>>I think marketing and folklore has us all convinced stubs are lossless.
>>Just like lumped components, ALL stubs have loss. Coaxial cable stubs can
>>be particularly lossy. They just have so much surface area, they spread the
>>heat around so the temperature rise isn't great.
>
>
>Interestingly, in the W9LT/K3LR-design lazy-vee parasitic array, the losses
>in the floating feedlines of the non-driven dipoles (which are
>open-circuited stubs) actually improve F/B ratio substantially (though at
>some cost in gain). You can see the change dramatically if you model the
>feedlines as transmission lines (which are lossless in NEC-2) and then
>replace them with loads of the appropriate X and R values.
Ahh, but if you model them correctly, you won't be as impressed!!
I was working on my own version of the above antenna for 80M and using
a perfect X value (0 + j50 ohms). Antenna looked totally kick
butt. Then, because I couldn't use a 1/8th wave open stub, I
went for the 3/8ths wave open stub. Using TLA.EXE (by N6BV),
and using RG-8X as the transmission line, the actual impedance is,
are you ready?
5.62 + j49.69
Now modeling the antenna again, with this "real world" impedance
of the stub, it doesn't look so good! It introduces quite a bit
of loss and messed up the F/B as well.
I thought the lazy-v paristic array was the greatest 80M wire
antenna since sliced bread. It's not quite so when you model
it accuratly.
---
Chad Kurszewski, WE9V e-mail: WE9V@qth.com
The Official "Sultans of Shwing" Web Site: http://www.QTH.com/sos
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