But I am now more confused than ever I now know that they are part of the HF antennas but I am totally confused about it so its just the start of a long antenna that is much bigger than which is actually visable on the outside? its the moving bit that confues me, what moves ?
The total length of the antenna has to match the frequency at which you are
transmitting. This enables the most radio energy to be transmitted. For reception, it's not very important (that's why a coathanger stuck in your car antenna socket still allows you to hear your radio).
There are sliding contacts on the wire coil inside the "tuner" or "coupler" as these boxes are usually called. These contacts "tap off" a section of coiled wire corresponding to the correct length required for best transmission.
I suppose there could be something wrong with your tuner. It's the part most likely to fail. By the way, what sort of antenna do you have? Is it strung between the fuselage and the tail?