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Over The Horizon Radar (OTHR) and JORN

Page history last edited by Alan Hartley-Smith 12 months ago





Picture: Australian DoD




This text is an edited extract from the late Harry Cole's unpublished work "The History of the Marconi Radar Company" 1997.


The Marconi Company had carried out work on Over-The-Horizon radar successfully in 1952: using a wavelength of 13m and a 100µs pulse from a 1kW transmitter, aircraft echoes were readily seen in the presence of competing sea clutter by using filters of an effective bandwidth of 1/3 Hz using a 3s integrating time.


The antenna array directed its beam out to sea off the Cornish coast. The development of microelectronics and microprocessors made the engineering of a modernized version of OTH a viable proposition. Work on a new OTH had begun in the late 70s and was stepped up in 1982. A prototype and development model was erected to operate across the Dengie Marshes and out to the North Sea.


The site was about 3km from the shore and about 8km north of Burnham-on-Crouch. Using phased array techniques, the antenna generated a set of 'receive-only' beams covering 90°. A wider transmitting beam was sequentially stepped through this quadrant executing its scan in two minutes. The dwell time of several seconds at each step allowed the receiving beams' contents to be analysed by a 4096 point FFT filter battery. Such fine discretion in the Doppler domain was made possible by the great speed of today's microprocessors.


Editors note - new insert from "Britain's Cold War By Bob Clarke"
The Royal Radar Establishment (RRE) developed an experimental radar, code name Orange Poodle, in 1952-53, primarily to explore Over-The-Horizon Radar (OTHR) theories for the Government. The trials were aimed at detecting moving objects, aircraft or ships, below the radar horizon (beyond the curvature of the earth), using the ground-wave effect.

Marconi became lead contractor on the project and developed the transmitting equipment, slinging a broadside array between two timber towers at the Chain Home site, RAF Downdeny, on the Cornish coast.

Small-scale trials in 1953 demonstrated that the concept had potential, designated aircraft were tracked and the equipment was able to discriminate between sea waves and the target. Unfortunately the system, when tested against basic jamming equipment, showed that it would be very easy to disrupt a network of sites if they were commissioned. Subsequently Orange Poodle was scrapped, but the concept and requirement for OTHR continued.



In the early 1990s, under the stewardship of Ken Perry, Business Development Manager of the day and a stout pro­ponent of OTHR, the Company was successful in winning a large contract to design and supply an OTH system to Australia.


The project was to furnish a radar network across the entire length of the North coast of the country - all 2400 miles (3840km) of it. In the face of fierce competition, the Company won the contract in June 1991.


Teamed with Telecom Australia, a new Division was set up in Melbourne — GEC-Marconi HF Systems — to run the JORN project (Jindalee Over­ the-Horizon Radar Network) as it was called. Multiple 20kW solid state amplifiers working into an antenna array 300 yards (275m) wide gave the 500kW transmitter power required. 90 miles (144km) away, about 500 antenna masts in a straight line stretching for two miles (3.2km) formed the receiver station. The 500 elements were grouped in sub-arrays of twenty-five. The twenty sub-arrays served processors in bunkers whose digital outputs were passed on fibre-optic links to the receiving centre where position data on targets was extracted. Six hundred miles away, the Radar Operations centre carried out further pro­cessing to derive tracks and target categorization for feeding to Air Defence Centres and other users. The JORN system covered 3% of the Earth's surface, processing the results of surveillance once every minute, 24 hours a day.

Such a large offshore project could not be run from the UK and about 200 staff were transferred from Chelmsford to Australia.

To me, the JORN project is highly significant in historical terms. It typifies our Founder's tradition of doing very big things with the latest technology. It has the grand sweep of a breathtaking idea, successfully carried to fruition. I'm sure he would have been delighted to see his two inspirations — wireless communications and the idea of radar — wedded together.






JORN Prequel


From David Emery

I did not work on JORN, though have inherited various papers from Mike Lewis, Ken Perry and John Bodonyi (amongst others). A JORN timeline, which I suspect may have been written by Ken includes the following succinct entries:

1985 - presentations to RAAF in Canberra by MRS (Air Cdre Sismore and Ken Perry) on sky wave and surface wave design/build capability.

1989 - DoD issues competitive RFP for JORN. Marconi Radar responds with Ken Perry 70 page proposal, hand-written and faxed to Sydney late Friday evening when MRS all gone home and phone lines clear.

1990 - John Bodonyi writes advanced, detailed technical proposal, alone in Melbourne hotel room. MRS team of 6 join him to expand this and present to DoD / RAAF in Canberra. Dr Brent Summers MRS designs advanced signal processing system.

1991 - TA / MRS awarded JORN contract, beating Raytheon and General Electric.




Australian Telecom 1993 JORN Newsletter "Over The Horizon"


Early Telstra Brochure: "This is Jindalee"


A technical brochure 1. 2.


Article from Jane's Defence Weekly "Australia's Jindalee Radar finally poised for operations"


Marconi Organisation Charts and Personnel in UK and Australia during the period 1995 - 1997


JORN Audit report


by Engineers Australia, Engineering Heritage Victoria
(A nomination under the Engineering Heritage Australia Heritage Recognition Program)
Dated 2016, this document is a well-written, readable, comprehensive and laudatory description of Jindalee, JORN and their history, replete with useful references. Ken Perry's contribution is detailed and Ted Pegram, Gerry Valentine, John Bodonyi, John Pearce and John Sutherland all get mentions as do BAE Systems and Marconi Radar.

(Editors note - the URL reference in this document to Jindalee Weather is now <http://jindaleeweather.com/>)


Wikipedia entry 


Australian Government DoD paper


Construction of Jindalee site


Comment from Malcolm Mack

JORN was probably the most interesting engineering project that I ever worked on. I learnt a considerable amount about subjects that I never dreamed of experiencing in a European environment. Some of these which won’t set the world on fire, are as follows :-

Termites:- Did you know that the Australian Standard lists over 300 members of the species. Their habitats and bad habits.

Noise:- The parameters of adiabatic noise on circuitry in the context of power generation.

Dust:- Did you know that there are Qty 4 test dusts for calibrating filters.

Flora:- There is a vine in Western Australia whose roots seek out underground cables and strangles them to death.

Fauna:- Parakeets, Lorikeets, Cockatoos – Depending upon which part of the continent, some attack overhead cables. Telstra had a test bed for cables in the bird cages up at Healesville Sanctuary.

Wombats:- Nature's bulldozers, that undermine buildings.

This all before we get to spiders, snakes and crocodiles…


"Mulching Matilda" - a personal view of working in Australia by Ian Gillis.




Input from Steve Bousfield:





The following is a simplified explanation of the OVERSEER over-the-horizon radar. It reflects my, possibly flawed / mis-remembered, understanding from several years ago. My apologies to those who have a superior knowledge of the system. Please provide corrections as necessary.



Overseer is a bi-static HF Surface Wave Over the Horizon Radar designed for the surveillance of the Economic Exclusion Zone including such things as anti-drug and anti-smuggling operations. It can replace the need for expensive maritime or airborne patrols and facilitate targeted interception.


Effective against both surface and airborne targets, a single installation can monitor a 120 degree sector with a range on small surface craft of 65km and up to 200nm on larger targets. Actual performance varies with local conditions including the salinity of the sea.


The system comprises an antenna array with a number of antennas that varies according to the operating conditions in the area, transmitters and receivers and local and / or remote operations room.


The antennas are installed along the shoreline with their ‘feet’ wet. The transmitted signal propagates itself not only into the atmosphere but also along the sea’s surface thus achieving the over-the-horizon capability. The transmitted signal resonates with vertical metal surfaces in its path and it is this resonation that is detected and processed into targets for display to the operator. This takes considerable processing power and it is only the advances in this technology that have made the system practical and cost effective.


This type of detection is quite different from that offered by conventional radar which relies upon reflections from metallic surfaces.


Because the system uses resonance from vertical edges rather than reflection it is effective against small wooden or RIB type craft that usually have either a long radio antenna or metal mast, even the mounts for an outboard motor will provide a suitable ‘target.’ With aircraft it is parts of the structure like the vertical tail plane that give rise to the resonance.


These two animations show a typical installation, a representation of how the system works, with additional captions.




A demonstration system installed at Dengie was capable of monitoring movements at the port of Rotterdam as well as traffic at Amsterdam’s Schiphol airport.


HFSWR Demonstration Site at Dengie, Essex
Alan Batchelor at Operator's Display

JORN Subsystem Prototype team at the Dengie HF Radar.

L/R: Alan Batchelor, Jim Waddell, Nick Richards, Dave Walters and Nigel Thackray in Sept 1995.




This is the current BAE system.


Input from Bernard de Neumann

The antennas shown were, I believe, invented by Alan GP Boswell of Marconi Research in the early 1990s. The tetrahedron elements are easily packed compactly for transportation, and easily unpacked, so they may be deployed quickly in difficult terrain.


This paper is a detailed technical exposition of OTHR [Editors note - large file]


JORN Phase 6


(Extract from the Australian Defence Business Review June 2019)


"This project – AIR 2025 Phase 6 – is not without risk and is a very significant undertaking. The underlying technology and software are uniquely Australian, and we are in it on our own – there is no foreign partner to carry most of the risk.

However, the JORN Priority Industry Capability (PIC) Support Program performed by BAE Systems and Lockheed Martin in conjunction the Defence Science and Technology group (DST) and Defence Capability Acquisition and Sustainment Group (CASG) significantly reduced this technical risk prior to contract award.

The 2016 Defence Integrated Investment Plan (IIP) cites a project cost of $1-2 billion over the period 2017-26, and describes Phase 6 thus:

“The Jindalee operational radar network will be enhanced through a spiral development program into the 2030s in order to realise its full potential as a wide area surveillance capability.

“Enhanced command, control, communications, computers and intelligence integration will allow Jindalee to cue and be cued by other systems across the sensor network.

“The core role of these systems is the defence of Australia and its surrounding airspace by identifying aircraft and some surface vessels approaching Australia.”

See links http://adbr.com.au/over-the-horizon or http://baes.co/ss7W50xUH5b


Over-the-Horizon Radar at RAF Feltwell

This is an article written by David Emery (with an editorial comment) - acknowledgement to the Feltwell Parish Magazine, issues September/October 2020


Over-the-Horizon Radar at RAF Feltwell
By D. J. Emery

"Editor: Regular readers may recall that a few months ago I published a request by D. J. Emory relating to an early warning system that had been installed at RAF Feltwell during the Cold War. Mr Chris Cock was able to provide some information which was later confirmed by others. Here is a shortened version of David’s much more technical article, that he has written specifically for us."

One problem which preoccupied America throughout the Cold War was that of providing early warning of any attack from the Soviet Union. One such system involved in attempting to provide this early warning was the 440-L forward-scatter over-the-horizon radar, a component of which was located at RAF Feltwell.

The concept for the system had been developed in the USA, where a research programme was undertaken at Stanford University in 1962- 63, and similar work was performed by the Air Force Cambridge Research Laboratories (AFCRL) under project CAME BRIDGE. The early experiments were sufficiently successful that in 1965 a formal programme office was set up by the United States Air Force, with an original target date of August 1968 for a fully operational system. There were a number of delays and changes at the start of the programme, but eventually four transmit sites in the Far East were used, along with five receive sites in Europe. The transmitters sent out a continuous signal in the HF band (5 - 25MHz) which, via ionospheric refraction, would reach the receivers over-the-horizon in Europe. Any perturbation of the signal could be interpreted as a missile launch along the radio propagation path, thus triggering early warning of attack.

The transmit sites used were:


T-1: Wallace Air Station, Philippines
T-2: Awase, Okinawa
T-3: Tokorozawa, Japan (HQ in the Far East) T-4: Chitose, Japan

The receive sites used were:
R-1: Cyprus
R-2: San Vito, Italy
R-3: Aviano, Italy (data correlation centre) R-4: Rothwesten, Germany
R-5: Feltwell, England


The site at RAF Feltwell formally began operation (with an “Initial Operating Capability”) on 1st March 1968, being manned by 15 Comm. Sq. OL A1 Unit of the US Aerospace Defence Command. The equipment consisted of highly sensitive receivers (FSQ-76) connected to a large array of tall antennas. Despite official views to the contrary (Historic England state that all that is left of 440-L at Feltwell is a prefabricated hut) it can be seen that there are still some physical remains of an HF antenna array which was probably used in the 440-L system. A short distance to the north-west of the Precision Measurement Equipment Laboratory (PMEL).


Just to the north-east of the PMEL building, there are eight large square concrete blocks which probably formed the bases for the antennas [See image below]. They are approximately 11m apart and are aligned such that the main beam would be pointing on a bearing of 42deg, precisely the right direction to receive a signal from the Far East. There are hints of a larger array (with the antenna elements spaced at 30m apart) further to the north-west which may also have been used, and a third array of 9 elements stood to the east of the PMEL building (now under the golf course).

The 440-L system was closed down in 1975, after concerns had been raised about its reliability, and also press reports describing its interfering effect on Japanese television (New Scientist, March 1975). The increasing importance of satellite technology may also have contributed to its closure.

Associated with early warning of attack itself is gaining intelligence on enemy weapon development – such as missile and nuclear testing. Earlier in the 1960s, Feltwell was involved in Project Clear Sky – a joint US/UK programme to monitor the nuclear test ban treaty. As declassified documents now show, a number of techniques were used at RAF Feltwell for this monitoring, including sensors using acoustic, geomagnetic, fluorescence and VLF Phase techniques. Furthermore, a declassified document in the National Archives suggests that RAF Feltwell may also have been involved in a British Over-the-Horizon radar known as Zinnia.

If any readers have additional information about 440-L or any of the other systems mentioned, the author would be most interested to hear from them via the editor.

Google Earth image of the eight concrete antenna bases at RAF Feltwell probably used in 440-L



Over-the-Horizon Radar at RAF Feltwell
"Last month, you may recall, we published an article by David Emory about an experimental early warning system that was partly based at Feltwell. This article generated the following email from Mr Chris Cock.

“Had a chat with Mr Stiff who lives by St Nicholas yesterday. He told me that he built the shed which was alongside those Aerials on RAF Feltwell. He didn't know what it was for but was told at the time it was to be used for "Upper Met Research."

On the same day that I received this email I was doing one of my 5-mile walks for Prostate Cancer when I bumped into Mr Jeremy Porter. We discussed the article and Jeremy told me about a speaker system that his father, Edwin Porter, had had on his desk when he was the Chair of the Parish Council. Apparently, the device had to be listened to at a certain time and at regular intervals. Generally nothing came out of it but static but occasionally there was a message. Jeremy wondered if it had anything to do with the early warning system.

So, I messaged David about these two incidents and this is his reply:"
“Upper meteorological research” seems to have been a cover name (not entirely inaccurate) used by AWRE and other agencies for radio methods (and perhaps others) to detect nuclear explosions / missile launches. It seems to have been used at Orfordness too, where there was another over the horizon radar (before the more famous COBRA MIST system).

I’m not an expert on the warning infrastructure but the Parish Council device may possibly have been a “carrier receiver unit” whose purpose was indeed to receive warning of an imminent attack. There were some 19,000 of them installed in rural locations and they were at the end of a one-way line.


Photo of device



"Next time I see Jeremy I’ll have to ask him if this is the device he remembers seeing. As a former Parish Chairman myself I can’t imagine the responsibility of having one of these and what it must have felt like to listen to the message. Edwin must have worried each time he pressed the button and been very relieved when he didn’t get any bad news. Thankfully."


Link to article


Ocean Surface Current Radars








Comments (5)

Ian Gillis said

at 12:41 pm on Feb 17, 2016

Page checked

David Emery said

at 3:52 pm on Feb 26, 2016

I believe the early OTHR system Harry is referring to was code-named Orange Poodle. The trials were undertaken at RAF Downderry in 1953, with an array being constructred between two timber towers. Although successful to a certain extent, the system was thought too susceptible to jamming. ['Cold War - Building for Nuclear Confrontation 1946 - 1989', Cocroft and Thomas]

Alan Hartley-Smith said

at 4:48 pm on Feb 26, 2016

See new insert.

David Emery said

at 7:45 pm on Feb 26, 2016

David Emery said

at 7:47 pm on Feb 26, 2016

You will need to be a subscriber to the IEEE library in order to access the papers.

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