
\begin{figure}[ht]   
  \centering   
  \includegraphics[angle=0,width=7.8cm]{emirOpen.eps}
  %\includegraphics[angle=0,width=5.0cm]{emirTrue.eps}
  \caption{EMIR during final integration  in the Grenoble
  receiver laboratory. One of the four dual--polarization mixer pairs
  is visible near the center of the photograph. The beams of the 4
  mixer pairs leave the dewar through 4 separate windows towards the
  top of the figure. Warm optics
  (not shown) can combine some of the 4 beams for observation of the
  same position on the sky (see Tab.~\ref{tab_emir_frontend}).
  \label{f:EMIR}   }
\end{figure} 



\subsection{EMIR }

\subsubsection{Overview }

%attachment:emir.bmp 
The new receiver \textbf{EMIR} (Fig.~\ref{f:EMIR}) 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 bandwidth of 4 GHz in each of the two
orthogonal linear polarizations for the  3, 2, 1.3 and 0.9\,mm
atmospheric windows (Fig.~\ref{f:atmos}).
 In addition to the vast increase in bandwidth compared to the old
 single pixel receivers, EMIR
is expected to offer %considerably 
significantly improved noise performance,
%and base line quality
a stable alignment between bands, and other practical advantages.  

\begin{table*}
  \begin{center}
  \caption[]{\label{tab_emir_frontend}
    {\small EMIR Frontend. Sky frequencies, F$_{\rm sky}$, refer to
      the center of the IF band. 2SB -- dual sideband mixers,
      SSB  -- single side band mixers, H/V -- horizontal and
      vertical polarizations, T$_{\rm sb}$ is the SSB receiver temperature
      in single band observations ({\it left}). For dual--band 
      observations, T$_{\rm db}$  includes a 15\,K noise 
      contribution from the dichroics ({\it right}).\rule[-1ex]{0em}{1ex}
      %\bf {clarify the combination of bands in the table and include the
      %single band options with their expected  
      %noise temperatures} 
    }}
  \begin{tabular}{|ccccccc|cccc|}
  \hline \hline
  EMIR & F$_{\rm sky}$ & mixer  & polari- & IF width & T$_{\rm sb}$ 
       & G$_{\rm im}$ & \multicolumn{3}{c}{combinations}&T$_{\rm db}$  
       \rule{0em}{3ex}\\
  band & GHz           & type   & zation  & GHz          
       &  K            & dB     &E\,0/2&E\,1/3 &E\,0/1& K \\[0.2ex]\hline
  E\,090 &\ 83 -- 117 & 2SB &H/V & 8& 50 & $>13$ &  X &   & X &\, 65 
                                                         \rule{0em}{3ex}\\
  E\,150 &129 -- 174 & SSB &H/V & 4& 50 & $>10$ &    & X & X & 65 \\
  E\,230 &200 -- 267 & SSB &H/V & 4& 50 & $>13$ &  X &   &   & 65 \\
  E\,330 &260 -- 360 & 2SB &H/V & 4& 70 & $>10$ &    & X &   & 85 \\
    \hline
  \end{tabular}
  \end{center}
\end{table*}

The four EMIR bands are designated as E\,090, E\,150, E\,230, and
E\,330 
%(or E\,0, E\,1, E\,2, and E\,3 for short) 
according to their approximate center frequencies in GHz.
While the E\,150 and E\,230 bands have SSB mixers with a single
sideband available at a time, the E\,090 and E\,330 bands 
are operated in 2SB mode where  both sidebands are available
for connection to backends. Furthermore,
the E\,090 band uses  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 as measured in the lab
are listed in Tab.~\ref{tab_emir_frontend}.

For the first time in the history of the 30m telescope,
EMIR will provide a permanently available high 
sensitivity E\,330 band, opening this atmospheric window for regular
use under good weather conditions.  
However, as commissioning of this band
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 point--like and  available during nighttime in fall.
%The observations will be made as service  observing with shared risk. 
we do not offer the 0.9\,mm band right now. A separate Call for
0.9\,mm observations may be issued in May in case that commissioning of this
band came to a positive conclusion.


\begin{figure*}[htb]   
  \centering   
  \includegraphics[angle=-90,width=11cm]{atm30m.eps}
  \caption{Atmospheric transmission at the 30m site between 60 and
    400~GHz for 1 and
    4mm of precipitable water vapor, derived from the ATM model. The EMIR
    bands are indicated and the frequencies of a few important
    molecular transitions are marked. \label{f:atmos}}
\end{figure*} 


%The receiver and connected backend selection
%electronics offer a wide but complex range of possibilities  
%in particular as also different bands can be combined by means of
%dichroic mirrors (see table 1 \& 2).  
%In case of questions please contact IRAM well in advance of the
%proposal deadline. 

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 make
the results of the commissioning available as soon as possible
on the 30m web site. The interested astronomer may also
find more detailed technical 
information on EMIR under this URL. IRAM staff is also be available to
help astronomers  with the preparation of EMIR (and other) proposals.


\subsubsection{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 E\,090 
and E\,150
beams, or the E\,090 and E\,230 beams, or the E\,150 and E\,330 beams
(Tab.~\ref{tab_emir_frontend}). The combination of bands is not
polarization selective, i.e. the combined bands will stay dual polarization.
The loss of these dichroics which is small over most of the accessible
frequency range, 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.





\subsubsection{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 {\bf IF switch box} in the receiver cabin allows to select 4
EMIR channels of 4 GHz bandwidth each from 16 inputs.\footnote{\ The 
4 channels of 8 GHz width available from E\,090  are rearranged 
by the IF switch box  into 4 pairs of inner and outer 4 GHz wide channels.}
%The outer channels are downconverted to 4-8 GHz,
%before entering the IF switch box. 
The box can handle all plausible single band observations as well as
the band combinations indicated in Tab.~\ref{tab_emir_frontend}. A full
list of possible switch settings is available on the 30m web site.
%({\it Carsten: if not true yet, we should provide easy access to Santiago's
%table shown as slide 12 in his EMIR presentation. Actually, this table
%needs an update following the $4\rightarrow8$ GHz bandwidth jump of
%E090. I do not think, though, that we show show this table here}).

The selected 4 output channels are sent via the IF cables to a new 
{\bf 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:
\begin{itemize}
\item[$\rhd$] The {\bf 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 this low spectral resolution for full coverage of the $4\times4$ GHz 
bottleneck. %of EMIR bandwidth. 
\item[$\rhd$] The {\bf 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. $2\times4$ GHz of EMIR bandwidth are
thus covered at 4 MHz resolution.
\item[$\rhd$] The {\bf ``narrow band backends'' 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.  
\end{itemize}
%
%In addition to adapting the spectroscopy backends, new continuum
%detectors of much increased bandwidth (Carsten: how nuch??) have been
%built. 


%\begin{table*}[htb]
%  \caption[]{\label{backend_processors}
%  {\small \bf {COMPLETE this table to indicate which combinations are possible to hook the various EMIR outputs to the various backends, I 
%  remember that not really all thinkable combinations were possible}
%  }}
%\begin{tabular}{cccccc}
%\hline \hline
%Backend & Type & Processor & Ch.spac. & Bandw. & Remarks \\
%\hline
%WILMA &autocorrelator &4x4 &2MHz &4x4GHz & \\
%4MHz &filterbank &4MHz &4MHz &8x1GHz &  \\
%1MHz &filterbank &narrow band &1MHz &1GHz &  \\
%VESPA &autocorrelator &narrow band &flexible &flexible &  \\
%VLBI &autocorrelator &narrow band &flexible &flexible &  \\
%Continuum & & &1GHz &1GHz &(old system)  \\
%Continuum & & &4GHz &4GHz &  \\
%\hline
%\end{tabular}
%\end{table*}


\subsubsection{Calibration Issues }
EMIR comes with a new calibration system. The external warm optics
provides ambient temperature loads and mirrors reflecting the beams
back onto the 15~K stage of the cryostat. This system is 
expected to be very reliable and constant over time. 
Absolute calibration accuracy will be better than 10\%  with EMIR
% with a midterm goal of $\sim5$\% 
when all details are well settled. 

Bands E\,150 and E\,230 have backshort tuned single--sideband mixers; 
DSB tuning is not possible, but sidebands (USB or LSB) may be selectable
within limitations. 
% the exception of the band  ends were one sideband is exclusive. 
The image rejection is better than 10 dB for all frequencies. 
On--site measurements of the rejection is not longer straightforward
for these mixers, since  the Martin--Puplett interferometers are not
 available anymore. As the optimum way of calibrating the image rejection  
is still under study, users who propose observations which rely
on an enhanced accuracy of calibration of image gains  
should mention this request in the proposal.

Bands E\,090 and E\,330 have tunerless sideband separation mixers, allowing
simultaneous observations of both sidebands in separate IF
bands. These mixers have been characterized 
in the laboratory for their image rejection and are expected to have
the same performance on site ($>13$ dB). 


\subsubsection{Velocity scales}

It is common practice at radio observatories to correct the frequency
of an observation for the strongly time variable velocity of
the Observatory with respect to the solar system barycenter. This
guarantees that lines observed near the Doppler--tracked frequency,
usually  the band center, always have the
correct barycentric velocity, independent of the time of
observation. However, the effect of the Observatory's motion on the
velocity {\it  scale} which affects most the velocity channels farthest
away from the Doppler--tracked frequency, is usually ignored. 

This effect which is of the order of $10^{-4}$ cannot be
neglected anymore if large bandwidths are used, as with EMIR. The
worst case occurs with band E\,090 where channels as far away as 20
GHz need to be considered 
%if the LO frequency is Doppler--tracked.
if a velocity channel in one of the sidebands is Doppler--tracked.
In unfavorable but nevertheless frequent cases (target source not too
far from the ecliptic, like the Galactic center), 
errors of up to  $\pm2$ MHz occur. 
Since the magnitude of the error changes with time, narrow spectral
lines may be broadened after a few hours of observation. 

Observers concerned by this complication may consult the 
\htmladdnormallink{30m web site}
{http://www.iram.es/IRAMES/mainWiki/EmirforAstronomers}
for further details and solutions.


%\subsubsection{Atmospheric Transmission }
%
%attachment:plot-iram30mv2.png \href{BR}{BR} Figure 1 shows the
%atmospheric transmission between 60 and 400 GHz for two precipitable
%water vapors, modeled with the ATM model.

\subsubsection{Update of PaKo}

The observer interface program PaKo has been adapted for
EMIR. In particular, the receiver and backend commands have been
 updated. The updated documentation will be available from the 30m web
 site in time for the preparation of observations with EMIR.



\subsubsection{Observation time estimator }


The GILDAS group  has prepared a new 30m time estimator for EMIR. It
is now part of 
the GILDAS software package and accessible via ASTRO. For downloading the
GILDAS package please connect to the
\htmladdnormallink{GILDAS home page}{http://www.iram.fr/IRAMFR/GILDAS/}
 and follow the instructions. A description of the new time estimator 
is also available on \htmladdnormallink{the Gildas web site}
{http://www.iram.fr/GENERAL/reports/}. \\
For HERA and MAMBO2, the old web based time estimator is
still available from the 
\htmladdnormallink{30m web site}{http://www.iram.es/IRAMES/obstime/time_estimator.html}.
Note that a web based version of the estimator for EMIR will be made
available %only 
for the next deadline.  As commissioning of EMIR has
not yet started at the time of writing, the new time
estimator is based on the laboratory performance of EMIR and the {\it
expected} losses at the telescope. 

