Click here to see the working
pictures of Radio Astronomy Telescope
We make it happen
We are
about to embark on building a short-wave receiver
which will pick up radio signals from the planet
Jupiter and also from the Sun. This receiver
containing over 100 electronic components and piece of
hardware. Fabrication will include the handling of
small, delicate, electronic parts, most of which will
be mounted and soldered on a printed circuit (PC)
board.
Theory of Operation
Radio
signals from Jupiter are very weak—they produce less
than a millionth of a volt (1 microvolt, 1µV) at the
antenna terminal of the receiver. These weak radio
frequency (RF) signals will be amplified by the
receiver and converted to audio signals of sufficient
strength to drive headphones or a loudspeaker. The
receiver also serve a narrow filter, tuned to a
specific frequency to hear Jupiter while at the same
time blocking out strong earth based radio stations on
other frequencies. The receiver and its accompanying
antenna are designed to operate over a
narrow
range of short-wave frequencies centered on 20.1 MHZ
(megahertz). This frequency range is optimum for
hearing Jupiter signals.
Antenna
The
antenna intercepts weak electromagnetic waves which
have traveled some 500 million miles from Jupiter to
the Earth. When these electromagnetic waves strike the
wire antenna, a tiny RF Voltage is developed at the
antenna terminals. Signals from the antenna are
delivered to the antenna terminals of the receiver by
a coaxial transmission line.
Radio Frequency Filter and
Preamplifier
Signals
from the antenna are filtered to reject strong
out-of-band interference and are then amplified using
a junction field effect transistor (JFET). This
transistor and its associated circuitry provide
additional filtering and amplify incoming signals by a
factor of 10. The receiver input circuit is designed
to efficiently transfer power from the antenna to the
receiver while developing a minimum of noise within
the receiver itself.
Local
Oscillator and Mixer
The
local Oscillator (LO) and mixer perform the important
task of converting the desired radio frequency signals
down to the range of audio frequencies. the local
oscillator generates a sinusoidal voltage wave from at
a frequency in the vicinity of 20.1 MHz. The exact
frequency is set by the front panel tuning control.
Both the amplified RF signal from the antenna and the
LO frequency are fed into the mixer. The mixer
develops a new signal which is the arithmetic
difference between the LO and the incoming signal
frequency. Suppose the desired signal is 20.101 MHz
and the LO is tuned to 20.100 MHz. The difference
frequency is therefore 20.101-20.100 = .001 MHz, which
is the audio frequency if 1 kilohertz. If a signal
were at 20.110 MHz, it would be converted to an audio,
the radio is know as a direct conversion receiver.
Low Pass Filter
To
eliminate interfering stations at nearby frequencies,
we use a filter which is like a window a few kilohertz
wide through which Jupiter signals can enter. When
listening for Jupiter or the Sun, the radio will be
tuned to find a "Clear Channel". Since frequencies
more than a few kilohertz away from the center
frequency may contain interfering signals, these
higher frequencies must be eliminated. This is the
purpose of the low pass filter following the mixer. It
passes low (Audio) frequencies up to about 3.5 KHz and
attenuates higher frequencies.
Audio Amplifiers
The
purpose of the audio amplifier following the low-pass
filter is to take the very weak audio signal from the
mixer and amplify it enough to drive headphones
directly, or to drive an external amplified speaker
assembly.
(Figure
Courtesy: Amrut.Yalagi, Secretary)
What is the
need for Radio Astronomy?
There are certain
wavelengths that would not be visible from the earth's
surface because of the atmosphere. Since our
eyes are limited to the optical regime we have to use
other means of detecting.
Where Radio waves come from?
Many objects in the
universe emit radio waves.
The
"view" of an object as seen in the radio wave region
can be quite different from what is seen in the
visible light region.
Basics of Radio Astronomy:-
Wave basics –
electromagnetic radiation
electromagnetic spectrum
Astronomy basics – co-ordinate system, time, Doppler
motion, and source velocity.
What are the differences
between Radio and Optical Astronomy?
Design of the instruments
Resulting data
that is found
Different sources that are seen.
So
exactly, What is Radio Astronomy?
Radio astronomy is the
study of the Universe in the radio part of the
electromagnetic spectrum.
The radio spectrum ranges from approximately 1mm to 30
meters
Almost all of it accessible from ground-based
observatories, day and night.
A partial list of Astronomical objects detected at
Radio Wavelengths:
Milky Way emissions
Radio Galaxies
Quasars
Pulsars
Cosmic Back ground radiation
Atomic Hydrogen emission
Molecular clouds
Radio Astronomy in
TPSY?
More shortly in the
near future our society is going to have its
first laboratory.
The laboratory will
be based on Radio astronomy
What do we do in
TPSY?
Studying the Jovian
system
As well as the Sun emissions
TPSY Radio
Astronomy Lab: -
Operates at 20MHz
and will have:
Radio Jove includes,
Antenna
Receiver
Dish
Software's
If you have any
questions regarding Radio Astronomy then please
mail them at:-
radio_astronomy@youthplanetary.org
