That mast does look sturdy - the gutter looks very substantial. - just needs a hinge and pulley system to the top but can be lowered to do work without taking the whole mast down

The dipole is about 5" end to end - only problem is that the feed into the dongle is coaxial (unbalanced by nature) and the dipole is a balance antenna (that's why it needs to be in free air) - a dipole really needs a balun transformer to function well. A balun for this should be really simple - just a few turns of stiff copper wir - but I'm having difficulty finding a design for one.

For new people reading this thread - have a look at http://www.rtl-sdr.com/adsb-aircraft...-with-rtl-sdr/