Roger,
Each HI-Z amp (impedance buffer) at each element already has a 1:1 “braid
breaker” choke at the input so is already isolated from the feedline.
The chokes at the combiner prevent all the feedlines together them from acting
like a ground screen. Without the chokes, they are all RF bonded together.
John W1FV explained this in his original NCC paper how it upsets the pattern.
I have thought about redesigning the combiner board with integrated 1:1 toroid
braid-breakers on each feedline (just like the element amps) but haven't got
around to that.
That would be a lot cheaper and easier than installing out-board chokes.
Steve, ve6wz
> On Sep 23, 2021, at 12:50 PM, Roger Parsons via TowerTalk
> <towertalk@contesting.com> wrote:
>
> I have recently completed building a YCCC 9 Circle array, and it seems to
> work quite nicely. This replaces a receive 4 square using top loaded elements
> - I could never get that to last as animals would break one or more of the
> top loading wires mistuning the array.
>
> The instructions for the YCCC array are explicit that there must be common
> mode chokes between each element and the combiner unit. That is obviously a
> good idea, but I can't understand why they suggest putting them at the
> combiner unit end of the feed lines to each element, and my feeling is that
> they should be at the element ends. (The elements have a very poor ground,
> and the feed lines are significantly long. Surely that means that the high
> impedance of a common mode choke at the combiner will be transformed to a
> different and probably lower impedance at the element. The effect of that
> could be that the feed line becomes the main and unpredictable ground for the
> element, and different for each element, which I think is exactly what is not
> required.)
>
> Comments would be appreciated.
>
> 73 Roger
> VE3ZI
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|