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Plessey Watchman primary radar

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Plessey Watchman primary radar

Old 23rd Nov 2018, 20:37
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Plessey Watchman primary radar

I know this radar is now more or less gone from NATS units, but, I have a question. Why was the radar aerial at NATS units always mounted on enormous tall gantries (a bit like a scaffold) with proper steps ? At other Watchman-equipped units, such as Leeds Bradford, Southampton and Humberside, the aerial was/is mounted on a much more modest, slimline structure. Was the big gantry a NATS specification ? Birmingham had one, but with the distinction of no SSR aerial on top of the primary, so no extra weight to factor in.

BTW, EGNM still uses the Watchman, nearly twenty-nine years after it was installed. SSR still borrowed from Claxby.
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Old 24th Nov 2018, 05:39
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Maybe they used the original tower from a previous radar head instead of building a new one?
Farnborough's Watchman was mounted on a concrete tower (with a lift in it in which the chairman of the CAA got stuck once) which was originally built for the Plessey AR1 in the early '60s and this, being outside the airfield boundary on land owned by Qinetiq, was only demolished in 2003 when the Raytheon ASR10 in the middle of the airfield was brought into use.
The old concrete tower was built on Ball Hill, where Sam Cody lost his life.
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Old 24th Nov 2018, 11:34
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Hi chevron, I thought you might have some info !

The gantries at the NATS units (including Edinburgh, Stansted, Birmingham, Manchester and Heathrow) were all identical so it's a reasonable assumption that they were specifically designed for the Watchman. Whether that was a Plessey option or a particular NATS requirement, I don't know. Interestingly enough, the Watchman aerials at most of these units were stripy red and white. Just plain red at Leeds Bradford.

The shorter, slimmer gantries at the likes of Leeds Bradford and Southampton are identical among themselves, though with some height variation. When the LBA Watchman was installed in late 1989, it needed a completely new site as the ACR430, which it eventually completely replaced, remained in place on its concrete plinth for a few years. Perhaps a low concrete plinth wouldn't have been suitable for a Watchman anyway.
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Old 24th Nov 2018, 18:30
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Hi Mooncrest and chevvron. The Watchman at EGCC was originally on the south side, next to the Kilroe hangar. it was on a tall lattice tower just as you describe. When it was moved to the north side, just north of the 05L threshold, a similar tower was built for it. The St.Annes Watchman, which replaced the Marconi 264A, was on a similar tower too. All 3 towers had the steps leading to the top.
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Old 24th Nov 2018, 18:36
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Here's a shot I took of the St.Annes Watchman in September 2007. RYR B737 landing at EGNH in the background.
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Old 24th Nov 2018, 20:12
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Thankyou ZOOKER. That's exactly what I was thinking of. The scaffold-like structure makes me think these were designed to be easily built and/or dismantled to allow for relocation, such as at Manchester. I think I prefer them to the LBA-style structure.
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Old 25th Nov 2018, 15:42
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Must be a 'standard' design supplied by NATS when contracted to instal a radar as it looks similar to the Heathrow Watchman (which used to be on one of the fingers of T2), the Heathrow ASR10 (near T4), the Stansted Watchman and the Farnborough ASR10.

Last edited by chevvron; 25th Nov 2018 at 17:38.
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Old 25th Nov 2018, 17:27
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Originally Posted by LookingForAJob View Post
Never used the radar itself but I thought the displays were pretty good for their time.
Which displays do you mean ? There's been a few. I've seen the monochrome sets at Teesside back in '93 - I think they might have been the 'Crown' type. LBA has had one monochrome type (unknown make) and colour displays from FR, Barco and Dell since 1989. The LBA monochromes were also used with the ACR430 in its later years.
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Old 25th Nov 2018, 17:44
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The Crown displays weren't originally designed for ATC use, they were adapted from a design supplied to the RN for use with shipboard air defence radars. They worked OK in ATC though and had a built in qwerty keyboard and rolling ball and the picture consisted of 'proper' blips (albeit processed then put back in 'raw radar' form) rather than a plot extracted symbol as with TFT displays.
In the 6 years I used TFT displays at Farnborough (Nov 2002 - to Nov 2008) I never felt as 'secure' with processed radar as when looking at proper 'blips' as you were never sure what the processor had processed out that you might need to see (eg slow moving aircraft like microlights and PPGs) due to its reliance on using a 'threshold speed' of as much as 50kts as part of the processing.
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Old 25th Nov 2018, 17:45
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That sounds like the thing I used.

In fact, this looks like the beast.....

Last edited by LookingForAJob; 25th Nov 2018 at 18:00. Reason: Found a pic
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Old 25th Nov 2018, 19:49
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The Raytheon ASR10SS radar heads are supported on a lattice-tower like this one at St. Annes, 'LL, (pictured), and 'CC. Picture from Google Maps.

Last edited by ZOOKER; 26th Nov 2018 at 10:39.
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Old 26th Nov 2018, 05:55
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The consoles I saw at Teesside had the rolling ball and keyboard but different display. Probably another hybrid !

The tower in ZOOKER's last picture looks more robust and more permanent than the Watchman ones. I guess both are designed for minimum wind resistance - ideal for LBA's hilltop site.
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Old 26th Nov 2018, 15:40
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The Heathrow Watchman was never at T2 or one of its "fingers". It was beside the Perry Oaks sewage farm besides the fuel tanks now the site of T5, it almost suffered a hit from an IRA Mortar shell launched from a hotel car park northside, the shell landed after bouncing off the tarmac in front of the Watchman in the Rx site where I was working at the time, I never heard a thing.
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Old 27th Nov 2018, 00:54
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Originally Posted by P160 View Post
The Heathrow Watchman was never at T2 or one of its "fingers". It was beside the Perry Oaks sewage farm besides the fuel tanks now the site of T5, it almost suffered a hit from an IRA Mortar shell launched from a hotel car park northside, the shell landed after bouncing off the tarmac in front of the Watchman in the Rx site where I was working at the time, I never heard a thing.
Sorry you're wrong there, the radar heads near Perry Oaks were both Marconi 264s; there definitely was a Watchman midway between T2 and runway 05/23.
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Old 27th Nov 2018, 13:48
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The radar between T1/T2 and 23/05 was a Raytheon 10cm which was purchased by BAA to replace the NATS Watchman at Perry Oaks which had to be removed to construct T5. The Marconi 264's were further west alongside the settling tanks.
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Old 27th Nov 2018, 15:38
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The radar between T1/T2 and 23/05 was a Raytheon 10cm...
I'm no great expert on the Heathrow set up but wasn't that a 23cm system?
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Old 27th Nov 2018, 16:30
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The Heathrow 23cm radar was mounted on a concrete tower adjacent to Terminal 1 car park in the central landside area by the exit/entrance to the tunnel giving access to the terminals from the A4 and M4 spur. It was known as the "Car Park" radar and was removed from service and its replacement operates from Bovingdon, near Hemel Hempstead. To give better low level coverage in the absence of the 23cm radar another Raytheon ASR10 was installed southside near to T4, this supplemented the Raytheon ASR10 east of what was T2, The Queens Building and T1, these both replaced the Watchman which was sited where T5 is now. For interest the Watchman replaced the Plessey AR1 sited just north of T3 and the Cossor ACR6 which was sited south of T3 where AOSU is or was in 2010 when I retired. The building of T5 also nessesited the resiting of the DF and the Rx site.
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Old 27th Nov 2018, 18:42
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What becomes of the obsolete radar heads and towers ? NATS had plenty of Watchmans (if that's the right plural) which have all but completely disappeared. Sold on or end up in a scrap yard ?
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Old 27th Nov 2018, 19:25
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Heathrow Watchman went to Edinburgh (about fifteen years ago?). Electronics since replaced with Sensis but still driving the Watchman antenna I think
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Old 27th Nov 2018, 19:33
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The LHR Watchman went to Edinburgh if I remember correctly to replace the Marconi S511 hybrid, (Marconi Tx/Rx/Signal Processor and Plessey Aerial and Tower from the AR1. Not sure about other airport radars but probably went to the MOD to keep the military Watchman system servicable as with the demise of Plessey spares became problematic. Also as NATS had the Marconi S511 some of these went to non NATS airports as spares.
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