[jhb_airlines] Re: Please refresh these old brain cells

  • From: "Bones" <bones@xxxxxxx>
  • To: <jhb_airlines@xxxxxxxxxxxxx>
  • Date: Tue, 23 Sep 2008 21:54:34 +0100

It's coming up to three years since I got roped in to the SBS testing and
with another unit about to be released it's getting busy again. Luckily the
software that was under development since last November has finally gone to
public beta and I've finally had a bit of a rest the last two or three

It's hard to describe the kit in a nutshell so I fear this may be a long
post. At least I'll include some pretty pictures.

Mode S transponders are slowly replacing Mode C units. This has been on the
cards for a while because we are running out of squawks to allocate to
aircraft. The future is squawkless because with the new Mode S system each
aircraft has a unique code embedded in the transponder.

With the Mode C unit you know that a pulse from a ground radar triggers the
transponder to reply. That reply is just a four digit code (the squawk) plus
height data. When we get this code our code converter replaces the squawk
with a callsign, plus anything else we might need (type, destination). In
other words the data is mostly in the ground radar databases and requires
constant updating. Aircraft showing a unique squawk like 4551 can display
the callsign on screen but the dozens of aircraft coding 7000 or 2000 cannot
be identified - we just see the height for these unknown aircraft.

With Mode S each aircraft is given a specific code which is set in the
transponder on installation - in other words the pilot can't touch it. The
whole worldwide range is from 000000 to FFFFFF with each country being given
a code block to allocate. In the UK we have 400000 to 43FFFF which we have
to subdivide for military aircraft and those of the overseas territories
like Bermuda, Cayman and the Isle of Man.

Mode S transmits little more than Mode C - code, callsign and height - but
because all Mode S codes are known it means every radar system worldwide can
use the same database to convert the Mode S code to a Registration, type and
owner. For example go to Airframes at http://www.airframes.org/ and type in
the code 400CB6 and it will give you full data on that aircraft. Peter's
C172 G-GYAV may not yet be fitted with Mode S but it has already been
allocated a code of 402991. The addition of a callsign is very useful
because most airliners have the Mode S hooked up to the FMS and so we can
see the callsign as well as the registration (if we need the latter). Other
than this basic difference Mode S is not really much different from Mode C
as it still needs a conventional radar to pinpoint the location of the

OK - take a bit of a breather...

On we go..

As Mode S evolved it became clear that the system had the capability of
sending more data than just code, callsign and height. On a trial in
Scandinavia (and another in Alaska) they fitted aircraft with extended
squitters that could send height, groundspeed, IAS, track, heading,
position, rate of climb and what the pilot had for lunch. This system is
called ADS-B and you can see its potential because it makes all ground based
radars redundant. Again, this data is sent every second and being general
broadcast can be picked up, not just by ATC but anyone with a receiver. In
the trial all aircraft had such receivers so all had a complete radar
picture of all other aircraft in a radius of approximately 500nm. Not only
that but the system was further tweaked to provide TCAS warnings on such
aircraft. Powerful stuff. Even further testing saw Mode S transponders being
fitted to vehicles that regularly move on taxiways and runways - and with
this level of use almost any airfield could operate such a system and a
Tenerife type accident would become impossible to repeat except through
downright stupidity.

So we need to know two terms here - Mode S and ADSB.

Mode S is slowly being implemented and mandatory carriage is slowly coming
in. In a sense it's daft because the CAA are way behind with their Mode S
radar installations and so all aircraft so equipped don't yet see any
advantage in having fitted the kit. ADSB isn't yet mandated for carriage by
aircraft and it is likely to be a further decade before it does. Having said
that something rather unprecedented is happening in aviation in that many
aircraft are already installing full ADSB and that before any legislation
has even been considered about fitting it. To give you an example I can
currently see 86 Mode S aircraft on my screen and 47 of these are full ADSB.

OK - that's the lecture out of the way, now on to the system.

The SBS receiver I use comprises of a decode box and a small aerial just 6"

Aerial - http://www.homepages.mcb.net/bones/WebPost/SBS_Aerial.jpg
SBS Box - http://www.homepages.mcb.net/bones/WebPost/SBS_micro.jpg

The box feeds raw aircraft data to the PC via USB or Ethernet (Wireless via
a suitable router). The software converts this to useable data and (for ADSB
aircraft) a position on a radar screen. The data flow is immense as each
aircraft sends a pulse every second. For 100 aircraft that's 360,000
messages per hour or 8.6 million per day!

The BaseStation software looks like this:


That shot was taken at 1824 tonight so it's about as current as I can get.
For a neat animated GIF from another user see

On my screen you have the radar view on the left showing all ADSB contacts
and on the right is the aircraft list showing all contacts. I'm lucky in
that I have extremely good coverage as the signals are 1090GHz and very much
line of sight - fortunately I don't have many obstacles or high ground
around me, apart from a bloody sycamore which I'm sorely tempted to
accidentally run a JCB into.

The radar screen can be set up to show many different views. If you have
good coverage you can set up several to flick between important areas or
different magnifications:

UK - http://www.homepages.mcb.net/bones/WebPost/ZMMS2.gif
Irish Sea -  http://www.homepages.mcb.net/bones/WebPost/SBSViewer.gif
Shawbury - http://www.homepages.mcb.net/bones/WebPost/ZZCL.gif
Manchester Zone - http://www.homepages.mcb.net/bones/WebPost/ZZRoute1.gif
Atlantic rush - http://www.homepages.mcb.net/bones/WebPost/ZZTS.gif
Doncaster - http://www.homepages.mcb.net/bones/WebPost/Doncaster.gif
Dublin - http://www.homepages.mcb.net/bones/WebPost/Label4.gif

Sometimes we get ducting and can see aircraft well below the nominal
horizon. Theoretically I shouldn't see aircraft over Manchester or Dublin
below 5000ft but:

Departure from EGCC at 700ft -
Aircraft on ground at Dublin -

You can also export the data to Google Earth and see the aircraft in 3D!

As I said before I have pretty good range on my system (although limited
northwards by the hills):

Range is really a factor of location and if you live in a valley or a
basement apartment in a 24 floor block of flats it's going to kill your fun.
You don't want to live in Keighley as one of our users does:
http://www.homepages.mcb.net/bones/WebPost/ZZCH2.gif - he can barely get
40nm range on his box.

I won't go into the screen display in any detail but you can see it is
infinitely tweakable. Some shots have labels on, some off. Some have a
height filter, some have four line aircraft data tags (Manchester Zone) but
others show much less information - I'm currently using just two lines to
reduce clutter.

Moving on..

The display on the right of the screen shows all current aircraft detected:

Again this table is infinitely variable and mine only shows a fraction of
the columns you can display. I've shifted columns around too so you will see
different layouts in the shot above and my current display. Note the first
column showing the symbols. Full ADSB have an aircraft symbol and Mode S
only show as a dot or four dots. After the airline logo you will see the
Mode S code for each aircraft (notice there is a miscode in my first shot)
followed by the callsign as being sent by the aircraft. 

If you double click on any aircraft in the list it brings up a further
window showing more detail. In my case I've tweaked the XML code for this to
show more than was originally provided - including pictures:

Enough of the technical side. As far as it goes I think the kit is brilliant
- I'd always hoped that ADSB would be mainstream ATC before I retired but
it's way behind schedule. SBS allows me to see what I had hoped would be the
future for ATC. I'm staggered by the range it goes out to - our Watchman
barely hits 80nm and the SBS is four times that distance. The electricity
bill between the two is laughable. The other major advantage is that the
refresh rate of Mode S is once a second -four times faster than a 15 rpm
radar head. This is a serious limit for radar talkdowns as a four second
sweep doesn't allow rapid action if things go wrong. That is why most SRA's
are terminated at 2nm from touchdown. 

In pure usability terms is the SBS a good tool for spotters? In essence (and
with reservations) I'd say yes because your spectrum of data is massively
increased and your conception of traffic flow is far greater than trying to
picture it by listening to a scanner. It's fascinating seeing traffic stuck
in the London holds
or on approach to an airport (if you are in line of sight of one). 

The real question is whether it shows the traffic you are interested in. As
a rough guide you can expect most jet fleets to carry full ADSB, especially
long haul. Short haul jets are a mix with all Ryanair, BAW, BMA, EasyJet and
European national airlines carrying it - but then you get FlyBe who refuse
to have anything to do with it and all their aircraft are Mode S only.
Likewise it's rare to see any turboprops with full ADSB, just Mode S. Light
aircraft are a mixture - many are now moving to Mode S and we see them in
the list but just as many are waiting until the final deadline before
kitting up. Having said that I notice a good dozen or so new GA aircraft
coming on my list each week. No GA aircraft seem to have full ADSB kit -
with the exception of G-BRZS, a Cessna 172 at Blackpool. I don't know where
he got the kit from but it is definitely full ADSB as I often see him
trundling over to Caernarfon from Blackpool and back.

Most military aircraft have full ADSB but they encode the position data and
we only get height and speed information - no location. They seem to be
fitting kit by unit as we suddenly get a bunch of Leeming Hawks on screen
where we'd seen nothing before. Most VC10, C130, Tornado, EuroFighter show
up now but I've never picked up any Valley Hawks or any Tucanos.

As the box is an expensive bit of kit it's important to consider your needs
before buying. If it is just local aircraft then you may be disappointed -
you won't see lots of light aircraft flying into Wolverhampton but you'll
see lots of airline traffic going into Brum. 

Bit of advice. If you are interested in the kit wait a little while. A new
SBS-1e unit is coming out in November and I suspect some users will want to
upgrade. If so expect to see a bunch of SBS Mk2 units coming up on Ebay and
this should drop the price down. 

I bet you wish you have never asked.. ;)


-----Original Message-----
From: jhb_airlines-bounce@xxxxxxxxxxxxx
[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Mike Brook
Sent: 23 September 2008 17:03
To: jhb_airlines@xxxxxxxxxxxxx
Subject: [jhb_airlines] Please refresh these old brain cells

Bones -

I've totally lost track of your extra-curricular activities re the
hardware/software tracking kit that you are using/testing. Could you please
provide a status/update regarding what it is and what is happening with it?
(If you understand what I mean ... <G>).



> -----Original Message-----
> From: jhb_airlines-bounce@xxxxxxxxxxxxx [mailto:jhb_airlines-
> bounce@xxxxxxxxxxxxx] On Behalf Of Bones
> Sent: 23 September 2008 16:45
> To: jhb_airlines@xxxxxxxxxxxxx
> Subject: [jhb_airlines] Re: Next VFR Trip
> Yes - that was bad luck. Fortunately it made the Southport show despite
> atrocious weather and also Goodwood and Silverstone last weekend.
> Luckily the Vulcan has Mode S so it's easy to keep track of. As of last
> month the BBMF also have Mode S on the Lanc and two Spitfires. I've yet
> to
> pick these up.
> bones
> bones@xxxxxxx
> http://woodair.net
> -----Original Message-----
> From: jhb_airlines-bounce@xxxxxxxxxxxxx
> [mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Mike Brook
> Sent: 23 September 2008 16:23
> To: jhb_airlines@xxxxxxxxxxxxx
> Subject: [jhb_airlines] Re: Next VFR Trip
> Following the railway, no doubt.  I was SOOOO upset not to have seen it
> t'other week at Shoreham  8-(
> M.

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