Project Cyclops, A Design... - Department of Earth and Planetary ...

1%of theantennas in the Cyclops array are inoperative.
It is very important, however, that an antenna in trouble
not contaminate the signal with a large added noise, or
with spurious signals. Further, for maintenance purposes,
any difficulty should be reported to the control
center as soon as it can be detected. Thus, a rather
elaborate self-diagnostic routine should be an integral
part
of the design.
Some of the quantities that should be monitored are:
1. Position drive servo operation
a. Position error
b. Motor temperature
c. Drive circuitry voltages and currents
2. Feed position confirmation
3. Cryogenics operation
a. Compressor and motor temperatures
b. Helium pressures
c. Receiver and maser temperatures
4. Receiver voltages and currents
5. Pump and LO frequencies and levels
6. IF level
7. Ambient temperatures (titre alarm)
8. Receiver noise temperature
9. Receiver sensitivity
10. Antenna phasing
Most of the monitoring can be done with the antenna
element in operation. It is proposed that all tests in this
category be done automatically. All that is required is a
number of transducers and a £canner that looks at the
outputs of these (or the electrical signals from various
test points) and routes the signals to a programmable
digital voltmeter or frequency counter. In addition, a
small amount of logic would be needed to program the
test instruments to their proper settings, to sequence the
tests, to compare the measurements with high-low limits,
and to initiate the proper alarm sequences when a
malfunction is detected.
As in the case of the control system antenna logic
unit, the cost of the logic circuits would be small; most
of the cost would be in the instrumentation. Both
counters and digital voltmeters have dropped substantially
in price with the advent of integrated circuits. We
believe the local monitoring function could be performed
with an equipment cost not exceeding $8000 to
$1 O,000 per antenna.
When a malfunction or abnormal reading was detected,
the local monitoring system could communicate this
to the control center in one of two ways, neither of
which requires an additional transmission system.
1. The detection of a fault could interrupt the
250-MHz 1F pilot frequency, killing the IF transmission.
A pilot sensor on the IF line could then
sound an alarm and identify the antenna in
trouble.
2. The monitoring unit could dial the computer over
the communications (telephone) system.
The relative merits of these two methods have not been
fully explored. Method 1 has the possible advantages of
instant protection against disturbing signals from the
faulty antenna and of providing a failure check on the IF
transmission system itself. Method 2 requires little if any
added equipment. In either case, the central computer
could interrogate the antenna monitoring system and
find out and print the nature of the trouble.
Monitoring functions 8, 9 and 10 cannot readily be
performed with the antenna in service. Here it is
proposed that the central computer make the rounds of
all antennas, sequentially drop them from their immediate
tasks, and make these measurements. The
measurements of noise temperature and sensitivity could
be made (with the antenna pointed at a known quiet
part of the sky) by means of a noise diode and the test
RF signal from the antenna synthesizer. The overall
phasing and gain adjustment of the array and the
calibration of its sensitivity could be made by correlating
the output of the antenna under test with that of a
reference antenna with both trained on a standard
known radio source. This procedure is discussed in
Appendix N, If a typical calibration took, say, 15 to 20
min including slewing times, all antennas would then
receive an overall monthly checkup. Together with the
local monitoring and closed-loop phase and delay regulating
systems this operation should be adequate to
ensure the health of the entire array at all times.
Naturally, all this automatic monitoring would have
to be supplemented with a regular program of protective
maintenance plus an emergency repair operation. If this
routine maintenance took one day per antenna, a crew
of 6 to 12 men could provide a 1000-element array with
regular service at 6 month intervals.
The Intercom System
It is imperative that maintenance and repair crews be
in direct contact with the control center when they are
at any antenna site. For this function a complete
telephone system with a central automatic exchange is
proposed.
The cost of the central exchange is estimated at $200
per line or roughly $250,000 for a lO00-element array
and for the office and other phones in the control
center. The cost per station is estimated at $50 or
$62,500 for the estimated 1250 telephones required.
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