Back to Cusco's question - if the transponder gets its info from an altimeter on your panel, that altimeter will have the word ENCODING printed on the dial (well, all the ones I've flown did).
I was a radio amateur from a tender age, forced to use morse cos I wuz too poor to buy a microphone and build a modulator, and I think Q codes are wonderful .
QNE is worrying - it means "field elevation shown with 1013 set" (sometimes called pressure altitude), but I often read postings from people who think it's the Q code for "set 1013" rather than QNH or QFE.
Like many, I was brought up to use QFE for takeoff and landing and QNH for everything else. IFR training in the USA soon cured me. QNH on both, and cross-check. Or 1013 on both, ditto. Close to trans alt/level and I'll have one of each. Each to his own, I suppose.