The Slinky antenna is a variation of a shortened spiral dipole, where metal springs are used instead of a standard straight wire. I put together this design a couple of months ago, because I live in an apartment and there is simply no way to stretch a normal dipole on the roof. I spied the idea and basic dimensions in the material on the Slinky Dog Antenna, where everything is described without unnecessary theory. I used two steel springs, connected them through a balun and stretched it straight along the balcony. It works great for reception, it is even a little less noisy than a regular long wire. For urban conditions and limited space, this turned out to be a really working and very budget-friendly way out of the situation.