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