You are lucky to see the gain you have, considering the lack
of decoupling...Or at least in that pix....Also, thats a
pretty lame yagi, so like you say, not really a fair test...
My 3 el vertical yagi would eat that j pole for lunch, being
it has about 9.4 dbi gain...Or about 7.3 dbd....
The J poles are ok I suppose, and are good for people with
copper and torches...But they would be even better with some
additional decoupling...I bet they still have trouble matching
the old isopole that was made by AEA...That antenna was well
decoupled. Looked like a ballistic missile, but it was hard
to beat as far as performance. It was generally the benchmark
most other dual 5/8 designs were judged by.
:/ MK