Is it a fact that the spectrum is available or not?
Of course it is. Every wireless device attached to your PC uses it as well
as your microwave oven.
And your long range cordless phone, and your garage door opener, and
your WiFi modem, and your wireless irrigation controller, and your local
council sewerage remote pump control system, and the local industrial
site, and your local coal/ore mine, and an underground culture similar
to CBers operating outside of the class license limitations on power &
antenna gain and so it goes on. And therein lies the problem with
operating on so called 'license free bands'.
To date the only reference that I have found on FLARM suggests that it
operates on the European 860MHz band. I don't know what arrangements, if
any, that they have made for elsewhere in the world.
It is difficult to know what is happening at the RF layer but this is
really where a system will be proven to be of benefit or just something
that sometimes works, the latter not being of much use for a safety
critical system. The brief read of the German manual via babel fish
suggests that the unit broadcasts a 57kbit packet once per second. I may
be incorrect but if anyone knows more I would love to see the information.
If the units are randomly broadcasting packets, which are subject to
collisions with other FLARM users, and you are also competing with other
users on the band then there is a better than even chance that you are
going to be missing quite a few packets which means a far slower update
rate than under ideal conditions.
Consider two sailplanes approaching an airport at a competition at
Narromine. Lots of units in the air madly broadcasting packets which are
colliding & resulting in patchy performance, the two aircraft are over
town at 1500' -> 500m, this is not far from the cloud of interference
from town. This all stacks up to provide some potential for really
shabby performance for something which is supposed to reliably assist
you in not getting your butt fried.
Be careful of what you allow to get started as you may be stuck with it
regardless of the sense of replacing it with something better. AM
modulation on VHF comms and transponders being two that fly to mind in
aviation.
A more useful direction would be to actually set a goal for an
inherently robust system & work toward something that actually fits the
requirement instead of falling provably short. Something targeted at
sports aviation, and specifically roving clusters of sailplanes stacked
in thermals, with a more reliable level of communications performance.
In short, something that will be taken seriously by Civil aviation
authorities.
The task is not impossibly complex nor is it prohibitively expensive,
but it does require a sense of commitment & co-operation from the bodies
involved. Supplying governments with a robust engineering solution to
the sports aviation problem may just provide the push to actually solve
the problem as opposed imposing the current ADSB system as though it
might actually help.
Otherwise you end up with the current fiasco at airports, it costs
money, keeps people happy ( those who don't want to look behind the
curtain) but doesn't actually do anything fundamentally useful as far as
ensuring a greater level of safety. Statistically it increases the level
of safety by reducing the incidence of easier cases ( killer
grandmothers with nail clippers but still allows major show
stoppers ( fundamentalist nutters with polymer firearms and ceramic
knives ) to get thru.
A quote from the FLARM homepage:
>> Flarm warns of collisions
>> Collisions are the secondary most important cause of accidents.
Flarm >> warns of other flying objects equipped with Flarm and cables
>> (obstacle map of Switzerland).
It is the cable issue which is greatly assisting it's uptake & this is
relatively robust providing the obstruction map is kept up to date.
The RF side of the system should be carefully questioned prior to it
being allowed to get any serious market hold.
To fully understand this situation it is necessary to have helplessly
watched some really seriously expensive and very large radio controlled
equipment tear itself to bits when the "secure error corrected link" was
taken out due to interference which, according to the clients IT boffin,
doesn't effect spread spectrum systems. Fortunately it wasn't one of
ours so we got to have a good giggle.
If someone is going to start using something suggesting a level of
safety or protection as a result of it's usage ( even just augmenting
the existing visual airspace scan ) then I would like to at least be
confident that when required that it will be capable of performing as
required.
If this sounds like tearing down something without offering a solution
then I would be happy to supply a draft of a system proposal for the
said RF layer. I must caution however that it is at a very early stage.
If at the end of the day there is far more to the FLARM RF layer and it
is able to reliably handle a large fleet of aircraft during a comp, in
the presence of severe ground borne interference, then I shall have a
feast while eating the above ;-)
Cheers
Don Ingram
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