[TowerTalk] Broken 5-Element Yagi

[Bill Stacy]

Hi, All:

Steve asked the following:


    Suppose you had a typical 5L 20M beam and the  reflector fell off. What 
is the real story as far as gain goes? Is it a drastic  drop or what? Any
other 
implications? I obviously don't do antenna modeling  or I would have an 
answer already. TIA.

--------------------

I ran a quick model using EZNEC.  Here's what I found (assuming the Yagi at
70 feet above ground):

Model		Gain (dBi)	Z

Intact	14.94		22.2-j14.17
Broken	14.35		29.75-j22.1

I attached a PDF of the two patterns.  There is not much difference in
forward gain.  The interesting thing, however, is the degradation of the
F/B.  Without the reflector, the F/B drops drastically.  This mirrors the
experience I had when the reflector on a 4-element came off.  

I think it was Dave Leeson who wrote something to the effect that "Yagis
just want to work."  :-)

73, Bill, N5TU