In late 1964, the Jupiter Monitor was installed at Carnarvon as part of a world-wide network.

In addition to Carnarvon, the Jupiter Monitors were placed at Kano, Nigeria; Hawaii; and the Goddard Space Flight Center in Maryland.

At Carnarvon, the Jupiter Monitor was part of the SPAN (Solar Particle Alert Network) installation.

 

The two Jupiter Monitor masts are labelled in red on thsi February 1966 aerial photo of Carnarvon, looking roughly south.

 

This article from the MSFN’s Technical Information Bulletin, Volume 2, No. 21, was published in October 1964 and provides some helpful background –

Jupiter Monitoring Network to be Implemented
TIB Vol 2 No. 21, October 16 1964

During the latter part of the current year, radio monitoring sites will be implemented at three MSFN stations – KNO, CRO, and HAW – and GSFC to form a worldwide radio monitoring network to aid in the study of the planet Jupiter.

As its primary function, this network will maintain a 24-hour radio monitor of low-frequency radio noises sporadically emitted from Jupiter. First noticed in 1955, these signals have been observed throughout the frequency range of from 10 to 50 megacycles.

Statistical data will be collected on two frequencies –16.5 and 22.2 mega­cycles – and will shed light on the mechanism of these low-frequency sig­nals. This information will be used to reap further data about the planet’s magnetosphere. It also will reveal valuable research information about the properties of the interplanetary medium and the earth’s ionosphere.

The four radio monitoring sites com­ prising the worldwide network will be located approximately 90 degrees (longitude) apart around the world so that Jupiter will always be in sight of at least one of the sites.

Since only one of the four radio mon­itoring sites will be able to observe Jupiter during any given time period, the three remaining sites will be free for other astronomy studies. As a secondary function, the sites will monitor the sun to provide additional radio noise data. This will be correlated with the Jupiter data to see how solar activity affects the Jupiter radio emissions.

The monitoring sites will consist of a receiver, a strip chart recorder, an automatic antenna programmer, and two Yagi antennas mounted on 40-foot poles. The automatic antenna programming system, driven by sidereal and solar clocks, causes the antennas to track Jupiter when Jupiter’s local hour angle is between 4-hours east and 4-hours west. If Jupiter is outside these limits, the antennas are automatically slewed to the position of the sun and track the sun between the limits of 4-hours east and 4-hours west. If neither object is within the local hour angle limits, the antennas set themselves directly overhead at the meridian. In this position, relative ion­ospheric opacity measurements will be made which will provide information on the absorption of the cosmic radio signals by the earth’s atmosphere. This data will be correlated with the Jupiter and sun radio emission data.

Although a number of observatories have been studying Jupiter’s low-frequency radio emissions since their discovery, none has been able to make uninterrupted observations. These observatories are generally located along the east coast of the United States and can monitor Jupiter only during the daily 8-hour period when the planet is in good radio view from this coast.

The monitoring sites are planned to be operational by early next year. Those sites to be implemented at MSFN stations will be installed and maintained by MSFN M&O personnel.

 

The Eastern antenna of the Jupiter Monitoring Array in May 1966. Photo preserved by Trevor Mosel. Scan by Stuart Wattison.

And from Paul Dench’s website, carnarvonspace.com –

Each of the two antennas had a Yagi array on each end of a 25m boom receiving signals at 16MHz and 22MHz. While Jupiter was not in view the two-antenna interferometer turned towards the Sun to add detail to the SPAN data.

During the Jupiter Monitor installation there were a couple of orientation problems. First Carnarvon had received an incorrect set of eight quadrant plates to connect the array booms and antenna drives to the masts; they were supposedly machined to present the antenna at the correct declination angle relative to Carnarvon’s latitude. Apparently the plates had been randomly selected from the 136 plates to be distributed to the seventeen Jupiter Monitor sites around the world. Rather than wait for the delivery mess to be sorted out, Carnarvon redrilled the plates to suit the local latitude.

The second problem was the antenna drive box. It consisted of a series of cascaded worm-gears driven by a large reversible double-ended motor to fast slew the antenna in either direction. Once it had reached the required tracking position, an electromagnetic clutch then switched to a small unidirectional synchronous tracking motor.

Jim Gregg recalls the ‘mechanical program’ as “…an electromechanical marvel of Perspex disks with hour angles marked on them driven by the other ends of the Selsyn links, [with] … lots of micro switches … [and looking] like something made by an outback lawn mower repair shop.” The ‘computer’ was switched on and seemed to do all the right things; indicating Meridian and tracking at the right rate, “So we told it that Jupiter was just rising … [and] watched in total disbelief … [as the antennas] slewed down to the Western horizon, stopped, and started to track towards the East” – the opposite to what was required. Obviously the 'mechanical program' had been set for northern latitudes where a station would look South and track from left (East) to right (West). For southern latitudes the antennas needed to be turned by 180° to look North, and track from right (East) to left (West).

Before NASA had responded to the problem the local team had worked out a solution. The small tracking motor was completely symmetrical, so its stator was removed, turned end-to-end, and reinstalled to run ‘backwards’. CRO then swapped ‘direction’ connections on the slew motors and Selsyn data lines and everything worked perfectly. A ‘Change Recommendation Request’ (CRR) was sent to NASA; this was accepted and dispatched to the other seven southern sites.

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