[TowerTalk] book Tribander comparison test

[jimlux]

On 3/2/11 1:16 PM, Joe Subich, W4TV wrote:
>
>   >  The extra elements give you extra degrees of freedom.  It's like
>   >  building a filter.  More sections gives you the ability to have a
>   >  passband that's wider and flatter.
>
> I haven't seen a successful (95% efficient for the total boom length)
> OWA design that covers 20/15/10 meters much less 20, 17, 15, 12, 10
> and six meters.
>
>

I was actually referring to a single band design.. if you have 4 or 5 
elements for a single band, you can simultaneously get flat Z across a 
wide band, good F/B, and good directivity.

For a multiband design.. I doubt it.  The F12 multiband 20/15/10 is 
basically a 3 element on each band, with a clever design to use a single 
feedpoint, and it's getting pretty cluttered on the boom with 9 or 10 
elements already.

There's probably some elegant mathematical proof (along the lines of 
Chu's and Harrington's) that says you can't get there with the 
constraint of all being on the same boom and interlaced  (e.g. having a 
really long boom with a 20m 5 el Yagi, a 15m 5 el Yagi, and a 10m 5 el 
Yagi, arranged end to end, probably isn't a "good" solution, even if the 
RF performance would be fairly good.