[Antennas] Half-Square Question

[Robert Lay]

Dear Ron,

There may be a better way to explain this, but  here goes:

The thing that probably worries someone about the connections from center
conductor and the shield of coax is that they want to believe that the coax
shield is everywhere at ground potential.

Keeping that in mind, let's look at the potential of a point in an antenna
system that is 1/4 wavelength from an open end. The laws of physics tell us
that at 1/4 wavelength from the open end of the antenna, we have a minimum
voltage. I.e., it may not be zero, but it will be a minimum on that antenna
system. By the same token, a point that is at any odd multiple of 1/4
wavelength from an open end of the antenna system will also be at a minimum
potential.

Therefore, in the half square, it really doesn't matter which of the two
conductors of the coax go to which leg of the half square, because from
either end of the antenna back to the coax we have an odd number of 1/4
wavelengths, and our potential at each of the two feed point terminals is at
a minimum with respect to earth. So, a given designer may have some
preference for which terminal he will connect to which terminal of the coax,
but in theory, it should make no difference.

Bob Lay (W9DMK) in Dahlgren, VA
http://www.qsl.net/w9dmk