Background

The SRT (www.haystack.edu/edu/undergrad/srt/index.html) was first developed by the MIT Haystack Observatory as a teaching device capable of performing L-Band (1.42 GHz) continuum and spectral line observations. The dish is a standard satellite TV dish using an Az/El mount designed by the CASSI Corporation (www.cassicorp.com) and operated by a BASIC Stamp microcontroller. There are currently over 80 systems in use worldwide.

The original system consisted of two main components; a commercial TV satellite dish and a small book-sized control box. Users interfaced with the system through a Java applet with limited functionality and display. Starting in 2002, the University of Iowa began a process to enhance their SRT system. An inclinometer and optical encoder were added to the elevation and azimuth dish axes and used to determine the absolute position. In 2004, the signal processing function of the control box was bypassed and routed through a more “hands-on” super-heterodyne receiver with adjustable local oscillators (LO’s), amplifiers, filters and mixers. A 1024 channel autocorrelator was also developed to add sensitivity and resolution. Starting in the summer of 2006, a Labview interface was added which now controls both the motion of the radio dish as well as the operation of the autocorrelator.  The major modifications to the new eSRT system are highlighted below.

Modifications

Inclinometer and Azimuth Encoder

To aid in pointing, a Smart Tools Technologies (www.smarttooltech.com) inclinometer and US Digital (www.usdigital.com) absolute optical encoder were added to the dish axes. The eSRT is now no longer required to return to the home position before operation or periodically during operation for pointing accuracy.

Inclinometer Encoder

RF Receiver System

University of Iowa eSRT system The eSRT signal processing has been expanded to a 3 stage, super-heterodyne receiver system. Each stage is fully accessible to the end-user and test points have been inserted at various locations along the signal path to allow viewing of the heterodyne and amplification process.  The new system also contains an In-line noise diode and Ultra Low Noise Amplifier (ULNA).  A block diagram of the system is shown below.

Block 1 Block 2

For more information on building an RF receiver, check out the PPT presentation below:
Building a Super-Heterodyne Receiver.ppt

Autocorrelator

To record the radio spectrum, a 1024 channel (50 MHz Bandwidth) correlator was developed. 

Autocorrelator

Labview Interface

The original SRT Java interface has been replaced by a modular control system developed in National Instrument’s (www.ni.com) Labview 8.0. The e-SRT hardware is controlled by Labview Virtual Instruments (VI’s) which are fully accessible to the telescope user and can be modified to accommodate hardware changes and/or upgrades. With the new interface users can position the dish by dragging a cursor on the main display, view a map in either Az/El or Galactic coordinates, or schedule observations for multiple positions. Observation data is saved in the form of ASCII data files which can be further evaluated by the user offline.

screenshot

For those interested in developing an enhanced SRT of their own, we are freely distributing our Labview interface.  The most recent version of the interface includes a demo mode to help incorporate hardware changes.  The current version of the Labview interface can be downloaded here.
eSRT.zip

Results

The eSRT is used primarily as a teaching tool for graduate and undergraduate courses. A few past experiments have included: