ATC Radar Ranges in 2014.

[phiggsbroadband]

Hi Guys, just to give you some background details, I was employed by BT (The GPO.) many years ago and got involved with the Three GPO Microvave Links between Birmingham and London (six 10ft dishes on several masts.) These were use to relay the raw PPI green traces from the Midlands to London.


So I suppose that technology has advanced a lot since we de-commissioned that equipment... The question is... Do you still have screens dedicated to just one radar head, or is it digitally mastered to be a selection of whatever radar-heads you require for your sectors?

[Una Due Tfc]

Multiple simultaneous feeds from numerous different SSR heads on the screens I use. I'm told if 2 aircraft came within about 1.5nm at the same level, the traces blur and become difficult to distinguish, but if 2 aircraft at the same level were that close, you would have far more serious things to be worrying about.

[HEATHROW DIRECTOR]

When I was at LATCC (retired 2002) we could select any of half a dozen heads to display but I suspect this is different now. It was great fun winding Clee Hill out and off-setting it so we could see Concorde coming in off the Atlantic. Radar displays now are largely digitised and the last ones I used weren't green.

[Plazbot]

I am guessing most if not all radar positions use multi radar tracking and without a minimum number of feeds, min sep must be increased. One pretty interesting development these days is WAMLAT. It uses a known signal be it a radar, radio wave, tv station and via ground based receivers plots a position. Pretty cool stuff. From the one installation I have seen, it is certainly not operationally ready but is pretty close. I believe it is in use certain in parts of the world.

ADSB is another. Extremely accurate via calibrated receivers and work stations and is being used in many parts of the world for Radar sep standards.

[phiggsbroadband]

Thanks for the replies, and Ok on how possible position errors are ironed out by the software engineers. I think our GPO microwave links were first replaced by co-axial links then obviously by the fibre optic land-lines...

In the old green dot days there used to be the anomaly of slant range to be taken into account. So for instance, two planes that where one above the other ( at say 1000ft and 40,000ft.) It appeared the higher plane was 1 mile behind the lower plane, because of it's increased slant range. I think there were other aliases caused by pulse lengths that also could create other types of errors.


Must admit I know nothing of software engineering, but I still have my inch and an eighth whitworth spanner and my climbing harness, which have been gathering dust over the last 20 years.

[Plazbot]

So then what is your question?

[Capot]

Going back to the original question, I guess range is what you want it to be; following installation of a Watchman in the mid-1980s our air traffickers were able to watch traffic within 40-60 miles on primary data (distances fogged by memory) but also traffic landing at LHR, 200 miles away or so, on secondary data displayed on the same screen. Moreover they could centre the screen on LHR.

So how would you describe the range of that system? By reference to the primary data only, or by reference to the secondary data that was fed to it from another radar?

[Capot]

Going back to the original question, I guess range is what you want it to be; following installation of a Watchman in the mid-1980s our air traffickers were able to watch traffic within 40-60 miles on primary data (distances fogged by memory) but also traffic landing at LHR, 200 miles away or so, on secondary data displayed on the same screen. Moreover they could centre the screen on LHR.

The secondary data were processed in the Watchman for presentation on the display so that the horizontal position of the target was displayed correctly.

So how would you describe the range of that system? By reference to the primary data only, or by reference to the secondary data that was fed to it from another radar?

[phiggsbroadband]

Hi Plazbot, I was just thanking you for the replies to my OP so far.


It appears that most NATS radar units now use computer type monitor screens, and are capable of displaying any part of GB that takes their interest...
However I know that some Radar ATCs (including military units) are still less technologically advanced... I have been asked, whilst flying with Mode S, to report my position, which they obviously had not seen on their screen.
So I would think some are connected to the WWW and others are only connected to their rotating radar heads.

[Capot]

I suspect it's not the WWW but the modern version of what I was describing from nearly 30 years ago; to minimise the amount of SSR interrogation, SSR data from one or more radars within, say, 100 miles of a radar was fed to a radar display by landline, and was then processed and displayed on the trafficker's screen with the primary returns generated by the short range radar at that location.

The main point was to enable the smaller radar to capture and display the SSR data which it would display with the primary returns it could see. Outside the actual range of the radar all that could be seen was the secondary data (ID, height etc) against a target position marker.

[FantomZorbin]

phiggsbroadband


I would imagine that, by now, radar data is available via satellite links etc. so the ranges would be indeterminate/unlimited; however the data rate might be limited.

[HEATHROW DIRECTOR]

If by WWW one means the Internet, I don't think any ATC radars depend on either the WWW or satellites!

[eglnyt]

Whether or not they use the Internet depends upon your definition of the Internet. They are networked using similar protocols. They do also use satellites but mostly for timing rather than data transmission. If the OP does a Google or Wikipedia search on RMCDE there is plenty in the public domain to explain the technical workings.

[phiggsbroadband]

Hi H.D.... well maybe not www, which is in the public domain, but as Lookingforajob says OLDI.. On-Line Data Interchange, which would come down a fibre optic cable and not via our old GPO microwave links.


btw.. I ended up having one of the 10ft dishes in my back garden, I used it at the start of Satellite TV, and also for Meteosat weather pictures (now available on-line.)

[HEATHROW DIRECTOR]

Ah yes... RIG! Seems to have disappeared now.

[FantomZorbin]

... perhaps I should have included a "," between "satellite" & "links" in my post. ;)

[phiggsbroadband]

Hi FZ, well I suppose it would be a good idea to have Satellites that search out SSR radar returns, that would stop all us GA types hiding in valleys where we are out of radar detection range.

However I think most of our SSR aerials are on the underside of the fuselage, so maybe the signal would not even reach a satellite.


btw.. HD, I had a 1m portable dish with the R.I.G. 64Kb Framestore, and used to give demonstrations of Live Meteosat Pictures to Schools, W.I's., Rotary Clubs and National Trust events. Even had the Look North Weather Presenter make a TV clip of the big dish set-up, must have been about 1988.

[Lon More]

Try Wiki on RMCDE (http://en.wikipedia.org/wiki/RMCDE)

[foghorn]

The standard radar picture at NATS centres is a "tracked" picture (plots from multiple radar heads "fused" into one track based on whizzy mathematics in a computer at the centres). Single radar sources can be selected at the controller workstation if necessary.

The data travels from the radar sites to the centres over Internet Protocol (IP) network links back through a private Multi-Protocol Label Switching (MPLS) "cloud". This is bascially the same MPLS network operated by phiggs' former employer, that phone calls and the public internet go through, however with some special requirements placed on it because of the criticality of the data.

NATS has done a lot of work in the last few years moving from expensive copper point-to-point "private wires" and old network protocols to modern cheap IP/MPLS links. it's not an easy job when you realise that NATS needs high grade comms links in places where nobody else needs to share them. How many Hebridean sheep need a 99.999% available network connection with guaranteed diversity to the self-healing core?

[Inner_Ninja]

How many Hebridean sheep need a 99.999% available network connection with guaranteed diversity to the self-healing core?

Only when they're trying to buy inflatable humans on eBay......

(Sorry, couldn't resist. Back to the topic at hand.)