ve2pid wrote:
My question: Should I remove the old balun or may I keep it, i.e. does
it has any influence even if the coax is removed?

It is unclear where you have connected your ladder-
line at the antenna end. Is it connected through the
coax connector or does it bypass the balun and connect
directly to the antenna wire, i.e. are you trying to
use the old balun as your center insulator?
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73, Cecil http://www.w5dxp.com