It was Einstein who made the real trouble. He announced in 1905 that there was no
such thing as absolute rest. After that there never was.
-- Steven Leacock
The radio telescope includes the following components:
- 10' Parabolic Antenna (Satellite
Dish): The antenna
collects the radiation. The dish is a standard satellite TV dish ten feet in diameter
or 3.042 meters. The antenna has an aluminum mesh surface and is mounted to a single
drive motor that has limited range of movement. The dish has been installed adjacent
to the Randolph-Macon Keeble observatory.
- A/D Down Converter: The signal collected
from the feedhorn is an analog signal, so for the receiver to recognize the data
it must be converted to a digital signal. The signal entering the down-converter
is the already amplified 1420 MHz signal. The output is a 70 MHz signal that then
goes into the lab to the receiver.
- Attenuator: This is used to decrease the
amplitude of the signal before it enters the receiver. This is useful when the front-end
devices have too much gain. Also, if the gain is too high the receiver's electronics
do not function within the log scale and so become inaccurate.
-Computer Interface: The computer is a relatively
basic setup. The receiver connects to the computer through a serial port and is
interfaced by software provided by the manufacturer. Data is taken through the software,
saved and accessible later. Typically, we then import the text into another program,
where it is then plotted and analyzed.
-Feedhorn: The feedhorn is the collector located
at the focus of the antenna. This then connects to the amplifier.
-Noise Source:This is used to test the output
of the receiver to the computer. The noise source provides a known strong signal
that allows calibration of the output of the receiver. This allows adjustments to
be made to the IF Gain or DC gain to put the signal within the limits of the software.
- Power/Signal Cables: The cables from and
to the dish include power cables for the LNA, drive motor and signal preamp. These
cables run through conduit to a laboratory on the second floor of the Copley Science
building. Low loss coax cable connects the feedhorn to the down-converter and then
inside to the receiver.
-Pre-Amp LNA: Also known as an LNA or (low
noise amplifier). The signal collected by the feedhorn is naturally weak (with any
size antenna), so the signal is amplified before it reaches the cables and ultimately
- Receiver:The receiver operates at 70 MHz,
the down-converted signal. This ultimately allows us to observe the
Hydrogen 21 cm emission line created by the ground-state "spin-flip" in
neutral atomic hydrogen.
The Feedhorn, A/D converter,
Pre-Amp, and Receiver can be seen here
-Drive Controllers: These allow us to remotely
maneuver the dish into a desired Alt. Az. direction. The controllers are programmable
allowing presets to made for the limits of movement and zenith direction. They are
operated independently, but can operate simultaneously.