Hi fellow SafeSky users. This question is slightly off-topic but still I hope someone can shine a light.
I rent a plane that is equipped with a fancy Garmin GTS800 TAS.
That device searches the sky for other planes and creates a picture of planes in the surrounding. The user manual is full of terminology that I cannot always understand. My question to you is “which planes will be and which ones will not be discovered”.
I can understand how it detects the position, altitude, speed etc of ADS-B equiped planes.
Bu if someone in the surrounding does not have a ADS-B transponder with coupled GNSS, but only has a Mode-S transponder, will the GTS800 TAS discover the relative position of that plane?
If so, how can that achieve that?
It seems to actively interrogate transponders in the area, but a Mode-S transponder will not respond with position info.
So perhaps the GTS800 might use a directional antenna that tries to calculate the bearing of the Mode-S equipped aircraft.
And it might try to calculate the approximate distance based on the power level of the received transponder signal.
Sorry if this question is too much off-topic.
Ans thanks if you can explain how this works.
Hey Robert,
If I understand the GTS800 specs correctly it uses directional antenna(s) mounted either on top of the fuselage or on top and bottom of the fuselage and is capable to actively interrogate a Mode-S transponder and receives either GPS position from ADS-B out or is capable to calculate direction and distance from responding Mode-S signal as well as coded (baro) altitude.
@tgebhard distance and exact location would still be somewhat of a ‘guess’, right? Since it does not get a accurate position from GPS, it has to get the location from the phase difference between both antenna’s to get a bearing, Baro altitude?
Garmin specs of the standard antenna talk about a 50ft accuracy when processing a Mode-S reply within the coverage range. The (baro) altitude information of the target is encoded within the transponder’s reply.
yesterday I spoke to an engineer who explained the mystery:
a Mode-S transponder, when interrogated, has a well-defined time lapse for sending the reply. So the GTS 800 measures the time between transmitting the interrogation and receiving the reply.
Relative position is indeed measured with a directional antenna.
Thanks for the folks from SafeSky for delivering a same or better solution, including FLARM, for €30
SafeSky is certainly not better for mode-S tranponders, as I exprienced.
A good TAS800 setup has directional antennas both at the roof and at the bottom of the aircraft.