[TowerTalk] Re: Yagi's

Tom Rauch W8JI@contesting.com
Mon, 5 Feb 2001 18:21:21 -0500


As for your antenna, on ten meters you have you have: 
> Yagi, < 1 WL boom,13 elements 3 of which are reflectors at 65 feet.

My three element 40 meter yagi over the same percentage 
bandwidth with only three elements on a boom shorter than 1/2 wl:

13.8 to 14.4 dBi gain.
F/B better than 20 dB
SWR under 1.35:1

In contrast your antenna has more than twice the boom length and 
over four times the elements, yet only has 2 dB more gain and 5 
dB more F/B at bandwidth edges!

If I consider front-to-null, since the null is placed at a useful angle, 
my common less-than-half-wave boom antenna has more than 45 
dB rear rejection across 3% bandwidth.  

I can't find a 1 wl boom Hygain antenna, but an optimized 24 foot 
105BA over earth has:

16-16.2 dBi gain
23-27 dB F/R

It sure doesn't look like anything remarkable is going on. 

Your antenna works about like any 1 wl yagi should work, even one 
with 5 elements instead of 13 elements.

I'm sure you will want to shoot me for saying this, but it looks like 
much ado about nothing to me. Gain is proportional to boom 
length, and F/B is mostly a matter of element placement and 

Yagi's have been investigated pretty well over the years. They have 
evolved into single reflector yagis with multiple directors because 
that is what gives the best performance for a given size and cost.

People can natter all they want about gain and stuff, but the truth is 
there is very little (if any) difference between the magic antennas 
and any other antenna the same physical size, assuming no one 
did anything wrong in the design.

There is no free lunch.


73, Tom W8JI

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