[SCCC] Is F/B Ratio Really Important?

[Tom Rauch]

> 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.

It is also possible to phase two elements on 40m and have 
over 20dB  F/R and 11.5 dBi gain (over real earth) at a 
modest 70 feet of height. That's what we do with a 
multiplier/short distance antenna here, since that tower is 
small.

In comparison my 47 foot boom  3 element 40M at about 85 ft 
has 13 dBi gain (over real earth) and only 23dB F/R.

We paid a big price in cost, weight, and windload to use the 
3 element antennas for about 1-1/2  dB more gain and about 
2dB of improved F/R...but the bigger antennas certainly look 
much more impressive and were available off-shelf. (The 2 
element 40 is homebrewed from what used to be a F12 two 
element linear loaded 80M antenna.)

By the way I almost never find a single 40 at low height 
better than the 40M stack (bottom 85, top 170) at any 
distance, unless it is within 500 miles. I'll know about 20 
and the rest in a few months when the higher frequency 
antennas are finally installed. The 40 is pretty much always 
locked into stack mode unless I want to work really short 
distances.

73 Tom