I've had a long term project which never made it to the top of the list to spend the time building- a pa0rdt-Mini-Whip LF/MW antenna, for use with a direct conversion SDR rig.
Interesting because of the small physical size - it is capacitively coupled to the e-field. This also gives it a wide flat frequency response.
The transistor footprint was flipped, but tombstoning three 0 ohm resistors and flipping the transistor fixed that.
I'm yet to get it connected to the SDR (need connector), but had it on a USB scope's FFT as a poor man's spectrum analyser. The local MW stations stood out like the proverbial dogs bollocks vs that of a random length of wire, even without a decent ground reference.
Original design details are at
http://dl1dbc.net/SAQ/Mwhip/Article_pa0rdt-Mini-Whip_English.pdf, but built with SMD and some of the parts were substituted (esp the JFETs for the front end).
Oh, I must buy some flux cleaner....