Originally Posted by
BackPacker
My guesstimate is that the problem is not in the physical size of the unit, but in the power consumption and hence the size of the battery in a non-electric aircraft.
Is there anybody who has more knowledge of electronics than me, who can do a few calculations based on power output, transmission losses etc. and come up with the size of a battery that can support a mode S transponder for a reasonable flight time (say eight hours - I understand that for a Silver C in gliding you have to do a five-hour flight)
The Trig mode-S seems to draw 6w (about .5 amp in a 14v aircraft), so if you wanted to have a 10 hour capacity you would need 60Whr of battery, A Lithium Ion battery would need to be about 0.4kg of battery (or about 10 digital camera batteries).
I am sure IO has also measured power consumption on his 330 and come up with a number not dissimilar.