26-meter West Radio Telescope
The AntennaBoth 26-m radio telescopes point and track at sidereal or user-defined rates for astronomical observations. The control system is built by DFM Engineering, Inc. The 26-m radio telescopes use position encoders with 18-bit resolution and the addition of dual 15 HP computer controlled synchro motors on each axis. PARI has conducted pointing model measurements to ensure pointing accuracy to within a fraction of a beamwidth.
We have five scanning spectrometers and two 64 Msps FFT spectrometers.
- The scanning spectrometers are 15kHz filter bandwidth with +/-2 MHz maximum scan range around a 70 MHz center frequency. Integration times are 0.3, 1, or 10 seconds in either continuum or spectrum mode. Sweep width can be narrowed around the predicted shift frequency. Rest frequency correction is available to recenter the few kHz error in the 1420.405 MHz to 70.00 MHz downconversion.
- The 66 Msps spectrometer [ SDR-14 www.rfspace.com ] has a variety of modes that allow input frequencies in nyquist mode at 0-30 MHz input or 0-230 MHz in undersampled downconversion mode. We normally use it with an Icom R8500 receiver as the front end downconverter. This radio's IF is 10.7 MHz with several MHz of bandwidth for input to the SDR-14. This part of the system also is used for interference resolution. The receiver has been modified to allow external referencing to our GPS time/frequency system or our Rubidium standard. This allows more spectral resolution than we need (sub-Hz) with FFT sizes from 2048 to 262,144 point. The spectrometer also has a realtime mode that allows lossless recording of a 140 kHz portion of any frequency range direct to hard drive. This allows later post processing or evaluation of the spectrum in the time or frequency domain since it is stored in complex I-Q format.
- The second 64 Msps spectrometer is called a Universal Software Radio Peripheral (USRP) [ http://comsec.com/wiki?UniversalSoftwareRadioPeripheral ]. This spectrometer is a flexible platform for software development. It contains multiple channels of 12-bit digitization and a Field Programmable Gate Array (FPGA) to provide fast on-board manipulation of data as required. This will allow interferometry and pulsar signal processing algorithms to be accomplished directly in the USRP instead of inside a much slower PC.
Most downconversion on site is currently crystal controlled and not referenced to 10 MHz. In critical applications we have used PTS-160 synthesizers to substitute for crystal oscillators. That also allows locking to the 10 MHz reference. The east 26m antenna is currently set up at 327 MHz for Pulsar research. Dr. David Moffet at Furman University is the PI on that effort. This is the only frequency that has both polarizations instrumented currently. System noise temperature is around 50K.
Most of the frequencies are downconverted to 1.1 GHz or 1.4 GHz IFs in the feed box and then routed down the antenna. We are able to downconvert to 70MHz in most cases under the antenna before going across the site to the control room.
Current receivers on the West 26-m telescope
include the frequencies 1.4 GHz for HI measurements, 4.8 GHz for
formaldehyde. The 26-m radio telescopes can also be used at other
frequencies with receivers provided by visiting astronomers.
Raster scan map of Virgo A taken at 1420 MHz using 26W. The image is one degree on a side.
radio bright source Virgo A was mapped at 1420 MHz (right) using the
PARI 26-m West radio telescope. The map was made August 30, 2001 UT by
raster scanning at intervals of 6 arcminutes covering a total area of
one degree by one degree in RA and Dec. The axes of the base of the
surface plot are in units of 6 arcminutes. The flux is in ADUs. The
calibrated flux of Virgo A is 1000 Jy, so 1 ADU is about 1 Jy. This map
was made as a test of the mapping capabilities of 26-W. The 26-m East
radio telescope has the same ability to map. Also, both radio
telescopes can work together to map a source.
Since radio astronomy observations have been driven toward higher frequencies, PARI has made additional modifications and enhancements to the antennae that will expand their capabilities for astronomical use over a wide range of frequencies.
PARI 26-m West Radio Telescope. Current radiometers on the West
26-m telescope include the frequencies 1.4 GHz for HI measurements, 4.8
GHz for formaldehyde. The 26-m radio telescopes can also be used
at these frequencies but require an external research project
to make available the respective radiometers.