Using Unequal Lengths for a Phasing Harness

Alright, maybe not the clearest title for a post, but hey. 🙂

Anyway, in my previous post about what I plan to do with my phasing harness for stacking my planned WA5VJB "Cheap Yagis" I was deliberately attempting to keep things simple so as to keep the post short. However it has been brought to my attention that the over simplification may possibly lead people astray, so let me correct something and provide you with some more information to ponder.

In my previous post I said:

"(But keeping in mind that the lengths have to be the SAME odd multiple – so both 1/4wl or both 3/4wl – otherwise the phase will be out and potentially cancel or something.)"

Now I made mention here two things:
1) The two lengths must be the SAME; and
2) If they're not the SAME they'll cancel each other because they're out of phase.

This was an over simplification so let me make these two elaborations:
1) The two lengths can be DIFFERENT – as long as they're both an odd multiple of 1/4wl; and
2) If they're different that can result in the two beams being 180deg out of phase – for example if 1/4wl was used for one and 3/4wl used for the other.

If you do chose to go with a setup that results with them being 180deg out of phase and you have them both orientated the same way then they will cancel each other out – kind of defeats the purpose hey! But there is a simple solution. You rotate (along the axis of the boom) the beam 180deg. This will then obviously put it back in phase and maximum benefits will be realised.

In fact, VK1OD has done that with his setup detailed here:

With mine though, I plan to keep it as simple as possible (as it's my first attempt) so I'm going to use identical lengths and identical beams. 🙂

But on this note, I will post up another post on the basic theory of how the 1/4wl section (also colloquially known as a "Q-Section") works as an impedance transformer; as well as the formula for working out what Q-Section you need (as in what impedance) and also the significance of a 1/2wl section (explaining thereby why we specifically want odd multiples). And all that is based on phasing, so stay tuned. But that probably wont be today, however hopefully one day soonish. 🙂

Have a good week-end!!

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