Plessey Watchman primary radar

[Mooncrest]

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.

[chevvron]

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.

[Mooncrest]

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.

[ZOOKER]

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.

[ZOOKER]

Here's a shot I took of the St.Annes Watchman in September 2007. RYR B737 landing at EGNH in the background.https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/612x930/screen_shot_2018_11_24_at_19_35_59_94df6de544dd5544f61acf408 f3dd5745963c237.png

[Mooncrest]

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.

[chevvron]

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.

[Mooncrest]

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.

[chevvron]

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.

[LookingForAJob]

That sounds like the thing I used.

In fact, this looks like the beast.....
https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/305x350/p118_eadebc2b446f99940e09a83825f1ad5ac38107eb.jpg

[ZOOKER]

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.https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/1292x748/ll_asr_1e3f329adff8f9cce5a1bb1e0a0fb9ae49321c32.png

[Mooncrest]

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.

[P160]

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.

[chevvron]

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.

[P160]

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.

[LookingForAJob]

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?

[P160]

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.

[Mooncrest]

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 ?

[NorthSouth]

Heathrow Watchman went to Edinburgh (about fifteen years ago?). Electronics since replaced with Sensis but still driving the Watchman antenna I think

[P160]

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.

[chevvron]

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.
Apologies; I remember the Perry Oaks Watchman now. Vague recollection that a Heathrow controller told me they didn't use it much as its site meant it had poor low cover, plus it was in the way of T5 development.
When Farnborough opened LARS East, the T2 10cm was piped in but we preferred to use the Pease 23cm or the Car Park 23cm until one day a NATS engineer came down, fiddled with one of our displays, then got up and left after announcing we now had the T4 10cm instead of the T2 one. Course we couldn't use it straight away as he didn't leave us any paperwork but next day I was on LARS East and had it selected when a helicopter called me between Herne Bay and Reculver at 800ft and to my amazement I could identify it! I found the low cover from this radar was superior to the Car Park 23 cm so from then on, used it in preference.

[chevvron]

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 ?
The Farnborough Watchman was owned by MOD so they took that back and installed it elsewhere (mid 2003), but they didn't want the consoles as these were being replaced by raster scan displays so they were left in situ when the old tower was demolished in 2003. We did have a 6th console in the final few months of the old tower and this was a raster scan one so we all assumed this is what we would get in the new tower but we got TFT displays instead although the CAA were reluctant to approve them until very close to 'O' date (22 Nov 2002); can't remember what happened to that console or whether it was owned by NATS or MOD.

[Mooncrest]

Nice to see there is life in the old systems after their heyday, as it were. Otherwise, there is a lot of scrap metal in the gantries, towers and aerials (assuming they're not made of fibreglass).

[chevvron]

Nice to see there is life in the old systems after their heyday, as it were. Otherwise, there is a lot of scrap metal in the gantries, towers and aerials (assuming they're not made of fibreglass).
Now you come to mention it, I think the Watchman reflector was fibreglass.

[P160]

You are correct Chevron, it was a composite sandwich. Outside layers of glass cloth and epoxy resin with an inner metal sheet layer of aluminium, after all, glass cloth and resin are transparent to radio waves.

[LookingForAJob]

Thanks for the info P160 - didn't realise there were so many heads around Heathrow.

[P160]

Just for interest, when I first started at LHR in 1978 there were four Marconi 264H radars, one Cossor ACR6, one Plessey AR1 and one Decca ASMI surface movement radat. When I left in 2010 there were two Raytheon ASR10's and four Terma SMR's plus two Qinetic FOD radars, and they all worked magnificiently despite my efforts and harsh language.

[Mooncrest]

I suppose you can never have too many radar heads, provided they compliment, rather than cause grief with, each other. Glasgow once had a pair of Marconi 264s and Leeds Bradford kept the ACR430 going for several years after the Watchman was commissioned. It will be interesting to see if LBA plumps for its own SSR aerial when the Watchman is replaced, which can't be too long away.

A thought has just occurred to me. Are radar towers meant to be frangible or not ? It might depend on proximity to runways, protected bits and so on.

[P160]

Radar towers to the best of my knowledge have never been constructed with mechanical fuse pins to make them frangible due to the tremendous side loads imposed on the structure during high winds and also because they are usually well offset from the direction of travel so to speak. The only frangible airfield installation I came across was the STAN 37 Localiser which had aluminium fuse pins between the ground mounting bolts and the lattice uprights.

[Mooncrest]

Thankyou P160. I never considered those points, plus the weight of the aerial would call for a robust structure. Glidepath aerials, on the other hand, are definitely designed to give. I've seen the sorry remains of one at LBA.

[ZOOKER]

This is a picture I found via Google Images, taken by George Woods, and shows the Marconi 264 that was mounted on the Maintenance Area MSCP.. I believe it was sited to give LATCC improved low-level coverage, possibly before the EGCC HSA 23cm tower was built?

Rumour has it it's short lifespan was due to it's effect on TV/radio reception close to the site? I know the EGCC 264H had the same feature, a short 'buzz' each time the aerial rotated. It even affected the cassette-recorder I had as part of our 'directed studies package', provided by John Dougan

The Sub-Centre ops room was screened with mesh and industrial-grade tin foil, as the beam's passage also affected the Mediator System Displays.https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/1194x746/screen_shot_2018_03_30_at_11_50_43_83a7b9440c6c5ca5326817c80 9a243cc96fda885.png

[Mooncrest]

Fascinating picture ZOOKER. I hate to be contrary but is this definitely EGCC - Manchester ? I remember the 264 but it was mounted at ground level near the RW24 threshold, as I recall. Also, I don't remember a spiral ramp at the multi storey car park. Nice Egyptair 707 as well.

[P160]

That image is the LHR Marconi 264 atop of the BA staff car park in the BA maintenance area east of the terminals and yes, that with the other three 264's did cause TV interferance which is why we no longer use the 50cm band. The body responsible for frequency allocation, the ICU decreed in the mid 70's, the closure of the 50cm to civil radars. The TV band overlapped the 50cm band hence the interferance so all users of this band were made to discontinue usage, the 23cm and 10cm are the lowest bands available for civil radar. This happened in the late 70's into the 80's to allow withdrawal and installations of radars, the LHR 23cm became operational about 1984/85. The BA car park radar was replaced by the EN4000, a hybrid of AR1 Tx/Rx, Marconi 7113 processor and a Cossor ACR6 aerial.

[Mooncrest]

Thankyou P160. I didn't think I was looking at Manchester but I couldn't have been certain it was Heathrow either.

[HEATHROW DIRECTOR]

The best radar we had at Heathrow was the ACRVI, especially when one of the Tels chap ("Tiny") got his trimming tool in it and tweaked it up!

[ZOOKER]

Mooncrest, yes apologies it is a slightly ambiguous post. The picture is, as P160 says, the BA base on the east side of EGLL. The 'CC 264 was originally sited NW of the R/W 20 threshold, about where the cargo sheds are now. By 1979, it had moved to where you say, roughly where the MCT DVOR is sited today. There was a rumour that the EGLL 264 aerial from the BA car-park was used to replace the one at Manch', but I don't know whether that is true.

[chevvron]

I thought the short lived radar on the BA car park was a 23cm Marconi 654, replaced by the 23cm HSA radar on T1a car park.
We had a 50cm Marconi 232 at Farnborugh until the Watchman was installed, 1991 I think and it too made a 'beep' on the RTF every time it rotated.
I believe there was a 10 cm Plessey AR15 at Luton which wouldn't interface with other LATCC radars so it was just switched off and left there.

[Mooncrest]

This radar business is clearly far from simple. Different towers and plinths for mounting, numerous possible sites, different manufacturers, assorted wavelengths, displays and individual nuances. An interesting subject.

I wonder if Talkdownman at Lasham would like a Watchman or S511 when the 424 eventually pegs it ?

[P160]

Chevton, the BA car park was a 264H 50cm, put up there to increase low level coverage but was not succesful due to the fact that the anntenna design required a ground plane 5o form the beam pattern, hence all 232's and 264's were mounted at ground level. Up on top of a car park was a big mistake as the formed beam was a crock so it was short lived, it was a "told you so" moment in the engineering department.

[chevvron]

This radar business is clearly far from simple. Different towers and plinths for mounting, numerous possible sites, different manufacturers, assorted wavelengths, displays and individual nuances. An interesting subject.

I wonder if Talkdownman at Lasham would like a Watchman or S511 when the 424 eventually pegs it ?
I'm sure they'd love it at Lasham; problem is they can't upgrade their equipment too much as they'd lose 'grandfather rights' status (operating APS with A/G and without ADV/ADI).
Maybe TDM will read this and elucidate.

[Talkdownman]

when the 424 eventually pegs it ?
You mean, it hasn't?

Anyway, AIUI, w.e.f. 2020 EASA won't be permitting radar vectoring in Class G airspace. All the jets will be getting in using SkyDemon on an iPhone...if they're not already...

[HEATHROW DIRECTOR]

Dear Lord.........

[chevvron]

Dear Lord.........
You called?

[vintage ATCO]

I believe there was a 10 cm Plessey AR15 at Luton which wouldn't interface with other LATCC radars so it was just switched off and left there.

There was, god bless its valves. I held the first UK validation on an AR15 in 1974. The antenna was on a small tower but we were already over 500ft up so the antenna was angled half a degree down. Fantastic low level coverage. Great radar. We were the second airfield in the country, after Heathrow, to get SSR.

[chevvron]

There was, god bless its valves. I held the first UK validation on an AR15 in 1974. The antenna was on a small tower but we were already over 500ft up so the antenna was angled half a degree down. Fantastic low level coverage. Great radar. We were the second airfield in the country, after Heathrow, to get SSR.
Plessey installed an 'AR1b' head on Farnborough's tall concrete radar tower after the '74 airshow. This which I believe was the prototype AR15 was no good as it was too high agl and ground reflections tended to bounce up and cancel out high cover above 20,000ft; as we did area radar at the time (including autonomous airway crossings), good high cover was essential and the Marconi S232 wasn't approved for area radar use so we got our AR1 back and were never included in the AR15 replacement programme.
The AR1 soldiered on until it was replaced by a Watchman in 1991 (when they had adjusted the tilt of the aerial sufficiently) on the same tower, but when TAG took over the airfield, this radar tower was on Qinetiq property so the radar was replaced by a (in my opinion) somewhat inferior Raytheon ASR10 wef 23 Nov 2002 when we made the move to the new control tower.
The RAF recovered their Watchman for use as a spare but all the radar consoles were left in situ in the old control tower (the RAF having switched to raster scan consoles and thus having no use for them) and they were demolished with the old control tower in early 2003; what a waste; surely they could have been sold elsewhere even if only for spare parts use.

[Mooncrest]

Wasteful indeed, chevron. Like when NATS started replacing the Astrolite headsets with the Jetlite about twenty years ago. No technical advantage as both headsets used identical components. I wonder how many perfectly serviceable and almost new (and expensive) Astrolites ended up in a skip ??

I hope there is space in a museum, or outside one, for a Watchman and S511 head, when the last one finally stops turning.

[Mooncrest]

There was, god bless its valves. I held the first UK validation on an AR15 in 1974. The antenna was on a small tower but we were already over 500ft up so the antenna was angled half a degree down. Fantastic low level coverage. Great radar. We were the second airfield in the country, after Heathrow, to get SSR.

I'm no radar tech. If I'm reading this correctly, the antenna would usually be installed completely level. I'm surprised a half-degree tilt can make such a difference. Are there any downsides, such as uneven wear on the turning gear or degraded coverage elsewhere ?

[chevvron]

I'm no radar tech. If I'm reading this correctly, the antenna would usually be installed completely level. I'm surprised a half-degree tilt can make such a difference. Are there any downsides, such as uneven wear on the turning gear or degraded coverage elsewhere ?
We had to have a special mounting plate installed for the Watchman at Farnborough; actually 2 were made because the first one had the tilt wrong!

[Downwind.Maddl-Land]

Mooncrest: As an ex-radar calibrator I can confirm that surveillance radars are installed and commissioned with various Ae tilt angles to optimise their performance for specific sites and/or roles depending on the unit's Operational Requirement. Agreed, most Watchmans were commissioned with 0 degree tilt but many were +/- 1/2 degree up to 2 degrees either way.

[Mooncrest]

Thankyou Downwind. I learn so much on this site.

[chevvron]

I think it was determind on the height of the tower on which the radar was mounted; ours was quite high compared to other airfields.

[Mooncrest]

Leeds Bradford is higher still, at about 680 feet. If and when the LBA Watchman is replaced, I wonder if this will have to be accounted for. Perhaps the new Raytheon and Thales machines can overcome aerodrome elevation issues in other ways.

[chevvron]

Leeds Bradford is higher still, at about 680 feet. If and when the LBA Watchman is replaced, I wonder if this will have to be accounted for. Perhaps the new Raytheon and Thales machines can overcome aerodrome elevation issues in other ways.
I understand what you''re saying but I'm talking about height above airfield level, not amsl.

[Mooncrest]

I understand what you''re saying but I'm talking about height above airfield level, not amsl.
My mistake.

[ex_matelot]

Used to have a 'Watchman' at HMS Cambridge, Plymouth - for range safety. I think it was also monitored by London Mil.

[Mooncrest]

The Watchman must be a good machine to have such longevity. The one at LBA is approaching its 30th anniversary and has had the necessary modifications to guard against 4G interference. I wonder if there would be more of them still operational if this mod hadn't been necessary ?

[chevvron]

Used to have a 'Watchman' at HMS Cambridge, Plymouth - for range safety. I think it was also monitored by London Mil.
'Plymouth Mil' radar still operates I believe using radar heads at Plymouth and Portland to provide LARS and DACS; don't know whether they're still Watchman or its successor though.

[NorthSouth]

'Plymouth Mil' radar still operates I believe using radar heads at Plymouth and Portland to provide LARS and DACS; don't know whether they're still Watchman or its successor though.Still Watchman, and will be for the foreseeable since they're not being replaced by Thales STAR PSRs under Project Marshall.

[Sallyann1234]

I'm out of place posting here but fascinated to read your memories nonetheless.
Very sad to read the names of once great British companies - Marconi, Plessey, Cossor, Decca - that no longer exist.

[WindyMiller1]

I was leading the Watchman engineering team at Cowes when we went through the the processes of selling it to NATS. We offered our standard tower, that was in service around the world, exceeded all the requirements and looked the part. NATS rejected it and insisted on the 'scaffolding look alike' version. We hated it but the customer is always right etc etc.

[chevvron]

I was leading the Watchman engineering team at Cowes when we went through the the processes of selling it to NATS. We offered our standard tower, that was in service around the world, exceeded all the requirements and looked the part. NATS rejected it and insisted on the 'scaffolding look alike' version. We hated it but the customer is always right etc etc.
The Farnborough Watchman bought under the MOD contract was mounted on the concrete tower (much taller than the 'standard' Watchman tower) originally erected for the AR1 but initially there was some problem with the mouning plate and the tilt was wrong so the scanner had to be removed and a new mounting plate manufactured and installed.
When it eventually was available for operational use (1991?), it served us well (although its coverage wasn't as good as the AR1 it replaced) until it too was replaced by that horrible Raytheon ASR10 in November 2002 which was nowhere near as good as the Watchman.

[dukiematic]

Did you know there was an en route variant named the "Routeman"? As a spotty grad in the 90s I forgot which LRRS I encountered it at. Maybe Lowther Hill in the southern uplands. I tend only to remember the 23cm at Claxby, Lincs. Mainly because I met the nicest ever Sen Engineer there in charge of the whole site- Tony Lowe I think his name was. And the station Administrator Elaine. Made the best cuppas ever. They let us climb up the gantry with this massive rotating antenna, like the Heathrow one, only all white, what felt like inches (mm) above our heads... on a bright sunny Lincs day with nothing else around, very memorable.

[chevvron]

I always though Claxby was made by HSA, not Plessey.

[dukiematic]

I always though Claxby was made by HSA, not Plessey.

Absolutely... my point was I couldn't remember where I'd seen the Routeman because the HSA had dominated my memory, that's all :-)

[NorthSouth]

Did you know there was an en route variant named the "Routeman"? As a spotty grad in the 90s I forgot which LRRS I encountered it at. Maybe Lowther Hill in the southern uplands.Lowther Hill and Perwinnes had the Routeman until replaced by Raytheon ASR-23SS about ten years ago.