Topband: vertical balun

[Bob Kupps via Topband]

Hi we have a 30m top loaded monopole with the feed point about 2m above a large ground radial field. Right now we are feeding it through a 4:1 balun (not a unun) with 12.5 ohms on the balanced side, and the SWR is 1.4 with no matching network. Is this balun acting as a common mode choke? Do we even need a choke? Would an unun be better?

Thanks 73 Bob HS0ZIA