Amiga Computing - Commodore Is Awesome

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•
ODRELL Bank is the place to be if
you're into radio astronomy. I
went there, just off the MO at junction
18, as a visiting student partly
because I was interested in the image
processing that's involved in making
all those pretty, false-colour piccies
that Patrick Moore gets so excited
about.
"Basically, we run a VAX cluster",
said Paul Harrison as we walked into
the terminal room, "but there's all
sorts of other machines tied into it.
We've got terminals left over from
Systime days. About half are text only
most are monochrome. Over here are
our two graphics work stations...."
I missed what he said next, because
over on the bench, looking battered and
well worn, was the familiar form of a
lowly A500, and sitting next to it was a
huge 1024 pixels by 740 Ikon monitor
with a false-colour Quasar on its screen.
Both light and radio waves form
part of the electromagnetic spectrum,
differing only in their wavelength and
frequency. With the naked eye,
we can see only in the "optical"
wavelengths, though many
Insects can see in ultra-violet
and infra-red.
Going up in frequency (and
down in wavelength) from the visible
you have ultra-violet rays, X-rays and
Gamma rays. Going down in
frequency (and up in wavelength) you
get radio waves.
The advantage of looking at things
in the radio wavelengths is that the
waves pass more easily through dust
than light, making objects easier to
detect. You can also tell what atoms
make up the object, and basically
"see" in greater detail than with
optical telescopes.
Enough of all that. You want to
know about computers, so I'll tell you
about computers. Like all science in
this country, Jodrell is incredibly
under-funded. As a result they work
to an "if it works keep irphilosophy.
T
telescope (Mk la) is still used
with H the original 1955 analogue
computer, A though the hard work is
now T done with a digital machine. But
it mworks:
The motors driving the dials
on e the front have to be replaced more
often
a
than the valves that glow away
to themselves in the heart of the
machine. n
s In those days astronomy was a
t
h
a
graph paper and ruler affair.
Nowadays most astronomers would
give up without at least a Vax to work
with.
Why the change? Well the bigger the
telescope, the finer the resolution. To
the Mk la, the quasar I first saw was
nothing but a point. And that
telescope is just about as big as you
can get - even so gravity stretches the
telescope bowl enough to affect its
performance.
The way to get round this is to tie
two telescopes together using a
Earth
Iii
As Jodrell Bank has
been keeping an eye
on the universe, an
Amiga has been
keeping an eye on it.
Joe Garner
investigates how an
A500 has become an
interstellar graphics
terminal
FEATURE MI
technique called Interferometry to
simulate a telescope as wide as the
"base line" - the distance between
them.
Before computers came along you
couldn't use more than two telescopes
to do this, and even then the results
would be meaningless to me and you.
In Britain we have a Interferometer
stretching (by the time of publication)
from Cambridge to West of Jodrell.
This simulates a telescope hundreds
of kilometers across. The network is
called Merlin (it really does stand for
something) and I've been told that the
Mk la controlling computer is called
Arthur because it's Merlin's friend. I
think the real reason has something to
do with The Hitch-hiker's Guide To
The Galaxy...
When Merlin was designed in the
mid '70s there were no suitable
computers in the world to control all
the telescopes and bring the data
together. So Jodrell built their own,
called Circes.
They have no proper
1111 microprocessors - the CPU
is a circuit board, not a
chip. The most complicated
e s h i r e component adding chip. on You it is enter: an
program by selecting an address on
finger-wheels, and then flicking in the
binary on a bank of switches. The
control program was written in Forth
and then compiled.
The Micro-Circes are still in place,
the only change being to replace the
paper-tape reader with aproms. Each
out-station (remote telescope) is
controlled by a Micro-Circe which
takes commands from Jodrell. The
received signal from the telescope is
sent back via a microwave link,
cooled as near to absolute zero as
possible to avoid adding noise.
N you're looking for a signal
Othat's
10,000 times weaker than the
Ibackground
noise. This is where the
Sfirst
piece of really clever hardware
E comes in (these telescopes are just
i
souped-up radios).
A new version is being built to
s
accommodate the latest telescope, at
iCambridge,
add extra channels, and
mimprove
the data by about 20 per
pcent.
It works like this:
o The analogue signal is converted
rinto
a two bit binary number between
t
a
n
t
AMIGA COMPUTING November 1990 65