* what cable did you use for connecting the antenna with the tuner? should be a GTO-15 and no coax / copper cable. This is sometimes the problem.
* make sure that this cable is away from other metallic objects and that it is as short as possible, it is already part of the antenna - and the area where most of the power is transmitted
* connection from this cable to the antenna (and tuner) is critical! minimum resistance necessary!
checking/measuring/testing the system (standing wave ratio etc.) needs some specific technical HAM radio knowledge.