Your head is empty, the frequency of your car alarm fob uses your empty noggin as a resonant cavity to amplify the signal in much the same way as the klystron in early radars thus making the signal go further
Cavity Resonator. That's it. Are you water cooled? Klystrons also on Tropo kit! Anyone come across the Yank Sig Coy the Tropoblasters? Used to go to ARRC. Remember them blasting and after about 3 days, the trees in the take off had literally browned off. Megawatt.
Polar - I think he's on about putting it up against his napper rather than arrse, perhaps it would work just as well? Try putting your head against a 2M whip when transmitting on CNR, see if you can boost the signal mmm toasty.