Purpose

Overview

Click on the following for a short summary and recent updates:

• A-band (e.g. 230 GHz)
• B-band Array (HARP) (e.g. 345 GHz)
• B-band (e.g. 345 GHz)
• D-band (e.g. 690 GHz)
• ACSIS (spectrometer backend to the above)

Questions should be directed to the undersigned.

This receiver provides spectral coverage from about 211 to 279GHz, the lowest frequency band in which the JCMT operates for spectral line observations. The extreme frequencies can be reached with a suitable choice of sideband. A3 has a single channel with a low-noise SIS mixer having a typical noise temperature Trec(DSB) of about 70K over most of its range. A hump in the noise temperatures occurs between local oscillator frequencies of 245 and 260 GHz, which makes it difficult to calibrate data near this frequency range. For a fuller discussion of this problem, click here. Although A3 does not have a single-sideband filter, one can minimize the side-effects of this feature for almost all common spectral lines with a suitable choice of sideband. Note, however that the sideband ratio is not unity within the entire tuning range of this receiver, especially near this "hump"; see results of tests using HC₃N lines. For further information, see the A3 Web pages and the Guide to Spectral Line Observing at the JCMT.

Current Status

RxA is used extensively in bad weather with good results. For the most part it is behaving reliably, although we have been experiencing some tuning problems below about 217 GHz.

Anticipated for semester 07B

RxA will be available for observing in semester 08A, although we will be monitoring the noise "hump" for further changes.

HARP is a 16-element B-band array receiver operating from 325 to 375 GHz. The receptors are arranged in a 4x4 grid, separated by 30" (approximately 2 beamwidths).

Current Status

HARP is used extensively, mostly with good results. Of the 16 receptors 14 are currently operational. The non operational receptors are number receptor 4 (H03) and receptor 15 (H014). Receptor 4 is at a corner and receptor 15 on the edge. Note that receptor 4 not is producing any data (masked out) while 15 still produces data but of doubtful quality due to oscillations.

Anticipated for semester 08B

HARP will be available for observing in semester 08B.

In early 2007 two B-band mixers, using spare junctions from HARP and new mixer blocks manufactured under the umbrella of the eSMA development, was installed in RxW. Its tuning range will be slightly greater than that of HARP, approximately 315 to 375 GHz, although it, like RxW(D), must be tuned manually. The primary function of the receiver will be as part of the eSMA interferometer, but, once commissioned, will be available as a single-pixel, dual polarization receiver for single dish observing. Applicants should note that once HARP on-array chopping is commissioned, HARP's sensitivity to compact sources will be the same as for RxW(B). This assumes that the HARP mixers in RxW(B) will have the same noise temperature as in HARP.

Current Status

Both mixers in RxW(B) are working but the receiver is not yet re-commissioned. From  testing the receiver noise temperature is twice of the HARP value. Investigation ongoing why this is the case.

Anticipated for semester 08A

As with HARP, sensitivities are anticipated to be significantly better than with RxB3. Applicants may propose to use RxW(B) in semester 08A, with the caveat that if the current sensitivity not is improved HARP will be superior.

This receiver has two mixers with opposite polarization for use over the 630-710 GHz region). The D-band mixers have tunerless (non-adjustable) backshorts, and usually operated in single-sideband mode. In early 2007 RxW(D) was upgraded by using spare junctions provided by SRON from their ALMA Band-9 development project. Lab testing indicates that the new parts can improve system temperatures by more than 30%.

Historically, the D-band mixers have a DSB Trec of typically 350-450K at midband. Receiver temperatures (see D-band plot of SSB values here) were surveyed in August 2001; at 660 and 691 GHz the DSB values for channels A/B were 317/376 and 441/372 K respectively. More information of the historical performance of RxW can be found in the on the old Receiver W Web pages.

Current Status

The new mixers were installed in February 2007 and appeared to work. However, the mixers could not be tested due to a LO problem. The LO has been repaired. However, in the mean time one mixer appears to have gone open circuit. Discussion are ongoing with SRON about repairing the mixer. Thus commissioning has only just started.

Anticipated for semester 08A

Expectations is that the sensitivity will be improved by 30% due to the improved mixers. However, similar expectation for RxW(B) has so far not been realized. Further, even if the commissioning is completed in the fall of 2007 it is unclear when the second mixer can be repaired and installed.

The ACSIS correlating spectrometer is a highly flexible backend designed to work with HARP, but which works with all our receivers. Please see www.jach.hawaii.edu/JCMT/spectral_line/Backends/acsis/acsis-guide.html for a list of available bandwidths, spectral resolutions and backend modes.