One thing to be aware of with a really long wire antenna, is the tendency to overload portable shortwave receivers. Simply put, there's too much signal for the radio to efficiently handle. The result is phantom signals from more powerful broadcasters appearing as ghostly echos throughout the shortwave bands. I experienced this many years ago when I used my Sony ICF-2010, an excellent portable in it's day, with an outdoor long wire antenna. That's why I suggest limiting the wire length at this point. Also, if erecting a horizontally-mounted outdoor antenna yields too much interference, you may try reorienting the antenna in a different direction, if you can.