Mark,

This month's edition of QEX (July/Aug. 2005) has an article
addressing your question with a simulation matching your
question exactly. Bottom line: put as many radials as long as
possible in your yard and don't worry about it. The simulation
with 60 1/4 wavelength radials in a 180 degree arc only resulted
in a 1.67dB difference in signal strengths from the radial
direction to the no radial direction.

73,
Larry, W0QE

Mark wrote:
Here is an additional question.

I have to mount my 40/80 vertical in a place where it can be hidden by
trees, which means against the back fence in my yard. I can only put
radials to cover 180 degrees. I assume my signal will radiate best in that
direction. What kind of radiation will I get toward the side of the antenna
without the radials?

Mark, KJ7BS