Doesn’t the antenna need to be vertical?
I saw one ADS-B receiver installation which had a ~30cm vertical rod and could pick up ADS-B over a radius of a few hundred nm.
alioth wrote:
why would a glider be carrying a 2m long very directional flarm antenna?)
Because a racing task is up-front assigned therefore all competitors are flying in the same direction. Information who is far behind you is not really useful
Despite is one of the major concerns while flying, I will be waiting for better and feasible solution for collision avoidance systems.
Thanks for all the knowledge bought into the discussion.
Having thoroughly confused myself reading all this, I’ve put together a quick summary of the options here: https://docs.google.com/spreadsheets/d/1Q_SplMSdkDMZDUztjH7rUj0VnE3GobQxIegmLeiP57Y/edit?usp=sharing
very useful document!
I would add Openflarm to the list – it’s not there yet but hopefully it would be a viable option. Projected cost is 50 pounds
As the Pilotaware is concerned one should not forget about yearly subscription / renewal fee and the fact that the protocol itself is proprietary. In theory this means that the fee might be changed over time and users would have limited options.
Robin_253 wrote:
Because a racing task is up-front assigned therefore all competitors are flying in the same direction. Information who is far behind you is not really useful
But if everyone’s carrying 2m long yagis in their gliders, then no one will have any information: if you’re using a directional antenna to find out who’s ahead, your yagi must be pointed forwards, and if everyone’s yagis are pointing forwards, they will only be radiating FLARM signals forwards (so competitors behind won’t be able to see who’s ahead). Unless you have two FLARM systems and two antennas (the standard 1/4 wave for the FLARM you’re using for anticollision and to transmit your position, and the yagi for receive only). If it’s a 2m long vertical then it really won’t have much benefit over the quarter wave vertical or a half wave dipole.
@Robin_253 I’ve added OpenFLARM. Frankly, while the cost is good, and I welcome a competitor that can read FLARM, do we really need another non-standard protocol?
Peter wrote:
I saw one ADS-B receiver installation which had a ~30cm vertical rod and could pick up ADS-B over a radius of a few hundred nm.
A long antenna which is a vertical will have some gain horizontally at the expense of being less efficient for higher angles. With ADS-B (mode-S extended squitter) this is probably not such a huge issue because the transmitters are fairly powerful, and so you might want some horizontal gain to be able to see out further since the signal will be strong enough from nearby aircraft far above the horizon to overcome the poor performance of the antenna for receiving transmissions that are from higher above the horizon.
However, what surprises me is a 2 metre plus long antenna in a glider which must – due to size constraints – be horizontal (unless it’s a 2m vertical sticking out the top of the fuselage). If it’s a whip laid horizontally, it will have terrible performance for seeing FLARM targets ahead or behind and it will have the wrong polarisation – all its gain is perpendicular to the antenna, so up and down and to the sides and given how low power FLARM transmissions are, it won’t see much forwards or aft at all. If it’s a yagi, then it’ll be highly directional whichever way it’s pointed (forward in this case) and probably not so useful for its primary function: collision avoidance.
alioth wrote:
probably not so useful for its primary function: collision avoidance.
Obviously collision prevention is not something you think about then building a tool which will give you advantage in racing. I can’t comment on theory behind this particular antenna design. I don’t have any hard evidence to back up claims about it’s performance either. Owner / pilot / inventor of this solution is happy with what he has and the alleged detection range far exceeds what a standard Flarm antenna can give you
jwoolard wrote:
do we really need another non-standard protocol?
Bill Gates might have asked the same question a few years ago: We have the internet explorer, do we need another browser? 
I would rephrase your question: " do we need an open protocol?" In my opinion YES
AFIK neither Flarm nor Pilotware has published their respective protocols.
I would rephrase your question: " do we need an open protocol?" In my opinion YES
AFIK neither Flarm nor Pilotware has published their respective protocols.
I completely agree. We need an open protocol, which everyone can talk, and we need a relatively low cost implementation of it. Luckily, such a protocol exists, and we’re starting to see low cost products using it: ADS-B
