A few days ago I came to think of it, and that it would be nice with an active antenna for monitoring using my Kenwood R600. Using a Dremel-type machine I cut solder pads in a piece of PCB material. As it is only a few components it was quite easy to figure out the layout of both the antenna board with amplifier and the DC supply and filtering board.
Above the DC supply board is to the left, the white cable is a thin 50 ohm coax connection to the receiver. To the right the antenna, with amplifier half and antenna half without components.
Here is the antenna hanging in the window. It worked really good, I listened around the ham bands and heard DX from USA, Canada, Singapore and Australia on 12 and 17 meters.
Before closing this little project, I need to find something to weather proof the antenna and mount it on the roof, as well as finding a suitable box for the DC supply board.
Just a note of caution if you decide that you would like to build this or any other active antenna: The amplifier is fed with DC via the coaxial cable, make sure you check that you have blocked DC from reaching the receiver before connecting and testing it the first time. If not, you may have to experience repairing your RX!