[TowerTalk] yagi f/b and rx s/n

[Jim Lux]

On 1/13/13 8:18 AM, john at kk9a.com wrote:
> You can easily design a 2el monoband yagi with 50 ohms impedance and
> reasonable gain.  Trying to design one for multiple frequencies using a
> fixed boom length is more of a challenge.  I always focus my designs on gain
> first and then SWR and F/B.  If you really want good F/B you'll have to add
> another element to your beam.

I think the OP has variable length elements, so what's he presumably 
looking for is how to pick the boom length...

>
> To:Tower Talk List <towertalk at contesting.com>
  This will be assembled from
> SteppIR components that I have on hand, so dimensions can be optimized
> for each frequency once a boom length is chosen.


N1EU, you need to decide if you want to optimize for gain, or whether a 
dB is important, because that's really the tradeoff.  All two element 
Yagis will have *about* the same gain, what changes is the depth and 
width of the null to the back.

You can make that back null narrower or wider by changing the element 
spacing.


Have you thought about driving both elements and doing a W8JK type 
antenna? (two elements driven out of phase and closely spaced)  You can 
get a very narrow beam width, at the expense of low electrical 
efficiency so gain is somewhat below the directivity. And you get a beam 
in both directions.  But up high enough, when the sunspots are right, 
maybe that's what you'd really want.. When 10 is hot, it seems like the 
directivity is what you want, to point to the side of a bunch of people 
you don't want to work.