£50 Flarm receiver????

[Deker]

Flarm receiver for £50 ?
.....anyone know about this?
http://www.openflarm.co.uk/
Looks very interesting 
Deker.

[Ian Melville]

It's all kicking off on the Flyer forum again 

[Bill Maxwell]

Hmm, I became a little excited for a moment but on checking the frequency ranges in the data sheet for the Nordic radio transceiver OpenFLARM has selected, it seems that it too will be essentially European-centric. Still, interesting to watch progress.

[homeuser]

This appears partly redundant to what our beloved PAW does (sending the own position in a "simple" own protocol) - I guess we don´t want/need that especially since it means even more antennas.

Interesting is that they say that it´s legal and possible to receive and interprete genuine FLARM signals (just Rx no Tx). Since this is what probably most of want for FLARM integration into PAW, could somebody check whether this is true from a legal standpoint and if so whether it´s possible to use the same way they do to integrate FLARM reception directly into PAW?

[JCurtis]

Interesting is that they say that it´s legal and possible to receive and interprete genuine FLARM signals (just Rx no Tx). Since this is what probably most of want for FLARM integration into PAW, could somebody check whether this is true from a legal standpoint and if so whether it´s possible to use the same way they do to integrate FLARM reception directly into PAW?

There is an EU legal document relating to computer systems, possibly article 6 of the document linked applies?

http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32013L0040&from=EN

I've often wondered if someone were to open source some hardware/software to receive and decode FLARM how they would stop it, as it could clearly hinder their business model.  Naturally they could just tweak the encryption at the next annual change, they went from TEA to XTEA encryption before to try and beef it up.  However if they don't use an encrypted image to update the units it can be reversed engineered with a little effort.  The processor inside FLARM units isn't very powerful, so adding too much encryption will hinder performance.  But if they change the protocol and encryption it will mean boxes such as this will stop working until they get an update too.

This box only has a 10mW transmitter, the same as FLARM, so for "fast" moving GA the range will be very limited.  They can't legally sell this as a product without doing some basic compliance testing on not just their own board, but also the WiFi module (even though it's CE marked, that means nothing if incorporated into another system), and especially the radio module which is a cheap Chinese module you can get off eBay for £3.  Given the real core RF chip costs around £1.60 if you buy 5k of them I'd expect it to be a fake/cloned chip so who knows the stability and performance of it over time.  A couple of complaints to relevant authorities could be enough to tie them up legally and financially for a while.

The bottom line if the makers of FLARM see anything potentially hurting their business model they will take action to prevent it.  Not doing so would undermine their IP.

[exfirepro]

Also, it appears that it transmits and receives its own position signal and also receives and decodes (hacks) FLARM's encrypted signals to determine where the FLARM targets are. Apart from hacking FLARM's protocol, which as Jeremy says is pretty much inviting legal action, in order to receive both their own position signals and FLARM's, they would either need to run two separate receivers in parallel on different frequencies, or transmit their position signals on the same frequency as FLARM - which has some VERY SCARY implications!

Certainly not a route I would want to rush down.

Regards

Peter

[Ian Melville]

It also does not do ADSB, nor does it have a barometer.

[Deker]

they would either need to run two separate receivers in parallel on different frequencies, or transmit their position signals on the same frequency as FLARM - which has some VERY SCARY implications!

I think the nRF905 frequency can be programmed by a simple register write, so could be done 'on the fly' so to speak so could use a different channel to Flarm.
However, reading about the OpenFLARM project on another forum, the developers weren't aware that you can now use non certified GPS to enable ADSB out transponder.
Add to the fact that there is no barometer, I'm not sure if their subject knowledge is up to scratch, even if their soldering / software obviously is AND having another protocol is just crazy.
But £50 to RX Flarn instead of £600 for a mouse has its appeal.
Deker.

[JCurtis]

I think the nRF905 frequency can be programmed by a simple register write, so could be done 'on the fly' so to speak so could use a different channel to Flarm.
However, reading about the OpenFLARM project on another forum, the developers weren't aware that you can now use non certified GPS to enable ADSB out transponder.
Add to the fact that there is no barometer, I'm not sure if their subject knowledge is up to scratch, even if their soldering / software obviously is AND having another protocol is just crazy.
But £50 to RX Flarn instead of £600 for a mouse has its appeal.
Deker.

Indeed the frequencies are software selectable but that won't really help.  To hear either the FLARM or their own protocol you would have to flip back and forth between frequencies, each takes some time to do.  The underlying radio protocol relies on the receiver being able to determine the clock of the received signal by listening for a preamble, to recover the clock, then it will start to receive data.  If you flip back and forth waiting to listen to both you will miss data from both.

I can only assume they are going to transmit their open protocol on the same frequency as the FLARM protocol, which given the congestion people already complain about when a few gliders are in the same area will just make things worse.

They also need to read the data sheet for their processor, the decoupling and clock are an example of how not to layout the PCB.  I wonder if they have done *any* emissions or immunity testing at all?  I suspect they simply believe they don't need to, which could be an expensive mistake to make.

Personally I'd have had both the coax connectors edit on the same plane too, rather than at 90 degrees to one another, that doesn't really help package wise - but that is how those radio modules arrive on the slow boat from china.

[buzz53]

I can only assume they are going to transmit their open protocol on the same frequency as the FLARM protocol, which given the congestion people already complain about when a few gliders are in the same area will just make things worse.

Do you have a reference for this? It does not match my experience. How does Pilotaware overcome this same issue, especially given it's much greater power/range?
Alan

[exfirepro]

Alan,

PilotAware doesn't receive FLARM and deliberately transmits on a completely different frequency so that there would be no conflict.

Regards

Peter

[buzz53]

Peter,

Perhaps I was unclear. JC (who seems generally well informed) stated that Flarm suffers from congestion when "only a few" gliders are in range. He seemed clearly to be referring to Flarm alone, not Flarm shared with another system on the same frequency. This surprised me on several counts so I was anxious to learn more.

The reason I mentioned Pilotaware was that I could not see how PA, having a very similar principle of operation to Flarm, would not therefore suffer from the same problem of congestion when "only a few" aircraft were in range. Indeed, given the much greater power and range of PA it would seem the problem would be much worse. As with JCs posting regarding Flarm, this is unrelated to sharing/interworking with Flarm or other systems.

BTW can you confirm the recently published (and welcome) PA protocol document is actually current? It seems a bit ragged at the edges.

Alan

[JCurtis]

Do you have a reference for this? It does not match my experience. How does Pilotaware overcome this same issue, especially given it's much greater power/range?
Alan

I was reading around the FLARM protocol last year and despite some searching I cannot find the link to the article where it was discussed.  It came about as FLARM did not use a regular pattern for it's broadcasts, they could randomly vary from a fraction of a second up to around 2 seconds.  From memory it was the people doing the decoding who raised it (that is where I was reading around the protocol) who were seeing RF collisions on their receivers so were missing data.  This was version 4 of the protocol and it is now versions 6 so things may have changed - they did re-write the packet structure as well as moving the encryption type from TEA to XTEA.  Technically for the ISM bands you are required to have a low duty cycle, although that may depend on the ERP of the transmitter, I'd need to go an look up the regs.

PAW uses a regular transmission frequency of around 2s and despite the higher power there is little chance of a packet collisions.  In the article there was a comparison between the numbers of aircraft in any given bit of airspace, for GA flight people generally are well dispersed in comparison to gliders (not having done any gliding I've no idea if that is the case or not)  so despite the lower power of FLARM it is all they really need given it was designed as a glider to glider system. 

What is bugging me is I cannot find the article.  I remember I was reading it when I was running some EMC scans that took a few minutes each to run so I was filling in the time reading up around FLARM mulling an idea over after an e-mail I had middle of last year.  I will continue to hunt around and will post a link(s) when I find it again.

[Paul_Sengupta]

There can easily be 12 or 13 gliders in a thermal, and I've flown through an area where there were three such stacks within a very small area, so perhaps 36 or more aeroplanes all within a gnat's whisker of each other.

Even at a busy fly-in there aren't that many GA aircraft in the air at once.

[homeuser]

Well since OpenFlarm claims to be open, why not ask them how they decode and interprete genuine Flarm and why they believe it to be legal? I'd do it myself but am afraid that I could not add any value if they respond and provide technical details...