Yuri Blanarovich wrote:

As you start adding elements,
they add capacitance to the system and lower the overall resonant frequency
and impedance. Single Dipole is around 75 ohms, 3 el. Yagi around 30 ohms.
The more elements you add, the more sensitive the design is and requires
more prunning for optimum performance. So just slapping elements to Inv Vee
dipole will not produce optimized antenna. EZNEC, 4NEC2, MMANA are an
excellent tools to demonstrate that and to optimize the design, give you
dimensions and impedance and understanding behavior of antennas, give
current distribution in elements, plots of impedance, gain and other
parameters.


I've never seen a yagi design center frequency move any particular
direction when another element is added. I am sure you have a specific
example you can give us.

thanks
tom
K0TAR