Robin_253 wrote:
Besides you might be willing to turn off your transponder while flying through some airspace and at the same time leave your Openflarm ON. What would you ay about this use case?
It’s illegal for one. Transponder, if installed, must be on at all times, regardless of airspace. I think this Open FLARM looks good. I’m sure going to install one when they come out. If I understood it correctly, the device will detect all FLARM devices? but the newest closed FLARM devices won’t be able to detet Open FLARM. That is more than good enough for me. Just hope that someone makes a small unit with a tiny AMOLED display, to be put on top of the panel.
Transponder, if installed, must be on at all times, regardless of airspace
We have a thread here on that and it produced some heated debates 
Of course I think it should be thus, but many people differ, especially on “civil liberties” grounds… @mh had a strong view on that, I seem to recall.
What would you ay about this use case?
If I was ATC, and reading EuroGA as most of them are, I would get a FLARM receiver and bust those people who are busting CAS. It would be easy – very good altitude data
Peter wrote:
I would get a FLARM receiver and bust those people who are busting CAS. It would be easy
Easier said than done am afraid. Flarm is low range and to make things worst, at the moment AFAIK Openflarm protocol is (for unknown reasons) not implemented / accepted by people behind glidernet. So the only way for ATC to spot you would be by sentries flying helicopters around. Kind of like trying to shot down a stealth aircraft. I know Serbians did it, but it takes respectable skill, expertise and intel.
LeSving wrote:
It’s illegal for one.
Of course it’s illegal! But some people do it. And even more people decide to fly without any transponder just to avoid cost and hassle.
Easier said than done am afraid. Flarm is low range and to make things worst, at the moment AFAIK Openflarm protocol is (for unknown reasons) not implemented / accepted by people behind glidernet. So the only way for ATC to spot you would be by sentries flying helicopters around.
One can do a great deal to receive weak signals. If you are talking about FLARM emitters flying with the TXP turned off around the base of some TMA, busting the TMA from underneath, you don’t need to be receiving the stuff from say 50nm away. You will also have a primary radar return so a directional antenna could be employed.
Kind of like trying to shot down a stealth aircraft. I know Serbians did it, but it takes respectable skill, expertise and intel.
I am sure this is on wiki somewhere but think they did it with a bit more than picking up weak emissions. If you can pick up a FLARM emission, you have everything there including the 3D position.
Just a small point, my PowerFlarm installation has top and bottom external antennas and that seems to make a large difference. I was told by my supplier that most gliders have something velcroed on the dash or poor installations – but of course it is fine for them as they are just trying to avoid their mates in the the thermals who are a few hundred meters away.
I can detect gliders from 8 Nm away but if i am detecting one glider, as they spiral up, I often lose the Flarm transmission as they turn (as the power out is 10 Mw it tends to radiate well through the Persex screen but absorbed by the Pilot/Fuselage at larger distances). If I am closer these “drop outs” do not happen. To put this into context your DECT cordless phone at home has more peak power so you do need decent external antennas for best results.
It would probably be possible to make a Flarm Transmitter to sit on the dash for £ 100 in bulk – that would work well at 3 Nm – I know I keep going on about it but I’d make it mandatory to have either Flarm or a transponder with ADSB out). Then it’s up to people to decide if they want to spend more money for a display!
I’d also deal with the Civil Liberties stuff by making it possible for a pilot to request the deletion of data from Flight Radar 24. I agree with Peter, his active system will detect far more than PowerFlarm but it is truly shocking how much stuff pops up on the display that you never see.
FR24 is however not the only site. There is a bunch of them e.g. this one and anyway anybody can set up a receiver (ADS-B goes a very long way and can be picked up from hundreds of nm away with some decent electronics) and upload the data to a server and nobody can do anything about it especially if the server is out of the EU jurisdiction.
I reckon 75-90% of targets I see on the TAS605 will never be acquired visually no matter who is in the cockpit. But the worst are all the non-TXP people (a few of whom are technically justifiable) and the Mode A people (none of whom are justifiable at all).
Archer-181 wrote:
I was told by my supplier that most gliders have something velcroed on the dash or poor installations
I’m afraid your supplier doesn’t have up to date informations. I saw glider Flarm antennas 2+ meters long and other fancy gizmos which allegedly improve detection range. The reason is because Flarm is quite often used to get tactical advantage during competition flying. I heard stories about detection range going up to 20km after such upgrades.
What does the receiver antenna look like for the 20km range? Presumably in this case it is airborne also, and then how is the equipment used?
The simplest setup I saw was a long antenna placed on the bottom of fuselage. The wire was inserted underneath pilot’s seat and going up to instrument panel. Of course this would only be working in fibreglass structures.
As to how it is used: Initially Flarm was conceived as a collision avoidance system but fairly quickly people discovered that in a gliding competition data transmitted by Flarm is gold. I can simply glance on screen and instantly I know: who you are, where your are and if you’re getting lift or sinking. If you are getting stronger lift that I am, I might follow you to take advantage of the superior conditions you enjoy, if you’re sinking I know where the downdrafts are and which places to avoid, if you are one of world champions I might decide to follow you regardless of your present situation 
Robin_253 wrote:
I saw glider Flarm antennas 2+ meters long
A 2 metre long flarm antenna sounds a bit silly, IIRC flarm uses the ‘keyfob’ frequency which is in the 70cm band, so a resonant half wave antenna is only going to be about 30cm long. A 2 metre long antenna would be inefficient with much of the transmit signal just getting reflected back into the transmitter, and also not the best receive antenna (unless you’re just talking about the boom length of a yagi, but these are directional and one with a 2m long boom would be very directional – why would a glider be carrying a 2m long very directional flarm antenna?)
