I've seen plans for coax collinear designs where the top 1/4 wave
element is shorted back down onto the below element, and I've also
seen plans where the 1/4 wave top element just comes straight up and
they didn't put a jumper across to the other element to short it. I'm
wondering, has anyone experimented with both methods and noticed any
significant difference? Is there a best way? Also, does the shorted
method make it DC grounded?

Thanks for any info,