See http://www.anarc.org/naswa/badx/ante...e_antenna.html

Height is much more important than length. I generally don't bother with
a horizontal run of more than 30 feet or so. For faint signal reception,
a moderate length antenna away from houses and power lines is better
than a bigger antenna near noise sources.

Peter wrote:
My backyard is limited in length. The lot is 86 feet long. My
question is,
how long a wire should I use to have a good shortwave antenna that
will fit
in my yard. I know optimum is around 100 feet but I can't accommodate
that
length. If it passes over the house does it matter how much space
there is
between the wire and the roof of the house?

-jpd