[SCCC] Is F/B Ratio Really Important?

[W6ph at aol.com]

In a message dated 12/30/2007 4:11:58 PM Eastern Standard Time, 
w8ji at contesting.com writes:

I never look at take-off angle. I look at absolute gain at a 
desired angle or range of angles, which is different than 
looking only at TO angle.

Another thing I try to avoid are multiple nulls in the 
useful area of the pattern.

73 Tom, W8JI 

 
Take-off angle depends on the height of the antenna, not the gain.  This is 
the reason that people stack antennas, to fill in the takeoff angle nulls that 
occur as a result of height.  This is very popular in the northeast where 
Europe is relatively close and low antennas work well when the band has opened.  
The high antennas open the bands and close them.  Another issue to think about 
when designing yagis is the beam width.  If you want to cover a 60 degree beam 
width, then a 4 element beam may be optimal for you.  A lot of the northeast 
contesters purposely use the lower gain antennas for greater beam width and 
take advantage of the different heights of the stacked antennas to fill in the 
"box".  N6BV has written a lot about this.
 
On the west coast, the needed beam widths are relatively narrow and the 
distance to cover is very long.  Hence, high gain antennas at good heights are 
better.  That is why I am way down in the pileups with my A3S at 45 feet in Lone 
Pine.
 
The optimum gain of a 2 element yagi is in the order of 6 dbi but has a very 
low front to rear ratio.  By going to a 3 element yagi, the gain goes up to a 
little over 7 dbi and F/R's in the order of 25 db are achievable.  But the 
boom is twice as long.  This begs the question, "Is a 3 element 40 meter beam 
really worth the extra effort over a 2 element yagi?"   Probably not if F/R is 
not a consideration.  W6SAI was a strong proponent of the 2 element yagi for 
these reasons and wrote about it numerous times.  I like the Cushcraft 40-2CD.  
 
                                                              73, Kurt, W6PH 



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