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The Hoot-Vega Radio Telescope



The Hoot-Vega Radio Telescope did not just happen. Its creation is the fusion of interests, inspirations, and support that goes back to my childhood. I have been a radio enthusiast for fifty-five years and amateur astronomer for more than fifty years. In some ways it is surprising that it has taken this long to fuse those interests together into this project. It still would not have happened without the generous support of my family and Dr. Eduardo Vega. Additionally, I want to acknowledge the hard work of the craftsmen whose efforts went into building the telescope. Special thanks go to Bruce Stevens and Jerry Grace, consummate craftsmen and easy working companions. Their many excellent suggestions have made the HRVT a better instrument than I had imagined. I would like to extend my thanks to these people and the others who have been there to support and encourage me during its development.

John E. Hoot
25 August 1999
San Clemente, CA

Postscript:  Sadly, Dr. Eduardo Vega pass away in 2003. His observatory and this instrument have gone through several ownership changes and, to the best of my knowledge, is no longer operational. I miss his enthusiasm and generous spirit.

Subsequent Developments

After about a year of design and development the HVRT tooks its first astronomical observations on August 21, 1999. Telescope commissioning observations and images are posted here. The formal dedication of the telescope and an introductory seminar on Radio Astronomy were presented at the HVRT site in early October of 1999..

Observation of Radio Sources 3C310 and 3C315

The first astronomical observations made with the HVRT were made as transit observations of extragalactic radio sources 3C310 and 3C315. These observations were performed with the following scope settings:

Gain = 20
Integration Time = 10 second
Sample Interval = 5 seconds
UTC Interval = 23:55Z 00:30Z
Declination = 26 degrees

This observation was made to determine the sensitivity of the instrument. According to the Cambridge Survey, the instrumental fluxes of 3C310 and 3C315 are 46.0 and 18.8 respectively. Below are two figures, the HVRT plot and a graphical representation of the same object taken at 1421MHz with the Bonn Radio Telescope. They are shown at approximately the same horizontal scale.

 

The strong correlation between these two figures, is compelling evidence that the HVRT has sufficient sensitivity to detect and image sources with Cambridges fluxes of 15 or more.

HVRT Overview

The HVRT is not a single radio telescope, but a collection of antennas, feeds, receivers, detectors and digitizers that can be used to make both geophysical and astronomical observations. It is more akin to a set of radio tinker-toys than to a single instrument. I will outline its primary configurations and uses, but do not let those constrain you. The HVRT can be configured to perform observations never envisioned by the author of this manual.

Physically, the HVRT is located in the Vega-Bray Observatory at the Skywatcher's Inn in Benson Arizona. The telescope is a complex instrument and needs to be run by a trained operator. Access to the instrument is controlled by the staff of Skywatcher's Inn.

The HVRT is composed of three different radio receiving systems.

  1. Steerable Microwave Receiving System configurable to receive at 1421 MHz, 4.0 GHz and 11 GHz.

  2. An omnidirectional integrating short-wave receiving system covering 0.5 MHz - 30.0 MHz

  3. A fixed 1691 MHz geostationary meteorological satellite receiving system.

Design Objectives

The HVRT was designed to meet several objectives and requirements. It is to act as a teaching instrument. It will be used routinely to demonstrate to observatory guests the function and purpose of radio telescopes.

  • To act as a test bed for exploring the capabilities of an modestly priced radio telescope

  • To be a test bed for remote radio observing

  • To operate as either a transit instrument or stare mode telescope

  • To provide all sky coverage

  • To provide a basis for expansion into an interferometer for high resolution observing.

The instrument that emerged from these requirements is summarized in the sections below. Each instrument group's function and major components are outlined. Detailed design descriptions for each instrument cluster can be found later in this manual.

Microwave Instruments

The microwave portion of the HVRT is divided roughly into a front-end subsystem and back end subsystem. The front end subsystem performs signal acquisition. The backend system decodes and analyzes the signals from the front-end system. The entirety of front-end system is located at the antenna site. It is connected to the backend system via a set of underground cables. The backend system is housed in the control room of the 20" telescope at the VBO.

The Front End Sub-System
The front-end system consists of the antenna, its positioners, feed horns, and RF amplifiers and down converters. The block diagram below depicts its major components.

The sections below describe the function of each of the components in the system.

Steerable 12 Foot Parabolic Reflector
The 12' parabolic reflector collects RF energy and focuses it at the feed point of the antenna. The antenna is mounted on a hitching post mount. This steerable mount allows the antenna to be pointed to nearly all sky locations. A heavy duty TVRO dish was adapted for use as the parabolic reflector. This was the most cost-effective way to obtain a dish with a figure good enough for use up to 11 GHz. For details on the pointing system, see the section on the antenna mount, and drive control system.

Feed Horns
Feed Horns are devices that collect radio energy at specific frequencies and direct it into cables or wave guides that in turn carry the energy to the electronic of the receivers.

Two different feed configurations will be supported. A 1421mhz L-Band feed with LNA and downconverter will typically be mounted on the system. This feed can be removed and replaced with a combined C and Ku band feed system covering 4 GHz and 11 GHz bands. It will collect C and Ku band TV signals, as well as C and Ku band radio astronomy signals. Mounting a different feed horn entails rotating the dish down and physically changing the component at the antenna focus.

Usage of the different feeds is summarized below:

Frequency

Usage

1421 MHz
3 degree resolution

Image Galactic
H-II regions (Orion, M16, ...)
Solar Observing
Milky Way

3700/4200 MHz
1 degree resolutiuon

Synchrotron Radiation
Pulars
Black Holes
Neutron Stars

11000 MHz
20 acr minute resolution (need dry days)

Synchrotron Radiation
Pulars
Black Holes
Neutron Stars

1420 MHz LNA
This is a low noise amplifier tuned to the emission frequency of neutral hydrogen. It amplifies the weak signal at the antenna to minimize signal loss in cables.

1420 MHz Downconverter
The downconverter translates the received signal from 1420 MHz down to 70 MHz. Moving the signal to a lower frequency simplifies the transmission, amplification and decoding of the signal.

C Band LNB
This low noise block down converter integrates an LNA and block down converter into a single device. It translates the signals in the range of 3.7 GHz to 4.2 GHz to 950 MHz to 1450 MHz. In addition this device has a signal polarization controller. This can be useful looking at polarized radio sources and is essential for decoding TVRO satellite signals.

Ku Band LNB
This low noise block down converter integrates an LNA and block down converter into a single device. It translates the signals in the range of 11.1 GHz to 11.6 GHz to 950 MHz to 1450 MHz. In addition this device has a signal polarization controller. This can be useful looking at polarized radio sources and is essential for decoding TVRO satellite signals.

Back End Sub-System
The backend system contains the primary operator control point for the telescope and performs all the signal processing and decoding. A block diagram of the major components is shown below:

The back end sub systems contains the following major components:

BSR1100 Receiver
This is an off the shelf C/Ku band satellite receiver. It was selected for its moderate cost, variable bandwidth, 70 MHz IF frequency and ease of modification. The receiver performs dual duty. It will receive and decode standard TVRO signals when the telescope is used as a TV receiver. It can also be used as the Ku and C band receiver for radio telescope when the modifications are enabled.

The receiver is modified to include an external RF gain control. This disables the automatic gain control system used when receiving TV with the unit. A tap will be made to the 70 MHz IF to bring this signal out where it can be fed to the radio telescope 70 MHz backend.

70 MHz Backend
The 70 MHz backend contains RF amplification, a wide bandwidth product detector and analog to digital converter with adjustable gain and integration time constants. It conditions the received signals for the computer.

Antenna Mount Controller
The antenna mount controller allows the user or computer to point the antenna at various parts of the sky. For details on this device, see the associated white paper.

The Short-wave Monitoring System
The short-wave monitoring system is used for geomagnetic and solar flux sensing. It may also be adapted to meteor scatter observing. It consists of the following main component:

  • Fiberglass exterior whip antenna

  • RG58 Feed Line

  • AC/DC LW-MW-SW-FM receiver

  • Signal Integrator

  • Digital Oscilloscope & Chart Recorder

The digital oscilloscope and chart recorder offer the ability to digitize signal characteristics over long periods of time and is useful for the general maintenance and calibration of the system. Facsimiles of the operating documents for these items can be found in the appendices to this manual.

The Weather Satellite Imaging System
The weather imaging system consists of a 1 meter dish, feed horn, LNB, scanning satellite receiver, decoder, computer system and software. This system runs continuously, downloading imagery and displaying it on an NTSC video monitor with the ability to transmit this imagery over short distances with a low power TV transmitter. This system allows remote earth observation and the creation of dynamic video loops.

The Computer Systems
There are two separate computers at the site. One computer is dedicated to the Meteorological Satellite receiving system. It is an older 286 PC running MS-DOS 5.0. It is dedicated to the continuous reception of weather satellite imagery that is presented on a TV monitor at the work station and broadcast over a short haul radio link for reception in the media room of The Inn.

The other computer is the primary control and data acquisition computer for the microwave and short-wave instruments. It can be operated from the operator's position or can be controlled by a remote user

The primary computer's function's include:

  • Data Acquisition

  • Power Control for the Instrument Racks

  • Position the Microwave Receiving Antenna

  • Digitizing Radio Signals

  • Analyzing and Presenting Data

  • Locating Objects From Catalogs

  • Sky Map Presentation

  • Remote User Support

  • Remote User Verification

The primary computer is currently an IBM Compatible PC running Microsoft Windows 95. The present configuration includes:

  • 486DX25 CPU

  • 8 Meg RAM

  • 210 Meg Hard Disk

  • 4 serial ports

  • 2 Parallel Ports

  • Mouse

  • CD-ROM

  • 3.5" 1.4Meg Floppy Disk

  • External 56K BPS Modem

  • 101 Key Keyboard

  • SVGA Monitor

The relatively modest computing power of this system is adequate to its purpose. As more powerful machines become cheaply available, it will undoubtedly be upgraded.

The computer will be configured to concurrently run several different programs:

HVRT Control Program
This is a Windows based program that acts as the central control point for the telescope. It handles pointing, data acquisition, unattended operation, data reduction and analysis. It allows you to point the telescope to a specific RA/DEC, ALT/AZ, catalog object, Meridian Transit position or Geostationary satellte location. The program will digitize data from the 70 MHz backend receiver. This information may be displayed graphically on the display and/or saved as a stream of position and flux readings to ASCII text log files for subsequent analysis. The program will create FITS files from the flux observations.

Scope-It
Digital Data Recorder programs for the PC to store the output from the 70 MHz telescope backend and from the short-wave monitoring system. It includes a FFT (Fast Fourier Transform) mode for pulsar period measurement and a long duration chart recorder useful for timing pulsars.

FitsView
This is a freeware program from the NRAO. It allows you display and manipulate FITs format images. It is invoked directly from within the HVRT Control Program

SK2000
A planetarium program customized to feature the CAMBRIDGE 3Cxx catalog of celestial radio sources. This will allow you to pick objects to view and calculate their current positions.

Hidden Image
A program to perform maximum entropy deconvolution on FITS files. The idea here is that if we can exactly calibrate the antenna pattern (equivalent of the optical PSF) we can get a 3x or 4x improvement in resolution in our images by using Maximum entropy deconvolution on our images. This will yield 15 arc minute resolution at 4 GHz and 5 arc minute resolution at 11 GHz.

PC-Anywhere
This commercial program allows remote users, connected via a modem or over the Internet to control the telescope computer as though they were at the console. Additionally, it provides a fast file upload and download facility to allow remote users to retrieve their data files.

 


SSC Observatories Offices:
1303 S. Ola Vista
San Clemente, CA 92682
Email: observatory <at> ssccorp.com




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