[TowerTalk] Modeling the OH1TV "Opposite Voltage" Feed System for Phased Arrays

[Lux, Jim]

On 1/4/21 7:49 AM, Richard (Rick) Karlquist wrote:
> I never heard of this scheme, but many years ago modeled
> and/or built numerous 2 element driven arrays that
> were similar to this, except that I didn't use a half
> wave transmission line between the elements.  There are
> various configurations that I have successfully used.
> It isn't clear to me that the half wave line is
> necessary or even optimum, although it will certainly
> work.  I also agree with the article that you should
> deal with matching to 50 ohms with a separate network.
> That is what I always did.  IMHO, driven 2 ele arrays are
> the way to go, vs parasitic, because of the superior
> gain, F/B and bandwidth.
>
> Rick N6RK 

I think the 1/2 wave line makes it slightly easier to design, since the 
impedance is the same. And it enforces the voltage constraint. Of course 
that's only true for one frequency.

I assume that Dan's AutoEZ model calculates the mutual impedances, 
although it's not clear from the QRZ article.



Ultimately, too, you probably want the element currents the same (in a 2 
element array), rather than the voltages the same.


I agree that all driven arrays are going to be better, with the tradeoff 
of more complexity. And with modern computer controlled LC networks, 
there's no reason not to make it frequency dependent.
(Unfortunately, LDG doesn't sell their RS-232 controlled tuner any more, 
and none of the usual players seem to indicate that this capability is 
available).

I suspect that you could do a 3 element triangular array and get 4 
square performance with the right tuning approaches.