Jodrell Bank

The Very Small Array

A major project undertaken by the Receiver Group at JBO has been to design and build the 30 Ghz receivers required for the Very Small Array, which is installed at the Observatory on Mount Teide, Tenerife. Observations at such high frequencies are not practical in the UK due to the amount of water vapour present near ground level in our atmosphere; hence the site on Tenerife at a height of 2.5 km is far better.

The receivers, with their horn antennas will form an aperture synthesis array to give the resolution of a much larger system - defined by the size of the array - but capable of simultaneously observing a much larger area of the sky than a single large antenna.

The VSA is being used to make exceedingly sensitive measurements of the Cosmic Microwave Background to learn about the early Universe.


The site of the Experiment enclosure and control building seen from the south east

Array top view west side

Current configuration of Array
viewed from above the table and from the west side of the table

VSA Cryostat image

Receiver mounted in it's support cradle

30 Ghz Low Noise Amplifier

30 Ghz Low Noise Amplifier

The broad-band 30 Ghz low noise amplifers have noise temperature around 15K and are based on a design originated by Marian Pospieszalski at the National Radio Astronomy Observatory (NRAO) in the USA.

30 Ghz Receiver System

30 Ghz Receiver System

The receiver and part of the feed horn is mounted within a cryostat cooled to approximatly 15K by the use of a compressed helium refrigeration system.   The system noise temperature of the VSA Receivers is of order 30K which is a factor of two better than the earlier generation receivers currently in use on Tenerife.

Refrigeration equipment

Refrigeration equipment used to cool all receivers

Current Status

Since October 2000 the telescope has been performing regular observations of the three initial VSA fields using all 14 receivers in the main array and both source subtraction antennas. Analysis of the data is being performed separately by Jodrell Bank Observatory, Institute de Astrofísica and Cavendish Laboratories. The final two receivers were delivered in December 2000 and replaced existing under-performing receivers in the main array. The opportunity was taken to change the array to a compact configuration at this time, to produce the required sensitivity level in a more reasonable, shorter, observing time. Some outstanding construction work was also completed and the system made ready to survive the ravages of a mountain winter at a height of 2400m. During late February and early March the two spare receivers were improved and returned to the island. These took part in the large horn tests held during the Summer. September saw a massive technical effort on Tenerife to convert the compact array with small horns to an extended array with the recently constructed larger horns. This involved the removal of every receiver from the main table, separation of horn from receiver and the fitting of new larger horns. Since all receivers would at some point be available for maintenance during this process, we took the opportunity to cryogenically service as many as possible. Much preparation was required to create an indoor laboratory suitable for a technician to dismantle such delicate instruments in a relatively clean and dust free environment. All specialized service tools and spares were shipped well ahead of time to ensure arrival on site before technical effort arrived. Several JBO technicians were involved at various stages, overlapping with each other to achieve the desired spread of knowledge and capability whilst leaving some effort to keep MERLIN running. The New York twin towers disaster occurred part way through these visits and did much to disrupt air travel for the unlucky few. Delays were inevitable, along with lost and damaged baggage. Despite this spirits remained high and the job was completed in time to allow the receivers to be re-mounted and cooled whilst we were still on site to supervise. In spite of needing to turn off all receivers and cooling plant to carry our this maintenance, all returned to normal after the service, a compliment to good design and our continued hard work. Some receivers remain to be serviced but, generally these are the later units and have only operated for a small number of hours. These will be examined during our routine visits over the next year.

February 2002 As part of our routine maintenance schedule, two JBO staff attended site during Feb2002. A variety of tasks were undertaken to maintain the high level of reliability already achieved with the experiment.


Work adjacent to the source subtraction enclosure on the spare Edwards E2M28 Vacuum pump.


White APD helium compressors being inspected for coolant leaks after adsorber servicing


Cable and coolant tube tidying after final compressor inspection.


The source subtraction helium compressor being examined to locate a small oil leak.

Source sub

Cabling to source subtraction receiver being secured

Large bore

A large bore flexible hose being fitted to the system main array.

Air blast

Operation of air blast fans being evaluated within cooling compound.


Chiller housing being replaced after operational check.

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