On 6/22/2011 7:31 PM, tom wrote:

I've built many 6m beams with no correction added and using simple
homebrew U clamps. I have seen little discernible difference in their
performance from predicted. Of course I shouldn't except perhaps in the
side nulls. And they seemed about right. One small confirmation was the
SWR curve also matched predicted.



Based on a fair number of simulations over the years, I'd say that SWR
curves are not very sensitive to pattern degradation (except in an
egregious case)..

Consider a 5 element medium gain Yagi where the currents are all roughly
equal (which is what you'd have with moderate superdirectivity) and it
has a F/B ratio of, say, 20dB.

Screw up the current in one of the elements by, say, 25% (so the overall
excitation is now off by 5%).. That's enough to turn your -20dB null
into a -10dB null (in round numbers..)

But, would you even see that in a VSWR.. say it was 1.2:1 before
(reflection coefficient = 0.09).. and now the reflection coefficient
changes by 5%.. so it's 0.0945.. That's a VSWR of 1.208.. I think you'd
have a hard time measuring that..