Mullard Observatory - March 2023

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This site has been covered a number of times already, but it is a cracking and quite unique place so hopefully it is of interest.

After a day spent at Duxford looking at some planes, a few of us decided to swing by here on the way home. It’s a nice easy explore and it was nice clear day, though the sun was starting to drop meaning we had to rush a bit and miss out a couple of the further dishes. The fading light made a few of the shots a bit tricky but overall it was a lovely explore.

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As this has been covered by quite a few people before, I won’t go into too much detail with the history.

The observatory was set up in 1957 as part of the University of Cambridge using a donation of £100,000 from Mullard Limited, a leading commercial manufacturer of thermionic valves (hence the name of this site.)

The site was used as an ordnance storage area previously and incorporates part of the disused Oxford-Cambridge Varsity railway line. A section of track still remains and was used to form the main part of the "5km" radio-telescope and the One-Mile Array.

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The main attraction on this site is the giant parabolic reflectors (big dish shaped things) in a long line. This is called the One-Mile Telescope (or Array) and was built in 1964 and played a key part in Martin Ryle (one of the founders of the Observatory) and Antony Hewish receiving the Nobel Prize for Physics in 1974.

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There are a number of dishes in this array. The first 2 (above) are fixed in location and as can be seen in the photo below, are climbable (albeit obviously with great care).

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Thes dishes have been stripped of a lot of the equipment and are now slowly rusting away. These are still very beautiful in a way; I especially liked the fading numbers showing the angle of the dish.

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There are other dishes mounted on rails a few hundred metres away, complete with control rooms and huts which appear to have been recently repainted. These are somewhat larger and grander looking and in slightly better condition. A couple of us were about to attempt climbing one when we noticed a CCTV camera pointing straight at it so thought discretion was the better part of valour and left it.

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The oldest telescope built on site was the 4C Array which is essentially a very long line of pylons. Built in 1958, it is 450 m long, 20 m wide, consisting of approximately 35 pylons in a perfect straight line. There used to be with a second, moveable element which has now been removed. This was the first large aperture synthesis telescope purpose made in the UK and needed 64 km (40 mi) of reflector wire which has since been removed. I am not sure when this array was decommissioned, but the last record I have seen of it being used is 1968.

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On of the later additions to the site was the Cosmic Anisotropy Telescope (CAT) in 1995. It was the first instrument to measure small-scale structure in the cosmic microwave background, which is often cited as evidence as the existence of a Big Bang. When the more sensitive Very Small Array (great name) came online in 1998, the CAT telescope was allegedly decommissioned in a ceremonial bonfire (although it looks fairly unburnt to me). The remains are essentially a massive sunken dish made up of concrete panels, as shown below.

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Certainly I know the name Mullard, vague memory Bob my uncle (by marriage) of his dad working/ have worked for Mullard say 1950's I presume management / technical. Mullard were famous for thermionic devices (ie valves) ... things which ran all our electronics, radio and tv until the transistor and latterly is often the preferred method for guitar amplification. Valves are mechanical things in a glass envelope reduced to a vacuum by means of firing a 'getter'. Theres some fascinating youtubes of Mullard valve manufacture inside their factories circa1950's. Anyway, very interesting to see this site. Interestingly, I have a copy here of Bernard Lovells 1946 book 'Electronics', aimed at the professional engineer (rescued when we cleared out Bobs dads old radio junk room in 1972) ...a treasure-trove of leading edge thermionic development and must have been a delight for its intended reader now that hostilities had ceased. Lovell had been heavily involved in radar development and at the end of the war simply pointed his mobile radar sets to the sky... leading to Jodrell Bank etc.

copyright Just-jo 2023
 
Nice write up, though you are wrong about the Varsity railway line being part of it. This 1945 aerial picture of the site shows the line being about 6/700 metres north of the site, the array appears to have been built on an east/west road that was part of the site in 1945
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