection to backends
The remarkable bandwidth of EMIR of altogether 64 GHz faces 2 limitations of the existing 30m hardware: (1) the four IF cables can transport only 4 GHz each (the $4\times4$ GHz bottleneck) and (2) only at low spectral resolution are there enough backends to cover the 16 GHz which pass through the bottleneck.
A new IF switch box in the receiver cabin allows to select 4 EMIR channels of 4 GHz bandwidth each from 16 inputs. The 4 channels of 8 GHz width available from E090 are rearranged by the IF switch box into 4 pairs of inner and outer 4 GHz wide channels. The box can handle all plausible single band observations as well as the band combinations indicated in Tab.1. A full list of possible switch settings is available on the 30m web site.
The selected 4 output channels are sent via the IF cables to a new backend distribution unit which provides copies of these 4 channels to a range of backends processors which then prepare the IF signals for distribution to the spectrometers. Three new backend processors have been build to feed the new 4 GHz wide IF channels to the existing backends:
The WILMA processor rearranges the four incoming 4 GHz wide IF channels into 16 channels of 1 GHz width which can be processed by 16 WILMA autocorrelator units. Since each unit provides 512 spectral channels of 2 MHz, sufficient backend power is available at low spectral resolution for full coverage of the $4\times4$ GHz bottleneck.
The 4 MHz processor rearranges any two incoming 4 GHz wide IF channels into 8 slices of 1 GHz width for processing in 8 units of the 4 MHz filter bank. 2x4 GHz of EMIR bandwidth are thus covered at 4 MHz resolution.
The narrow band processor prepares the 4 incoming IF channels for input into the 1 MHz filterbank and VESPA. Only the central part of the 4 GHz IF channels is accessible to these backends. Inside this central part (1 GHz for the filterbank and 640 MHz for VESPA), these backends can be configured as before. The VLBI
terminal is also fed from this processor.
Calibration issues
Velocity scales
Update of PaKo
Observations time estimator
Details
Losses of dichroics
Settings of the IF switch box
Velocity scales
Results of Commissioning
TBD