Amiga Computing - Commodore Is Awesome

m 0 .5
A
70
,
0 and 3_ The signal then passes on to
-a
bank of 128 custom chips under the
control of a 68010. Slightly different
signals are combined once in each
chip, read out by the 68010,
recombined into a single value and
stored in delay memory.
Each combination of two telescopes
has a board like this, and the signals
from each board must arrive at the
same time. Some telescopes are
nearer to Jodrell than others, and so
signals which arrive at the same time
at each telescope arrive at different
times hack at Jodrell.
All this is synchronised by a
master 68010 board that collects all
the signals in step and stores it in ram
until it's needed. The reason this
process is so clever is that because
noise is random and the true signal is
constant, by combining the signal lots
of times, the random noise will cancel
itself out.
On average, pure random noise will
fluctuate evenly between positive and
negative limits, so that if you take
enough samples it will add up to zero.
As a result you remove noise and
amplify the required signal. The two
bit number does not affect the final
value because, again, the average
signal strength will be a multi-bit
number.
To see what I mean, here's a very
PLOT FILE VERSION 1 CREATED 08-AUO-1g90
V VS U FOR 3C120-MERLN.VCALXY.1
ANTENNAS ** - ** C O R R LL
1.5 I I .1
1.0 -
A
V 0 . 0
-0.5
-1
.0
(--
•
14:00:29
_
-1.5 • • • • .• •
-1.5 - 1 . 0 - 0 . 5 0 . 0 0 . 5
MEGA RAVLNUTM
58 AMIGA COMPUTING November 1990
4
The Amiga makes
the other equipment
look over priced
over-simplified for instance. Imagine
you were timing how long it took a
stone to drop 22.5 metres and it took
1.5 seconds. Fine, but what if your
clock could only measure 1 or 2
seconds?
Well if you took lots and lots of
readings, after a while 50 per cent
would be 1 and 50 per cent would be
2, which averages out at 1.5. If you
still don't get it, don't worry: The guy
who's building the thing doesn't quite
1.0 1 . 5
This is the
raw data
from the
telescopes.
After
cleaning-up
it looks a
lot prettier
Hi there! My name
is Eddie and 1 Just
know we're going
to get on fine...
know what's going on either. rust
remember, there are about thirty
680108 running in parallel there, so it
must be good.
The results are read out by another
Circe, which is due for replacement
by a VAX in a month or so. This first
stage is about 94 to 98 per cent
efficient. The data is usually dumped
on to mag tape before processing.
I two telexes and two terminals on a
phone N link to Manchester. Data was
erased 1 whenever disk space was
needed, 9 there were no graphics
terminals
7
and everyone was tearing
their hair out and jumping up and
down. 7
eThen
came a Systime
minicomputer-cum-mainframe. v
A
little e later it was replaced by a VAX
that r took up a decent room-sized
room. y That was replaced by a VAX
3400
t
mainframe the size of a couple
of suitcases. Now the VAX cluster
contains h half a dozen machines. Online
i disk space is over 2500 Mb.
nStorage
is on disk, hard disk, video
disk, g video tape and mag tape for
transportability. w
On-line VAX memory
is
a
around 200 Mb.
s
Before! go on about the hardware
any
r
more. I'll tell you what it needs to
do. The swirly graph is a picture of
the
u
track each telescope pair traces
across n the sky (the receiving areas of
each f telescope are just overlapped on
the r same area of sky, so that the
o
m