Visiting "The Dish"
On December 12, 2004, Darryl Smith, VK2TDS, and I were lucky enough to
CSIRO 64M Radio Telescope
near Parkes, NSW, Australia. In addition to being an important site for
radio astronomy, this is where the TV signals from the first moon landing
in 1969 were received. A reasonably fictional, but very enjoyable,
movie about Parkes' role in the Apollo 11 mission is
Andrew Hunt, a CSIRO staffer, was kind enough to give us a full tour of
the facility. I've been to a few other sites that house big dishes
(including the BT earth station at Goonhilly Downs in the UK, and the NASA
Deep Space Network station at Tidbinbilla near Canberra, Australia) but I've
never had an in-depth tour like this one. Thanks, Andrew!!!
Here are some pictures of our visit.
John in the Maser Hut
The hydrogen masers used to control the frequency of the receivers and
provide precise timing information for interferometry are located in a
small temperature controlled hut. There are two masers -- one a
"Smithsonian" unit, and the other a newer Russian unit. An HP 5065A Rubidium
standard is also in the hut, but these days it mainly serves as an
expensive thermometer -- its phase record shows whether there's a
problem with the temperature control!
Andrew and the Computer Room
The observatory now has over 100 computers on site. Taming the RFI is a
real challenge, and if you look at the side of the rack, you can see
screening that's part of the attempt at RFI control. The left side of the
first rack contains several custom correlator cards. These are high speed
digital signal processing units, designed by Andrew and the CSIRO team, used
to time-shift and combine the signal from multiple receivers for
Part of the Receiver System
This rack contains mixers and signal routing equipment. The patch cables
make me feel that my own shack isn't so bad, after all. The local
oscillators for the receivers are generated by HP signal generators locked
to the maser -- unfortunately I didn't get a picture of the rack of
GPS Frequency Monitoring
Darryl and I noticed a monitor with a familiar screen -- it's the original
DOS version of Tom Clark's "Showtime" software used with the
GPS timekeeping interface. Since both Darryl and I are on
TAPR's Board, and I have a couple of TACs (including one of the beta units)
in my basement, it warmed our hearts to see TAPR's stuff at work here.
CSIRO uses the GPS system to monitor the frequency offset of their masers.
If my count was correct, they had at least one TAC, as well as a couple of
which are a commercial version of the TAC. In addition to using the GPS
1pps signal, they do common-view GPS comparisons with another site in the
Australia Telescope network. They currently keep the two sites synchronized
to within about 4ns.
Lots of Data
Darryl and Andrew on the Catwalk
The Interferometer Dish on the East/West Track
(From the Catwalk)
The Original Access Road
As Shown in "The Dish"
The "Rotor Loop"
At least, that's what we hams would call it. This is the central support
of the dish, showing the flexible feedlines dressed to allow 360 degree
Andrew's specialty is maintaining the electronics that control the precise
movement of the dish. This cabinet contains the motor controllers.
Equatorial Aiming Scope
This is one of the neatest features in the dish's design. This device is
mounted at the center of the dish mount. Due to its small size and shielding
from the elements, it can be aimed very precisely. Once it is aimed, the
big dish is moved to about the right location, and then a laser and
photodetector system automatically adjusts the dish to keep it pointed at
exactly the same spot as the aiming scope. Any error due to wind or
mechanical slippage is automatically corrected.
The Last Chart Recorder
This is the only chart recorder still running at Parkes. It's used as
part of the VLBI system. I checked the chart, but didn't see any wiggles
This is the front end (cryogenic amplifier and downconverter) for the
receiver used to monitor several of the NASA Mars missions currently