[jhb] Re: Mode S dongle.
- From: "John Woodside" <fossil@xxxxxxx>
- To: <jhb@xxxxxxxxxxxxx>
- Date: Sun, 19 May 2013 11:35:57 -0000
Mine too..
John
fossil@xxxxxxx
From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On Behalf Of
Mike Brook
Sent: 19 May 2013 07:25
To: jhb@xxxxxxxxxxxxx
Subject: [jhb] Re: Mode S dongle.
Thanks for that, John. My dongle is coming from Singapore, I ordered it on 10
May , delivery is "estimated" 21 May - 10 June!
MikeB
Sent from my iPad
On 19 May 2013, at 04:03, "John Woodside" <bones@xxxxxxx> wrote:
I’m still waiting for my dongle to arrive but I received a further post from
Jon today which may be of interest to those of you who have ordered one.
“Was so impressed with the first dongle I bought another one for use at home.
I've been running it here over the last few days feeding Planeplotter and I'm
amazed with the results considering the low cost. I did a bit of experimenting
with aerials and found the best one (mag mounted on runway lighting blank
fitting on roof of dormer window) to be the tiny 900 MHz quarter wave that came
with the foresaid dongle! Tried higher gain aerials and it may have extended
the range but I lost aircraft as they passed the west coast of the island, with
the little one I get them just fine.
Comparison right now:
SBS1e with outside gain aerial above roof line = 125 acft
Dongle with small aerial on dormer = 56 acft
Sounds quite a difference but coverage around the Irish Sea area is very much
the same.
Another interesting fact I discovered last night is that the RTL1090 receive
program is passing all of the Mode-S downlinked parameters to PP (that's
actually more than the Selex system at work does!). It doesn't display them all
dynamically on the screen but if you select on aircraft you get them all on a
pop-up window - fascinating to get a readout of the OAT + others. I've attached
four screen shots.
Will have the portable one on at work in TWR this afternoon - helps to pass
what will no doubt be a very quiet afternoon!”
Jon mentions a couple of points I’d like to expand upon.
The SBS is a serious bit of kit optimised for just one frequency so it will
produce almost optimal results. Jon says his picks up 125 aircraft and that
compares with mine. That coverage is good because we both have aerials mounted
on the roof for best performance.
Jon says his dongle picked up 56 aircraft and I would agree that is also good
reception for an aerial below roof level. My new SBS-3 is sitting here on my
desktop with the aerial in the window and it also peaks at about 50 aircraft.
Aerial location is the key. Even on a window I have found moving the aerial a
couple of inches one way or another can double (or halve) reception.
These little aerials also benefit from having a metal ground plane. Nothing
esoteric is needed here – many SBS users simply plonk the magmount aerial onto
a biscuit tin lid. It sounds daft but it works. For mobile users the aerial is
perfect if you put the aerial on the roof of the car. One of my first tests
will be to drive up near Snaefell and see the coverage I can get from up there
– if I can pinch SWMBO’s laptop..
The other point is about data. Aircraft send a lot of data in Mode S messages
and it is up to the software writer to decide which data is decoded. For the
SBS only 12 parameters are decoded – and for your curiosity these are:
Callsign
Altitude
Groundspeed
Track
Latitude
Longitude
VerticalRate
Squawk
Alert (Squawk change)
Emergency
SPI (Squawk Ident)
IsOnGround (Squat switch active)
These are the basic parameters needed for the Basestation software and are fine
enough but some users would like all data decoding – and it seems Andy’s
RTL1090 program does just that. I won’t list all the parameters but they
include Heading, IAS, TAS, Track Angle, Roll Angle, MCP Selected Altitude, Wind
Direction and Wind Speed. I don’t know the full list but it is about 50
parameters altogether.
And because a picture is worth a thousand words I will include some screenshots.
RTL1090 is the decoder program. As you can see the data is a simple tabulation
so not exciting. Once it shows it receives data I guess most people will
minimise it.
PP shows that data being displayed in Planeplotter. Jon had transposed the UK
CAA charts onto his but that is not default. I can’t remember what is there by
default – maybe just a blank screen – but you can get coastline, navaid,
airports files to add as overlays.
Posrep shows the full Mode S data for an aircraft highlighted. In this shot Jon
seems to have dumped the CAA charts and is just showing airspace and coastline
files.
No more for now. Information overload limits.. ;)
John Woodside
bones@xxxxxxx
<RTL1090.jpg>
<PP.jpg>
<Posrep.jpg>
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