Planeplotter [PP ] has the ability to assess the rotation speeds of the radar heads in addition to seeking out their approximate location.

What is interesting is that the rpm we are seeing , estimated to three decimal places , varies quite considerably from site to site.
Most are rated 15 by NATS , however none are exactly that figure , tending to be between 15.2 and 15.8

I wondered if perhaps the rotation is checked and calibrated on a regular basis.
Is the true rate exacly 15 and are the variations artifacts of the PP software or do they really rotate at varying rpm ?

The longer the range for the radar to 'see', the slower the rotation rate. Most en-route radars rotate at around 7.5 RPM (individual sites range from 7 to 7.6). Shared en-route and airfield facilities will be in the order of 10 RPM (sites range from 9.72 to 12). Radars primarily used for airfield ATC will be in the order of 15 RPM (sites range from 15 to 15.7).

The exact rotation rate is known and controlled by the ATC control and monitoring systems and the RPM will not vary considerably as you state. More likely that the inaccuracy lies with the 3rd party software being used to work it out for the non ATC application you illustrate, which is not required to have the same accuracy as a regulated ATC system.

Its not really that inportant how accurate the RPM is, just so long as we know exactly where it is. Each rotation is digitised into 4096, reset at the North marker. If is doesn't count 4096 between Norths' then it throws an error. The RPM will change slightly due to wind loading, you can hear the head straining into the wind on a blustery day.

In the US overlapping approach radars will operate at different rotational speeds to prevent false locking of targets (not much different, just different)

Again , many thanks for the flow of info

10W , the rotation rate details are excellent , thanks.
This is all an unexplored area for us and the data here is helping to build the picture.

Tigersaw.... I have been experimenting with rotation against location and it confirms your comments re exact location....in a simlar way that for Planeplotters multilateration system we need pinpoint accuracy for our ground station location [ of which we now have over 300 ]

MarcK . . . I know our US users are having some difficulty . Whilst an FOIA revealed the site locations State by State , they are struggling with a lack of SI/II data.


Back here in the UK , some observations.

From our findings it seems that some Mode A/C sites are only operational at certain times.
I have an unknown site near Teeside which for example seemed to close down at the weekend.This leads me to think its possibly a little further south than I thought and may be Leeming

Some sites , such as Clee Hill give poor results no matter what we do . I suspect CH may be a cluster type array.

John

Clee 52 27 19.767 N
02 35 57.997 W Is that accurate enough for you? ;)

It's a Raytheon MK2A LVA Mode S Enhanced (dual channel) turning at 7.5 RPM on frequency 1030 Mhz.

BD

Many thanks BD

Thats the data I have , gleaned from our own survey . It uses the ident II 05 , but beam results can be a bit erratic which leads me to wonder if its used as a cluster site .
Surprisingly a/c only seem to respond to its interrogation when over the Scottish borders.

Sorry to be pedantic but it's Teesside. At the side of the Tees not the Tee.

A proper pedant would point out it was Durham Tees Valley Airport :)

No! To locals and those who work there, it's Teesside!

Ah,
RAF Middleton St. George.
Route direct to the Tango Delta. :ok:

So...is my unid Mode A/C radar head Teeside...Teesside .... Durham Tees Valley Airport....or somehwere else..? :ugh: :)

According to their company website, DTV Airport use a feed from Great Dun Fell and don't have their own SSR. I believe RAF Leeming do have one however, and it might make sense that it is turned off when there is no fast jet flying at weekends.

And the geography of that bit of the Pennines means that you can almost see the ground at Teesmouth from the top of GDF!

If you are building a "unique multilateration system", why do you need to know the position of interrogators? Other multilateration systems are able to use unsolicited replies without any knowledge of how they have been triggered or where from.

PlanePlotter already has a unique Mlat Wide Area network complete with its own Ground Stations , now numbering over 350 , across the UK and Netherlands.Thats been in place three years and works remarkably well.
Its also infinitely cheaper than NATS own very limited Mlat system , recently set up in the N Sea :eek:

However as the Mode-S messages carry the ident of the interrogating radar head we are now developing a further system which will support
Mlat in fringe areas.
We are also using Mode A/C pulses to add a second layer to this system.

Finally , by converting the Mode A/C data from non mode-S equipped a/c to sqwks we can then use those to attempt to locate Mode A/C only a/c too by comparing the pulse rates to those associated with Mode A/C ground stations.

I don't suppose a spotter's network like PlanePlotter has to worry too much about CAP670 and the various other regulatory requirements.

BD - you should know better!! :=

NATS doesn't give out the positions of the radar sites to anyone without a legitimate regulatory, security or safety reason. A FOIA request I suspect is pointless as NATS is a commercial company, not a government agency.

I would also suggest monitoring NATS transmissions for purposes they are not intended and using them for other applications, whether radar or voice, is probably not legal. See the sticky on the Main ATC front page http://www.pprune.org/atc-issues/206...tions-law.html

Given that Mode A/C only radars have to be turned off by the end of 2011 in the UK (be interesting to see how the CAA make that happen given UK MoD are massively behind), any system relying on Mode A/C is probably going to be of diminishing use.

But good luck :}

RS

Lets see what the CAA come up with

They have been prepared to give full information , including rotation speed and exact location of the sites in Scotland regarding the effects that wind farms might have on radar returns and that info is in the public domain.
Anyone with a GPS and a map can go and get a precise reading for each one....if they have the time , and also measure the rotation rate.
There are already NATS/CAA documents which give details of SI /II codes......its just that there isnt one definitive document listing all

As requested under FOIA 2000 regs the CAA has now provided a full list of UK radar stations including rotation rate SI/II whether Mode-S or Mode A/C [ or Both ] and exact location to 14 decimal places.:ok:

Now we can move on to the next phase.