On Tuesday, May 22, 2012 4:57:58 PM UTC-7, Morgan wrote:
I can only report on what our experience was. Both the towplane and my glider had a PF portable installed. Of course, with the towplane 200ft in front of me it may have been transmitting but not a threat.

My flarm was using the flat panel antenna that came with it. The other glider was using the standard stub antenna so a difference in reception sensitivity or transmit efficiency seems plausible. Additionally, my antenna was on the right side of the aircraft and the approaching glider was quartering head on from the left. So attenuation through my thick head was certainly a potential as well.

Despite imperfect performance I'm finding the device really useful and worth every penny. I'm very confident that the flarm team is on the right track regarding performance and it may just be a matter of time and field trials to knock out the specifics and help provide the best ways of mounting antennas and such for maximum range.

Morgan


On Tuesday, May 22, 2012 4:39:24 PM UTC-7, Bart wrote:
On May 22, 3:48*pm, Chris Nicholas wrote:
To my simple mind, for you to get an alert, your PF antenna and the
glider’s PF antenna both work on line of sight, so each has to see the
other. It should not be a one way street.
I suppose it is possible that in one direction the signal was just
strong enough and/or not too badly attenuated, and the other less
good. What do the experts say?

I am hardly an expert, but... yes, an antenna is exactly as effective
while transmitting as it is while receiving. The attenuation
experienced by signal from glider A to glider B is exactly the same as
the one experienced by signal from B to A.

My guesses, in no particular order:
1) Either transmitter power or receiver sensitivity differs between
units. The pilot with less power or more sensitive transmitter will be
the first one to get a warning.
2) One of the gliders has a lousy (noisy) electrical installation.
This effectively decreases receiver sensitivity.
3) One of the antennas is so bad that the transmitter reduces power to
avoid damage (and no, this does not contradict what I wrote at the
very beginning).

Bart

Morgan

I'm surprised others have not asked this yet but to be clear - you had the flat antenna connected to the "FLARM A" connector right? The "A" connector is transmit and receive, the "B" connector is receive only. The flat antenna is normally connected to the "B" port as a receive only diversity antenna.. If you incorrectly had the flat antenna connected to the ADS-B "B"connector and nothing on the "A" connector you will be receive only and that would of course explain why you saw a threat but another glider did not see you. If this was the problem it would be nice to followup with a nice warning on ras for others.

And in general you might be better off using the standard helical antenna (if it will fit with the antenna vertical). The small flat antenna and relatively long thin cable has got to add more loss here compared to the helical (which may be slightly higher gain antenna that the flat one anyhow - but I don't know either antenna specs).

If that was not the problem, then as Bart says the reciprocal principle means that an antenna (or pair of antennas) behaves the same transmitting and receiving. So the loss paths both ways should be the same. The guesses as to what might be happening look good to me as well...

Either way its great to see PowerFLARM being used at the Avenal contests and more pilots getting exposed to its benefits.

Darryl