Topband: Topband loading coil

[Max Cotton]

I have an inverted L antenna resonant on 80m, I decided to add a loading coil to the base to bring it on frequency for TopBand. I wound a 2.5mm wire coil 16 turns on a bit of square Paxoline board by drilling holes into the board each side and feeding the coil through the holes, a bit of a struggle but it worked, not very pretty, it is 146mm diameter and 120mm long 30.5uH. When I first tried it the SWR after small trimming was 1.2:1 band centre and 2.0:1 band edges. Now it looked a but ugly, so I decided to neat it up a bit by adding two fibreglass webs so the coil was now  circular and held by a cross section instead of just the one plane,  now when I retried the SWR it is still resonant on 1.800 but the SWR is now 2.0:1 in the middle of the band and 4.0:1 at the edges  the turns are the same, the inductance is the same but I have lost my fine SWR curve. I only added the fibreglass and neated up the coil, Ideas what to do next apart from removing the fibreglass webs and going back to ugly coil?73 Max M0GHQ