More information at http://www.eh-antenna.com/
I built one for the 30 meter band. The antenna is about 2 feet long, and have the antenna resonant close to the 30 meter band. According to my SWR meter, it currently runs about a 2:1 SWR on 10.139 MHz. I could get the swr down even lower by adjusting the matching coils. I did a rough tuning on mine, and got it close enough for now.
I've read mixed reports by hams who have built these antennas for themselves. Many say they dont work. Here is what I've found so far:
On receive, it seems to pick up a fair amount of noise, but that could be due to antenna placement. I dont have the antenna up very high, only about 10 feet.
On transmit, it appears to do fairly well, even at this height. Signal reports are about even using WSPR. I chose WSPR as an antenna testing mode because every station "advertises" their transmit power, so I can compare transmit vs receive efficiency easily. There is a difference, as my untuned 20 meter hamstick (going thru a tuner in the shack) consistently runs about 10 dB weaker on transmit than in my receiver.
Although this is not paint a complete picture, it does tell me that it works equally well, (or equally poor) between receive and transmit. When I am able to test the antenna when its up a bit higher, I'll be able to make better comparisons.
Watch for me on the 30 meter WSPR freq. I'll be beaconing using this antenna for awhile.