Yuri Blanarovich wrote:

"Tom Ring" wrote in message
.. .

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


No problem,
go to EZNEC, load NBS Yagi example
3el. resonant around 49.95 MHz
take director away, 2 el. resonant around 49.30
take reflector away, dipole left resonant around 51.05

You welcome

Yuri, K3BU



Ok, that clears it up. You said originally lower, I said no particular
direction, so the answer is the second, but you probably meant it could
go either way, correct?

I also normally work with YO on yagis, so I really don't pay much
attention to the resonance, just the real portion of the impedance.
Then I fix it when I build the DE and match.
tom
K0TAR