The Zpectrometer is an ultra-wideband spectrometer for the NRAO Green Bank Telescope.   Below you will find
A brief paper describing the Zpectrometer and its science goals appeared in the Proceedings of a workshop held at the North American ALMA Science Center in 2006 is available here.  More information is available below.

Recent news

The input hybrid on the Ka-band receiver has been changed to a 90 degree hybrid, with reduced receiver temperature and increased bandwidth.  The Zpectrometer system was released for general observations in late October 2010.


Images and descriptions

The Zpectrometer at the 100-meter diameter Green Bank Telescope (GBT) will produce ultra-wideband spectra to search for distant galaxies, such as this simulation of observations of the CO J = 1-0 line over redshifts of 1.9 to 3.4.   This project is funded by the National Science Foundation's Advanced Technology and Instrumentation program from 2005-2008.  The proposal  abstract (pdf)  contains the project goals.  The spectrometer uses WASP2 analog lag correlators attached to the GBT's Ka-band correlation receiver.  Some of the important aspects of multi-channel correlation spectroscopy are summarized here in a brief paper (pdf, ps) titled Spectroscopy with Multichannel Correlation Radiometers.

doubled WASP

Minimalist design view of correlator dual-band chassis design with 16 correlator cards, power splitters to feed the cards (below cards), separate downconverter and amplifier modules to both sides, control computer, and phase switch drive card.

Zpectrometer in the lab

The Zpectrometer in the lab at Maryland.  From top to bottom, the chassis are the power supply, two correlators, the IF distribution box, and two further correlators; network hubs and fiber conversion boxes are at the very bottom.   The  enclosure, designed and fabricated by NRAO Green Bank, is an effective RF shield when the front door is closed.  Putting the wheels on outriggers adds stability and allows the enclosure to roll through standard height doors.  All of the cables attach to the individual chassis' front panels to simplify the enclosure design (at the cost of adding some clutter when the enclosure is open).

zpect on gbt
The Zpectrometer hangs on the GBT's receiver turret next to the Ka-band front-end, which is just visible to the right.

zpect on turret

In operation the Zpectrometer is completely enclosed in its shielded rack.  The bottom of the Ka-band receiver and its Caltech Continuum backend are clearly visible in this view.

The top of the receiver turret carries the feed horns for the GBT.  The Ka-band feeds are under the white cover that is the furthest to the left in this image.  A set of hoses blows warmed air across the covers to keep them dry.

The receivers seem to hang from the ceiling in the receiver room; they're actually on a large rotating "turret" that selects which one is at the telescope focus.  The Ka-band receiver is just above the ladder.

A good view of the Ka-band receiver electronics.  The warm microwave electronics are on the aluminum plates.  It is easy to recognize the micrometers for phase and amplitude adjusters for both channels of both polarizations.

Here is a closeup of the bottom of the Ka-band receiver cryostat.

inside the cryostat

Galen, the receiver engineer, looks at the receiver innards.  Although normally cooled to 20 K, this lab photo (courtesy H. Li) shows the receiver cryostat open and warm in the lab during an earlier visit.  From top to bottom, one can see the feed horns, transition sections, orthomode transducers that separate the polarizations, cross-guide couplers for injecting calibration signals, and the magic tee 180 degree hybrids.  The amplifiers are off for testing.  Other pictures of the inside of the cryostat are available in the NRAO pages.

A WASP2 spectrometer in the Green Bank RF anechoic chamber to measure its radio and microwave emissions.   The room itself is a metal box with walls covered in blue RF-absorbing material.


Concentrating on the spectrum analyzer display that shows the emission spectrum from the spectrometer.

Questions or comments?  Please contact Andrew Harris.