Hi guys,

I saw the Australian movie, "The Dish" over the holidays. It's about the
Parkes Observatory and the large dish antenna used to relay video, audio,
and telemetry feeds from Apollo 11 in 1969 back to NASA.

At one point in the movie, they lose track of where Apollo 11 is and have to
scramble to manually point the dish to get a signal again. However, once
they DO manage to get a signal, they flip a switch and the dish continues to
automatically track Apollo 11.

I'm curious... how is this down? 3 or 4 slightly offset (from the dish's
central feedpoint) receivers, the outputs of which are compared to determine
which way the transmitting source is 'drifting' (then feed back to the
motion control system to move the dish that way)? Or is there a simpler
means?

Thanks,
---Joel Kolstad

On Wed, 5 Jan 2005 12:15:33 -0800, Joel Kolstad wrote:
Hi guys,

I saw the Australian movie, "The Dish" over the holidays. It's about the
Parkes Observatory and the large dish antenna used to relay video, audio,
and telemetry feeds from Apollo 11 in 1969 back to NASA.

At one point in the movie, they lose track of where Apollo 11 is and have to
scramble to manually point the dish to get a signal again. However, once
they DO manage to get a signal, they flip a switch and the dish continues to
automatically track Apollo 11.

I'm curious... how is this down?

By counting on the gulibility and limited education of movie audiences. :-)

3 or 4 slightly offset (from the dish's
central feedpoint) receivers, the outputs of which are compared to determine
which way the transmitting source is 'drifting' (then feed back to the
motion control system to move the dish that way)? Or is there a simpler
means?

The way a Hughes Radar system I once worked on did it was to spin the
horn in the dish focal point. The horn was E V E R S O S L I G H T L Y
off center in its axial alignment. The receive signal strength was
constantly compared against a servo feedback from the horn assy. to
determine which way (what angle) the signal source was drifting.

In a system that was polarization sensitive, I guess one could "joggle"
the position of the horn assy. and achieve much the same results.

HNY
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | linux
| Gunnison, Colorado | @ | Jonesy | OS/2 __
| 7,703' -- 2,345m | config.com | DM68mn SK

On Wed, 5 Jan 2005 12:15:33 -0800, "Joel Kolstad"
wrote:

I'm curious... how is this down?

Hi Joel,

This may not answer your question, but you can always contact the
author of:

To: "Richard Clark"
Subject: The Dish
From: "Gary Peach"
Date: Thu, 12 Apr 2001 08:42:21 +0100

Subject: The Dish

Something that I've wanted to ask, and it relates to the subject line.

"The Dish" is a movie about a NASA communications link in Australia.
I remember your file you sent me about calibrating S-Meters (something
I still consider and ruminate on, it was excellent writing). However,
that file is on another machine and my recollection insists that you
might be a participant in the story that is being told in this movie.

I did go up to Parkes before the Mission. Parkes is 50Hz and the Resdel
Receivers were 60 Hz. Thus a standards converter was necessary. The Yanks
supplied a fancy crystal controlled box of tricks about a metre cube. This
unit was distinctly unreliable and overly complex for the task which would
be more reliably done by having a 50 Hz motor connected to a generator
through a belt drive system with pulleys whose diameter were in the ratio
5/6 . This type of device could be duplicated easily so as to have a stand
by unit and the technology within the skills of the local electrician to
fix. More in a moment about what eventually happened.


You may wonder about this all. "The Dish" has just been released, so
you may be unaware of the plot line (which I cut and paste from the
net):

Synopsis: On July 20, 1969, six hundred million people sat glued to
their televisions for man's first steps on the moon. It is an image
permanently ingrained in our collective consciousness, but one that
almost didn't make it to the airwaves. Based on true-life events, The
Dish is a waggish homage to the small-town heroes responsible for a
historically almost calamitous blunder. Outside the small, sleepy town
of Parkes, a team of laid-back astro-technicians led by project
director Cliff Buxton and NASA agent Al Burnett ready the Southern
Hemisphere's largest satellite dish to transmit the historic
broadcast. But amidst a swirling media frenzy and overly effusive
civic pride, things start to go awry; the team has lost the signal and
must scramble to find the astronauts before NASA discovers their
grievous error.. And you thought Sydney 2000 was the first time we
showed the world!

I sent this on to the two guys detached from Tidbinbilla to Parkes for the
actual Mission. Both close friends. The man in charge was so upset that he
refuses to discuss the issue. I know him to be a fine Technician, and the
other guy is similarly trained. Both EX RAF Radio and RADAR trades, so not
only good technically, (they really trained us in those days), (Now they do
not train the technical people further than board jockeys and the training
facility at RAF Cosford is run as a private college and personnel may take
courses to any level including degree level. Private persons may attend the
college and many overseas persons now attend, (As did foreign military
personnel attend or training facilities back in the 50s)
The guy in charge had completed a number of years as a senior instructor
with the RAF. When I forwarded this bit of nonsense to him he was indignant
about it and said that what he'd heard of the film had made him sick and he
refused to see it.
Some how or other they had got the power monster going buy substituting
transistors of a beefier type in the power output stages. As far as they
have said it performed well.
Of course Parkes did not have a MASER so their system temperatures could not
approach those that we had at Tidbinbilla, we were therefore Prime at
Tidbinbilla and Parkes despite its much larger Dish at that time it was only
back up.
The famous moon landing was handled at Tidbinbilla because of our superior
technical performance. superior for two main reasons, 1. we had a MASER
which permitted us a system temperature of 40°K and 2. I had tuned the
waveguide distribution system to very fine standards such that we could
switch between two high power transmitter (20 kW) in less than 3 seconds. In
fact I used to do it at the touch of a button The huge waveguide switches
have to have a finite time to change over as the stored mechanical energy in
the rotors is so great that if the time taken to switch is reduced (without
my modification) the switches after a few operations would tear themselves
to pieces. If you take a butcher's at my Web page you will see a picture of
me working on my home brew Waveguide reflectometer that permitted me to tune
the wave guide over the entire bandwidth of interest (2,110 - 2,295 MHz) The
lower frequency is the up link and the higher is the downlink. Of course
diplexers and filters are used as the signal is a phase modulated carrier
therefore CW full power at all times. It is not a practical measure to work
simplex to a spacecraft that might be changing attitude quite violently and
at a distance from Earth such that even at the speed of light the signal
takes 20 Minutes to do the round trip when out at Mars distances. Even to
the moon a 3 sec delay is incurred.

Anyway enough of my digression "The Dish" is a pure fiction, and both of my
friends consider it an insult.
As I was at Tidbinbilla and apart from some sabotage three days before
launch which made the front page of Newspapers around the world we performed
to specification without a hitch.
The power supply problem was the three phase input to the power supply for
one of the klystrons. The grub screws to all three cables in the circuit
breaker bringing in the 60 Hz power that we generated on site with huge mega
watt Caterpillar generators. The cable connections arced and vaporised the
circuit breaker and the arc continued from the remaining wires and the
intense heat melted a hole about 18" diameter through the 3/16" steel
casing. Teams of our volunteer technicians worked night and day in shifts
non stop to rebuild the very complex power supply. The vaporised circuit
breaker had coated the surfaces of all components with a carbon layer. With
45 kV plus floating around at several amps that is not a good situation.
However the work was completed on time and I was able to hear Neil Armstrong
use my words, "One small step...", a few days later.

PS Sorry for the delay, I bin a bit under the weather and I wanted my
friends reactions before I made any comment, as Apart from the Power
converter week up there I really had nothing to do with the operational side
of Parkes. I did meet the famous astronomer Bart Bok. When we arrived there
was a doubtful looking character up in the dish surface dressed in shorts
and an open brown shop coat. In his hand a bucket of tar and in the other a
scrubby little brush. He was up doing some repairs. As our car pulled
alongside the Dish he came down and I taking him for a labourer asked him
where we could find the person in charge. He was a very kid and approachable
person. Later he took me on a guided tour of the structure and I was most
impressed. That was a goodish week up in Parkes and the locals were very
hospitable. I guess for much of the week I was inebriated in the evenings.
And mainly entertained in private homes of the local aristorinocracy. But
that is quite another story
--
73 de Gary7SLL
NEWBURY IO91ij
RAFARS 2757

73's
Richard Clark, KB7QHC

Joel:

Go look up a tutorial on monopulse radar. It should include the methodology for deriving tracking information from the
signal phase and amplitude at the horn(s) or other antenna at the focus. I would try to explain it, but every time I do
I get something wrong.

--
Crazy George
Remove N O and S P A M imbedded in return address
"Joel Kolstad" wrote in message ...
Hi guys,

I saw the Australian movie, "The Dish" over the holidays. It's about the
Parkes Observatory and the large dish antenna used to relay video, audio,
and telemetry feeds from Apollo 11 in 1969 back to NASA.

At one point in the movie, they lose track of where Apollo 11 is and have to
scramble to manually point the dish to get a signal again. However, once
they DO manage to get a signal, they flip a switch and the dish continues to
automatically track Apollo 11.

I'm curious... how is this down? 3 or 4 slightly offset (from the dish's
central feedpoint) receivers, the outputs of which are compared to determine
which way the transmitting source is 'drifting' (then feed back to the
motion control system to move the dish that way)? Or is there a simpler
means?

Thanks,
---Joel Kolstad

I would suspect that once the signal is found, good old well defined
celestial/orbital mechanics takes over. Even good quality optical
telescopes have a drive that keeps the instrument pointed in the right
direction.

Of course the moon travels on its own orbit buts its path would also be
well known.


Cheers Bob VK2YQA
(Who has been into the Parkes Radiotelescope numerous times)


Joel Kolstad wrote:
Hi guys,

I saw the Australian movie, "The Dish" over the holidays. It's about the
Parkes Observatory and the large dish antenna used to relay video, audio,
and telemetry feeds from Apollo 11 in 1969 back to NASA.

At one point in the movie, they lose track of where Apollo 11 is and have to
scramble to manually point the dish to get a signal again. However, once
they DO manage to get a signal, they flip a switch and the dish continues to
automatically track Apollo 11.

I'm curious... how is this down? 3 or 4 slightly offset (from the dish's
central feedpoint) receivers, the outputs of which are compared to determine
which way the transmitting source is 'drifting' (then feed back to the
motion control system to move the dish that way)? Or is there a simpler
means?

Thanks,
---Joel Kolstad

Is that the dish that's northwest of Sydney, oh, a couple hundred miles
or so? About 20 years ago I snapped a picture of a very impressive dish
from a helicopter I was riding between Sydney and Charleville (west of
Brisbane, in Qld.) Never knew what it was for, but sure looks like a
radiotelescope.

Roy Lewallen, W7EL

Bob Bob wrote:
I would suspect that once the signal is found, good old well defined
celestial/orbital mechanics takes over. Even good quality optical
telescopes have a drive that keeps the instrument pointed in the right
direction.

Of course the moon travels on its own orbit buts its path would also be
well known.


Cheers Bob VK2YQA
(Who has been into the Parkes Radiotelescope numerous times)

Hi Roy

Yep that was probably it. It is some way north out of Parkes near a
place called Alectown.

If you go to http://topoweb.lpi.nsw.gov.au/run.htm and zoom up on about
148.2639E 32.9975S, thats where the dish is. Its about 300km WNW of
Sydney so it isnt exactly in line with a trip to Charleville.

There is a smaller comms dish in a place called Moree. About 400km NNW
of Sydney. Nowhere near as big as Parkes tho. I think the only other big
dishes are south of Canberra. There is however one or two Mills Cross
arrays out there but they of course arent disk shaped!

Amd there is another dish array (6 of 22m dia) at a place called Narrabri.

http://www.parkes.atnf.csiro.au/ is the dishes actual website c/w
pictures to check out.

Cheers Bob

Roy Lewallen wrote:
Is that the dish that's northwest of Sydney, oh, a couple hundred miles
or so? About 20 years ago I snapped a picture of a very impressive dish
from a helicopter I was riding between Sydney and Charleville (west of
Brisbane, in Qld.) Never knew what it was for, but sure looks like a
radiotelescope.

Roy Lewallen, W7EL

Hah! I remember Moree. One of the folks in the helicopter (Aerospatiale
Ecureuil -- very nice machine) had a friend who lived there, and we
stopped there to refuel. After we took off, the fellow with the friend
gave the pilot regular car-driving-type directions ("go down three
blocks and turn left. . .") as we followed the road at a low altitude.
When we got to the friend's farmhouse, we circled to make sure there
were no hazards, and landed in the farmer's front yard. You should have
seen the look on his kids' faces! We went in for coffee, came back out
in a few minutes, and continued our trip. As a funny-talking Yank, I was
the novelty of the group.

Anyway, the dish I saw wasn't directly on our path, but off to one side
a bit. I'll have to dig out my notes and see if it might have been the
one at Moree. I might be able to estimate the diameter if I can find the
picture. Small world!

Roy Lewallen, W7EL

Bob Bob wrote:
Hi Roy

Yep that was probably it. It is some way north out of Parkes near a
place called Alectown.

If you go to http://topoweb.lpi.nsw.gov.au/run.htm and zoom up on about
148.2639E 32.9975S, thats where the dish is. Its about 300km WNW of
Sydney so it isnt exactly in line with a trip to Charleville.

There is a smaller comms dish in a place called Moree. About 400km NNW
of Sydney. Nowhere near as big as Parkes tho. I think the only other big
dishes are south of Canberra. There is however one or two Mills Cross
arrays out there but they of course arent disk shaped!

Amd there is another dish array (6 of 22m dia) at a place called Narrabri.

http://www.parkes.atnf.csiro.au/ is the dishes actual website c/w
pictures to check out.

Cheers Bob

Roy Lewallen wrote:

Is that the dish that's northwest of Sydney, oh, a couple hundred
miles or so? About 20 years ago I snapped a picture of a very
impressive dish from a helicopter I was riding between Sydney and
Charleville (west of Brisbane, in Qld.) Never knew what it was for,
but sure looks like a radiotelescope.

Roy Lewallen, W7EL

The Satellite industry tracks Satellites by monitoring a beacon
transmitter on the Satellite and moving the dish very slightly in a
predetermined pattern at prescribed intervals to keep the antenna
peaked. Depending on the speed of the motors and other factors, you can
track an object with an RF source as it moved fairly quickly across the
sky with this simple method.
Mike




Joel Kolstad wrote:
Hi guys,

I saw the Australian movie, "The Dish" over the holidays. It's about the
Parkes Observatory and the large dish antenna used to relay video, audio,
and telemetry feeds from Apollo 11 in 1969 back to NASA.

At one point in the movie, they lose track of where Apollo 11 is and have to
scramble to manually point the dish to get a signal again. However, once
they DO manage to get a signal, they flip a switch and the dish continues to
automatically track Apollo 11.

I'm curious... how is this down? 3 or 4 slightly offset (from the dish's
central feedpoint) receivers, the outputs of which are compared to determine
which way the transmitting source is 'drifting' (then feed back to the
motion control system to move the dish that way)? Or is there a simpler
means?

Thanks,
---Joel Kolstad