E field probe... my two systems use a 35mm and 15mm respectively. A metal pop bottle cap will work fine.
H field: My Red uses 2 homewound 300mm x 7.5mm ferrites @ 90°. Blue development 3 DELTA (60°) 250mm X 7.5 mm ferrites..
Operators use every imaginable kind of loop, from 12" Balls, to 5 Feet coax loop, Mobius, etc... Antennas are unturned.
Our spectrum of interest is generally 3-30lHZ where most impulse energy resides...
BLUE Systems have "functional" bandwidth up to ± 300kHz, filter restrictions are in preamps, and amplifiers...(BLUE has optional electronic filters) not necessarily 'antenna design'... in addition to trigger settings etc... just don't want antennas that induce long delay times.
Hams have had little issue running BT and Ham ... our issues are robot mowers, pet fences, light dimmers, plasma TV's street lights, auto ignition, computers too near, cheap-a**ed power supplies, solar power systems... blah, blah, blah....
It some respects, I still say
it may be simpler, at times, to think of BT as wideband "audio" impulse processing, rather than "RF".... In other words, if it bleeds your audio system, it'll bleed Blitzortung... now, here's where the usual or unusual few will jump in to tell me I don't know what the hell I'm talking about...